Please - how do you clear the sludge, of mixed antifreeze types, out of the radiator and heater matrix ?

[Bfg]

Please - how do you clear the sludge, of mixed antifreeze types, out of the radiator and heater matrix ? 

I've just recently bought an old jag,  .. but this topic is pertinent to most classic cars ...   

During general maintenance,  I'd noted the antifreeze was a very light pink colour (HOAT) whereas on this age of car it should be blue (IAT).  However it was clear of brown sludge.  And so this weekend, I drained the pink out (removing the bottom hose) and flushed the radiator out with the garden hose.  In doing so.,  I noted unusual (to me) mix of coloured bits in the catch tray .. pink, blue and dark coloured particles (the latter of which were probably rust from the old cast-iron block).  I took a photo . . .
 

When refilling the radiator (with 50:50 blue antifreeze) I noted that it was annoyingly slow filling. I've also have issues with the heater not working, and so I bled that by removing its top hose. I noted the heater matrix (as I pumped water through) was already full of coolant, with a blue tinge to it. But even after bleeding and restarting the engine - hot water doesn't flow through it (its pipes remain cold).  

I been led to understand the issue to be ; the car's original antifreeze was blue IAT, and sometime before I got the car its been refilled or topped up with pink HOAT, which is not compatible.  ..suggesting that the mix of these two chemicals creates a sludge.   Adding 1 + 1 to equal 3  I'm having to presume this is the cause of the coloured particles in the catch tray, and more importantly the very slow refilling of the radiator core ..and the lack of flow through the heater matrix.   Alternatively of course someone might have tried to seal a radiator leak with a chemical solution. 

There was also pink crystalline particles around the thermostat gasket. . .

I've also noted the thermostat's gasket face is corroded away. . .Being the new owner-mechanic I don't know whether that corrosion is related, but the gasket face now needs redressing smooth and flat.  

And again, although possibly unrelated.. the water pump bearings are on their way out.  A NOS pump is on its way. 

Furthermore, I don't know if the situation has been aggravated by the wrong thermostat being fitted (it should have been of the sleeved type, to close off the bypass hose).  As a consequence there's been lesser flow was through the radiator itself (..the bottom of the radiator was cold, when the top and the thermostat were at 83 degrees).  I've now sorted the by-pass issue / lack of thermostat sleeve.. by fitting a restrictor disc in the bypass hose. I'm told this is not unusual practice.  

The car had only driven (..according to MoT records) just 310 miles over the past ten years.  I have been recommissioning her since mid January, and last month drove 380 miles. Normally, the temperature stays at 83 degrees (when the thermostat opens) but soon rose to 95 degrees when stopped slow crawling n traffic for ten minutes.     

So to reiterate - Please - how do you clear the sludge, of mixed antifreeze types, out of the radiator and heater matrix ?    I can flush again, I can back-flush, and even remove the radiator to shake it all about, but is there a chemical cleaner that will help dissolve the sludge blockages  ?  

One contributor to another forum suggests Fernox F8, domestic central heating cleaner .. "a super strength, fast-acting cleaner for heavily contaminated, dirty and problem central heating systems. Its citrate-based, pH neutral formulation removes debris, sludge and scale without the need to neutralise. "   

As my car's radiator is a brass one, with soldered joints, and the engine's cylinder head and catch tank are both aluminium, I'm naturally keen not to dissolve these parts and end up with more of a problem than I already have. 

Your experience / advice would be much appreciated - Thank you 

Pete 

[Chris Hale]

Lemon juice is supposed to work well removing sludge,  it that I have ever actually had to try it.

Heater radiators normally clear if you back flush them with your garden hose or if you have a compressor you could use that on a low setting 

[trchris]

Hi Pete that looks certainly like the wrong antifreeze was used in the past, possibly because it’s cheaper as l have mentioned in your other post the magic chemicals sold by motor factors are cash gathers for the manufacturer and don’t work, some maybe if used from day one and yearly. Could you  remove the radiator lay flat and use the Fernox solely on it ? Also taking both heater hoses and flush the matrix without getting any Fernox into the engine waterways ? the only problem you have is water is the same as electricity it’ll take the path of least resistance so will bypass the blockage . You may have to bite the bullet in the end and have the rad professionally flushed/ recored.

Chris

[stillp]

I believe the Rolls Royce Owners club contacted Fernox and was told that the Fernox cleaner is perfectly compatible with the mix of metals found in older cars.

Pete

[Trev Good]

I have used fernox to great success on the 3, not so on the 6!

[john.r.davies]

HOT water?  Reversed if necessary.

"Lemon juice" is citric acid, which is available in more quantity and convenience than a barrel of lemons.  I'm guessing that any 'weak' organic acid, eg acetic, oxalic, ascorbic, tjat may alsi be nought in quantity, would do as well.

John

Edited April 5 by john.r.davies

[Bfg]

Thanks all for your thoughts and suggestions. 

 

1 hour ago, john.r.davies said:

HOT water? 

You mean hotter than the engine's water-coolant mix at over 100 degrees ?  

 

1 hour ago, Trev Good said:

I have used fernox to great success on the 3, not so on the 6!

Thanks Trev, good to hear from someone who has personally tried the Fernox in a car system and had success. 

The instructions on the pot, for domestic central heating, recommends circulating it for up to a week, before draining down and flushing the system thoroughly.  Do you recall how exactly you used it ? 

2 hours ago, stillp said:

I believe the Rolls Royce Owners club contacted Fernox and was told that the Fernox cleaner is perfectly compatible with the mix of metals found in older cars.

Pete

Hope that's so.  If so it's good news. 

The company website say it's environmentally safe to drain away down drains. 

Pete

 

 

Edited April 5 by Bfg

[harlequin]

Pete

Time for a science experiment

Take some of your sludge and put it in a series of bowls then add the various suggestions to a bowl each, 1 with lemon juice, 1 with  fernox, 1 with white vinegar and so on

George 

[john.r.davies]

"You mean hotter than the engine's water-coolant mix at over 100 degrees"

No!   Water supply to a garage is usually cold.  You need special persuasive skills to attach a hose to a kitchen or other  hot water tap!

[Trev Good]

Hi Pete, 

I just had the fernox in the system for four long drives over a couple of weeks and that seemed to clear everything.

[Charlie D]

Pete,

When I rebuilt my 3a I put OAT antifreeze in it without a thought.

After a thousand miles or so I lost all oil pressure. It turned out that the figure of 8 seals at the bottom of the liners had corroded, even though they were brand new 1000 miles before. (I forget if they were steel or copper), the antifreeze had leaked out and got into the oil. The oil had turned into a white goo that had the consistency of very soft chewing gum.
It even made removing the oil filter can a chore.

The actual water/antifreeze did not seem to be affected.

Having only just rebuilt the engine I didn’t want to pull it all apart again, so I cleaned out what I could of the goo, without removing too much of the engine (Yes, I should have taken it all apart and started again, but I didn’t have the inclination, but I did have to replace the Fo8 seals ) I flushed it with paraffin/petrol/diesel (I forget exactly what) then refilled with oil and Fernox.

After 500 miles I replaced the oil again

I’ve now done over 5000 miles and it doesn’t seem to have caused any permanent harm.

I do realise that it’s not the same situation as you Pete, but it shows that it’s best to stay away from OAT antifreeze.

The other BIG advantage of Fernox is that it is safe for pets to drink .

Charlie.

[Steve-B]

On 4/5/2026 at 7:12 PM, john.r.davies said:

"You mean hotter than the engine's water-coolant mix at over 100 degrees"

No!   Water supply to a garage is usually cold.  You need special persuasive skills to attach a hose to a kitchen or other  hot water tap!

In our current house and the previous house when we had a Megaflow tank installed I had the plumber install a standard tap on a small branch from the tank (that feeds the house). That saved an engine on our ex-Caterham when I put the wrong coolant in combined with Fernox to flush it. YMMV.. 😉 

[Bfg]

Thanks Trev, Thanks Charlie.  I had Fernox on order from B&Q and after 36 hours it was delivered this morning.  In readiness for that ; yesterday I flushed the car's system back n' forth with mains water.  Very little, in way of bits, muddiness, or grime, came out . . .

        

^ After draining down the blue antifreeze, which I had used last week, I twisted the radiator's bottom hose around and connected the garden hose pipe to it, using the hose pipe's clamp to gently clamp it in place.  The radiators top hose I temporarily replaced with an old bottom hose I'd taken off Katie's (my TR4A) engine (which I'd replaced with stainless steel between the rubber hoses).  The end of Katie's hose I simply extended with a length of vacuum cleaner pipe ..so water would be directed into the catch tray.  Btw., the distributor, which is situated under the top hose, was cover with plastic bags to avoid too much moisture pouring over its electrics. 

^ Back flushing (garden hose in the bottom on full pressure) I thought might have lifted some of any contaminates out of the radiator, but in fact very little came out.  

    

^ Having drained the radiator, by removing the engine's bottom coolant hose, I hadn't expected much to be inside the engine itself.  But back flushing into the thermostat housing (with thermostat itself removed) issued a pool of clear blue antifreeze in the catch tray,  But for just a few very small blobs of purple gel, it was again free of debris and contaminates. 

This however was a lesson for me .. because I hadn't back-flushed the block last week, when I switched from the pink (HOAT) antifreeze to the blue (IAT). . . I might assume the prior-owner or mechanic likewise hadn't when he drained down the radiator and refilled it with the pink antifreeze.  The blue antifreeze within the engine's water jacket hadn't been flushed out - which in turn led to the chemical reaction (gelling) between the two different types of antifreeze.   

    

^ Next up I wanted to check the car's heater matrix, as it's likely that it too hadn't been individually flushed out.  I was right.  I'd disconnected the heater's hose connections and replaced the feed pipe with the length of petrol tank breather pipe I'd not long ago replaced.  Again, the piece of vacuum cleaner drain-pipe directed the flush down passed the exhaust manifolds and chassis into the catch tray.  Aside from just a few larger gelatine blobs, back-flushing the heater-matrix issued this green-yellow coloured coolant of gel slime particles. There was nothing hard nor very big but I've never been a fan of pea soup, and who knows what it might congeal into . . .  

Neither pipe to the heater matrix would flush. 

      

 ^ I pulled the heater valve and it was blocked.  Now I know the answer to  "I've never been a fan of pea soup, and who knows what it might congeal into ".    

   

^ I first tried cleaning the pipe out with a screwdriver. The crud in there was hard and dry.  I know.. it's hard to believe that the car's heater didn't work !   The rivet seen at the top of this photo was drilled out, and then the two halves of the body twisted, to open the valve up.  Only then could I clean out its insides.  The valve's rubber diaphragm will need replacing as it's all shrivelled, but for the time being it appears to work and so the crystalline deposit was carefully cleaned off but otherwise it was left untouched.

    

^ It took a good while but the valve cleaned up fine (aside from the aforementioned shrivelled diaphragm), but the copper pipe was also solidly blocked. Full garden hose pressure didn't shift it, but the screwdriver did.     

The other pipe, from the water pump, to the heater matrix also appeared to be blocked, but once I disconnected the bottom connection of that pipe from the pump it flushed through easily.  Even so, when reconnected, I still couldn't back flush though the water pump.  I don't know if that's usual or whether there's a blockage there.  As the pump will be changed next week, I left it alone and reassembled the cooling system's plumbing and refilled it with fresh tap water.   

I've swapped the 82 degree thermostat for a 74 degree one (Thanks Rich C-R) , and yesterday evening just drove around the block.  The heater's still not working ..which is a nuisance because I would have liked it to be through-flowing for the Fernox to work within its matrix.   I'll try and get the water pump's heater connector off now, and then again refill, but this time with the central heater cleaner in the system. 

Work in progress.

Pete

 

 

[Z320]

I never had any issues like this at all with Gysantin G48 (German badge from BASF).

My test would be how the sludge is possible to dissolve with #1 petrol, #2 hot water, #3 technical alcohol

To flash the engine with technical alcohol could be an interesting issue with a conclusion to other disease.

Edited April 10 by Z320

[Charlie D]

Pete,

Just realised that you were talking about Fernox F8 CLEANER.

I my case I meant that I was using Fernox ALPHI-11 ANTIFREEZE.

This again was recommended by RR (I believe).

Do you intend to finally fill using Blue antifreeze?

I wonder if that will react with the Fernox F8 cleaner that will be left in parts of your engine maybe.

Using Fernox ALPHI-11 antifreeze would, obviously, be no problem. Plus it lasts many years more before it needs changing as opposed to the blue antifreeze.

The main reason I used it was because we have cats.

Charlie.

Edited April 10 by Charlie D

[Bfg]

 

On 4/10/2026 at 12:16 PM, Bfg said:

The heater's still not working ..which is a nuisance because I would have liked it to be through-flowing for the Fernox to work within its matrix.   I'll try and get the water pump's heater connector off now, and then again refill, but this time with the central heater cleaner in the system. 

     

^ I removed the hose connection, of the heater pipe, on the water pump ..and although the rubber tube was clear - the spigot into the water pump was blocked hard with crystalline whatever.  Using a flat bladed screwdriver I got a lot of it out and although I could see wet in the bottom, no coolant was flowing out, despite the head of water of a filled radiator, filled top hose , etc.    I was going to undo the connector into the side of the water pump, but when I discovered the bolt's head sizes were different I thought better than to tamper with it. 

     

^ However poking around with a piece of stiff wire broke through the incrustation and coolant flowed out freely.  I poked around as it was doing so to dislodge Klingons, before refitting the rubber hose to the heater.   Odd thing is that the coolant came out blue, despite my having flushed, and back-flushed the radiator and the block, and heater, and its pipes ..after which I've only refilled with tap water.  So, where was the blue antifreeze hiding ?   

In topping up again ; I now added Fernox F8 to the water.  The manufacturer's instructions says the half-litre contents of this bottle is good for a central heating system of 130 ltrs.  My car's coolant system is 13.5 litres so logically 1/10th of the contents should do the job. Instead I measured 2/5th (200ml) into the car's water.

    

^ I also added a squirt of the stuff to the small catch trays with the bits in it. The blue bits are from the heater valve, the pink bits are from the radiator flush.  I've stirred the Fernox in (it has an orange tint to it like strong pee) and have gently heated each on the cooker ..to simulate a central heating system or the car's cooling system. I'll now monitor those over the next couple of days to see if I can see any breakdown of those bits.  

I've just driven an 18 mile, round trip, to the boat and the car's heater now works    I stopped for a leisurely coffee ..to allow the car's water-fernox coolant to settle again.  And then I stopped for groceries on the way back ..to sit in four o'clock Friday afternoon commercial / industrial estate traffic. 

With the 74 degree thermostat fitted, no anti-freeze only the Fernox cleaner ; the coolant's temperature gauge now reads closer to 72 degrees.  The heater's warmth is notable when the heater's fan is on, but is only a gentle waft of warm air when the fan is off, but its vents open. This is as per the operator's handbook.  which I can happily live with in a closed car. 

I'm glad to finally be trying the Fernox cleaner ..circulating through the whole system including the car's heater. 

I'm meeting a friend tomorrow, with a Triumph GT6, with the intent on going up to Rickenhall (IP22 1HD) Classic car meet, autojumble and rummage. If anyone would like to join us.  That'll be another 2 hours of cross-country driving /  75 mile round trip for Carmen.  I'm a little concerned that the water pump is rattling more & more... I might only hope we'll make it without breakdown.  

I'll let you know how I get on with the temperature and the cleaning in a few days time.  

Pete

  

 

Edited April 20 by Bfg

[Bfg]

4 hours ago, Z320 said:

I never had any issues like this at all with Gysantin G48 (German badge from BASF).

My test would be how the sludge is possible to dissolve with #1 petrol, #2 hot water, #3 technical alcohol

To flash the engine with technical alcohol could be an interesting issue with a conclusion to other disease.

Marco,

I've been led to understand the issue here is not so much with the anti-freeze, but the mixing of two incompatible types.  

Whether the pink antifreeze (HOAT chemical composition) is bad for these old cars - I honestly don't know.  What I do know is ; the blue (IAT) antifreeze is what has always been recommended .. and so that's what I want to use. 

I've often found ; if there's a potentially incompatible issue with something new .. putting it back to standard often helps working things out.

Pete 

 

[trchris]

Hi Pete 

It’s obvious that you’ve found the problem with the cooling system , the mixing of both types of antifreeze and the infrequent use over a long period of years has caused your headache so to speak. It’s yet another example of poor knowledge from a previous owner/ supposedly mechanic , who should know better you’d have thought but at least you’re now on top of it . You’ll soon have her purring like she should 

Chris

[Bfg]

 

3 hours ago, trchris said:

Hi Pete 

It’s obvious that you’ve found the problem with the cooling system , the mixing of both types of antifreeze and the infrequent use over a long period of years has caused your headache so to speak. It’s yet another example of poor knowledge from a previous owner/ supposedly mechanic , who should know better you’d have thought but at least you’re now on top of it . You’ll soon have her purring like she should 

Chris

Long way to go yet Chris, but one step at a time I hope to get there.  "Purring like she should"  sounds good.  

[Bfg]

Update . . .

 

On 4/10/2026 at 5:15 PM, Bfg said:

n topping up again ; I now added Fernox F8 to the water.  The manufacturer's instructions says the half-litre contents of this bottle is good for a central heating system of 130 ltrs.  My car's coolant system is 13.5 litres so logically 1/10th of the contents should do the job. Instead I measured 2/5th (200ml) into the car's water.

    

^ I also added a squirt of the stuff to the small catch trays with the bits in it. The blue bits are from the heater valve, the pink bits are from the radiator flush.  I've stirred the Fernox in (it has an orange tint to it like strong pee) and have gently heated each on the cooker ..to simulate a central heating system or the car's cooling system. I'll now monitor those over the next couple of days to see if I can see any breakdown of those bits.  

 

After flushing and back flushing both the radiator and engine block, and then also the heater circuit separately (removing specific pipes) - I'd refilled the car's 13 ltr cooling system with 200ml of Fernox F8, to help clean it out..  As recorded, I also added a squirt of the stuff to my stainless steel catch trays with the bits of the antifreeze contaminates in it. Additionally I added a spatter of fresh solder to each tray, because I reasoned that's probably the softest metal in the cooling system ..and if that showed visual or tactile signs of deterioration then I'd be wise to quickly flush the Fernox out.    After seven days of occasional heating and light agitation of the water in the trays - this is what I have. . . 

    

^ Before and After 7 days in the Fernox-water mix.   It's really difficult to take comparable photographs without exactly the same lighting through the kitchen window, but still ; I hope you can see that in each tray (the pink antifreeze contaminates in the foremost tray, and the blue antifreeze contaminates in the tray behind) is colouring what was perfectly clear water. The bits in each appear to be less gritty, but really the process is happening very slowly indeed.   

Good news is that I cannot see, nor feel, any deterioration of (even any less sheen from) the thin splatters of solder that I'd added to the mix.  Accordingly I'm feeling confident that the radiator and heater cores are not being damaged.  

^ I've just taken a sample from the header tank of the car's cooling system (into yet another stainless steel dish) and you can see that despite repeatedly flushing a week ago, and having driven 160 miles since, according to the odometer - the water has lightly coloured to the blue antifreeze.  

I'm a little surprised that it's not in the slightest rust tinted, but on the other hand I'm happy that its so clear and clean.  According to the box of invoices that came with the car, this engine may have been rebuilt as recently as 300 miles ago, so perhaps the block's coolant jacket was chemically cleaned out at that time - who knows ? 

I think tomorrow I'd drain the system down again and replace the water pump, which has a lot of slack in its bearings. This will of course necessitate my removing the radiator ..which I'll then invert and flush again. 

I also want to see if I can adapt a different cooling fan . . .

        

^ I've just bought this Holset of Huddersfield cooling fan ..from a Jaguar XJ6 - Series 1, off of ebay for £30 incl p&p, in the hope that with it being off a 1960's Jaguar ..its bolt pattern might fit.   It's a 12-blade steel 17" dia fan whereas the original (the fan presently fitted) is a 12-blade steel 16" dia.  But I do have a pair of tin snips.! 

The existing XK150 cooling fan works very well indeed, regarding moving air at tickover speeds, but its blades are flat, whereas these have been pressed radially (along their length) to add aerofoil camber to their profile.  The camber stiffens the blades considerably, and then the root of each blade is supported by the doubler-plate (which the original XK fan doesn't have). The much improved stiffness will lessen blade flutter (very inefficient vibration) as well as well stabilising their tip clearance ..away from the fan's cowling.     

At the moment I don't know if the viscous coupling will fit onto the XK150 crankshaft, but this fan's bearings seem to be smooth running and so naturally I'm hoping it will.  I had a viscous fan on my Daimler 250 and, previous to that, on the '66 Jaguar S-type - both worked well as cooling fans, and each was quiet through the range of normal engine revs.

, . .

From what I've read there are various sorts of fan couplings..  each with the objective of allowing the fan to freewheel when the engine is cold &/or as the car passes through the air ..whereby the airflow through the radiator is already there.  Some couplings are mechanical friction between surfaces, while others use a viscous fluid between surfaces or galleries to achieve the same.  A later development of this was, and still is, to use a thermocouple (sensitive to radiator and ambient air temperatures) to control the flow of that viscous fluid, to give more fan cooling when the engine is hot and very little during cold start and warming.  Later still of course the thermocouple switches an electric fan ..and no friction of viscous fan coupling is used.  

Pertinent to each type of fan coupling ; According to Holset's US patent application " the torque required to drive a fan increases as a square function of the input rpm."  

Relationship between Torque and RPM ;   The (engine's) torque required to drive a cooling fan isn't a linear function of RPM, but rather it increases as a square function of the RPM. which in layman's terms means ; if the RPM of the engine & fan doubles, the torque required to drive it increases by a factor of four.

Why the torque needed increases with RPM :

    1.  Airflow Resistance ; As fan speed increases, the resistance to airflow (..the air friction) also rises significantly, and so more torque is required to maintain the higher fan speed.

        For what it's worth .. A quick and dirty calculation < here > suggests a 17" (431.8mm) fan spinning at 3000 rpm has a tip speed of 152mph. 

    2.  Static pressure describes the volume and speed of the air being moved (felt as the pressure of the wind force).  And Static Pressure increases with the square of the RPM change.  ie., as revs increase, the harder the fan must push, or pull, to move that wind force.  And pushing or pulling harder necessitates more torque.*

But, as the car passes through the air ..whereby the airflow through the radiator is already sufficient, the cooling fan is barely, if at all, needed.  So, the various sorts of fan coupling are there to allow slippage between the crankshaft and the fan's rpm ..set to slip when the torque required gets to a certain amount.  Doing so ; saves fuel and lessens fan noise, and possibly vibration too. 

* NB. Static pressure against the fan is cancelled out as the car passes through the air at 70mph ( ..as long as the vehicle has a decent size radiator grille and engine bay through-flow) so additional torque needed to push against the static pressure is negligible.  But high fan speeds still need to overcome the air friction ..especially so where the fan is crude and its blades are fixed / angled to be most efficient at low revs and city traffic speeds.  

The reason I'm exploring this - is to lessen fan noise,  As wind noise through door and window seals is noticeable above 50mph ..I might only assume that, although difficult to define while driving along, fan noise is undoubtedly there.   Anyway..  it's fun to play around. 

Pete

NB. from inside the engine bay you'll not be able to see the viscous coupling, as it's between the fan and radiator, so things will look close to standard.  Whereas an electric fan would not. 

 

 

[BlueTR3A-5EKT]

Is that viscous coupling a good one? 

Cheap enough to replace though

https://www.ashwoodjagparts.co.uk/product-page/viscous-fan-coupling-torquatrol-unit-jaguar-xjs-3-6-6-0-nbc2215aa

[Bfg]

1 hour ago, BlueTR3A-5EKT said:

Is that viscous coupling a good one? 

How do you tell without fitting and trying it. ? 

If it were one of the thermocouple type then it should spin more freely when cold, and as I heat it up - I'd see if the couple between input and fan appeared tighter.  But, as far as I can tell, this one is the earlier type which has resistance in the coupling, of the viscous fluid, which remains (mostly) temperature stable / resistance unaltered until the torque overcomes the air friction at high rpm's ..beyond which it starts to slip.   

I have also looked for signs of fluid leak, there is no indication that the coupling is now empty of fluid or otherwise has air bubbles within.

Perhaps the fluid within may also be somewhat non-Newtonian (aka Oobleck ..according to Dr.Seuss) whereby its resistance is greater at a faster (than hand turning) coupling speed.

I have heated this one, by wafting over its coupling with a blowtorch, and the viscosity / resistance within that coupling is then slightly less (as felt by hand), but I think that is to be expected and likely to be acceptable.  Although I've no prior experienced to judge - I'd anticipate that, even when hot, this coupling has resistance enough to not free-spin at lower engine speeds, when maximum cooling is required. 

Without a proper test rig it's not easy to set things up .. to heat the coupling and at the same time to drive the fan up to the equivalent of 30 or 40 mph. 

I've seen on the internet that you can test it by fitting the fan onto the vehicle, heating the cooling system and then shoving a rolled up newspaper or magazine into the blades to see if the fan stops.  That sounds like a rather dangerous idea to me.   So my only option is to fit it, try it,  and watch the temperature gauge after a run and is then sitting at idle ..to see if the gauge reflects the fan not pulling air through the radiator.    Do you agree ? 

 

 

 

Edited April 21 by Bfg

[stuart]

If thats from a Series 1 XJ6 than they werent that reliable but often the default failure was for the viscous coupling to seize or they would just break off with subsequent rad damage.

Stuart.

[Bfg]

Thanks Stuart, that's worrying.   I'd not heard of such issues befalling the Series 1.  Surely though that must have been a very tiny percentage ..and those which were prone to fail would have done so long before now ? 

[BlueTR3A-5EKT]

Agree with Stuart.  A common failure is seized,  I’ve never seen one sheer though.   TR7 Spitfire and other later Triumphs had viscous coupled cooling fans,.  The other common failure of the coupling was spinning free, identified by the fan not speeding up when the engine is revved. (Your newspaper test)