TR4a Commissioning Thread

[Steven Whitaker]

Insteade of multiple threads I thought I’d just have the one to share my trials and tribulations..

So, when I static tested the over drive switches on the gearbox the one closest to the gear stick is open circuit and closed only in second gear.

The other switch closest to the engine is open circuit all the time so I’m guessing it’s goosed?  When should this be closed circuit?

Also, the hose on the outlet from the water pump blew off yesterday when it got up to temp.  We had steam!  I added hylomar yesterday and today I tried again.  It blew off again.  The top and bottom radiator hoses were cold.  I don’t think the thermostat had opened.  It was tight with a flat type jubilee clip.  It was up to temp pretty much I’d say, with steam showing when the hose blew.  Is it worth trying a wire hose clip, or is there something else wrong?

Thanks.

 

 

[Lebro]

56 minutes ago, Steven Whitaker said:

 

So, when I static tested the over drive switches on the gearbox the one closest to the gear stick is open circuit and closed only in second gear.

This is correct

The other switch closest to the engine is open circuit all the time so I’m guessing it’s goosed?  When should this be closed circuit?

Should be close in 3rd, and 4th, not in neutral. it may need to be screwed further in (or out ?)

Also, the hose on the outlet from the water pump blew off yesterday when it got up to temp.  We had steam!  I added hylomar yesterday and today I tried again.  It blew off again.  The top and bottom radiator hoses were cold.  I don’t think the thermostat had opened.  It was tight with a flat type jubilee clip.  It was up to temp pretty much I’d say, with steam showing when the hose blew.  Is it worth trying a wire hose clip, or is there something else wrong?

If the thermostat is not opening, then there will be much pressure in the system, also adding Hylomar could be acting as a lubricant to assist the hose to be pressured off. Suggest clean everything with solvent (thinners, or brake cleaner etc) then push the hose on & tighten the clip as much as you dare !

Bob

Edited April 27, 2025 by Lebro

[Steven Whitaker]

21 hours ago, Lebro said:

So, when I static tested the over drive switches on the gearbox the one closest to the gear stick is open circuit and closed only in second gear.

This is correct  OK, thanks.

The other switch closest to the engine is open circuit all the time so I’m guessing it’s goosed?  When should this be closed circuit?

Should be close in 3rd, and 4th, not in neutral. it may need to be screwed further in (or out ?)  OK.  How does it actually work?  It's never been out.

Also, the hose on the outlet from the water pump blew off yesterday when it got up to temp.  We had steam!  I added hylomar yesterday and today I tried again.  It blew off again.  The top and bottom radiator hoses were cold.  I don’t think the thermostat had opened.  It was tight with a flat type jubilee clip.  It was up to temp pretty much I’d say, with steam showing when the hose blew.  Is it worth trying a wire hose clip, or is there something else wrong?

If the thermostat is not opening, then there will be much pressure in the system, also adding Hylomar could be acting as a lubricant to assist the hose to be pressured off. Suggest clean everything with solvent (thinners, or brake cleaner etc) then push the hose on & tighten the clip as much as you dare !  OK.  I'll remove the stat and see if its stuck, then clean everything and try again.

Bob  Cheers.

 

[Steven Whitaker]

So, another few hours in the garage tonight.  I took the thermostat out and tested it and it opens fine at 82 deg C ish.  I removed the hose which keeps coming off, cleaned the bre and cleaned the water pump spigot.  I scraped it clean to remove bit of paint and then roughed it up with a file and the. Rough glass paper.  On the spigot, there isn’t any kind of ‘barb’ on the end and I also found a flat on it where the hose connects, so I filed and blended that in to the diameter as best I could.

I opened the heater valve and topped the radiator up with water.  Put everything back together and rand it for a minute without the rad cap on.  I fitted the radiator cap and rand it until normal operating temp.   The thermostat hadn’t opened and I noticed a leak had sprung at the spigot where the hose connects, again.  I could see the hose was slowly working its way off the spigot so I stopped the engine and went for a walk.

Any ideas on the next step please folks?

[BlueTR3A-5EKT]

New bypass hose required?    Pt no 105598.  Plus a couple of new clips.
It truth I have never had an issue with the bypass hose blowing loose or leaking in 50 + years  of TR ownership.

Q.   what pressure does the radiator cap release at?   Should be max 7 psi.   

 

[Steven Whitaker]

1 hour ago, BlueTR3A-5EKT said:

New bypass hose required?    Pt no 105598.  Plus a couple of new clips.
It truth I have never had an issue with the bypass hose blowing loose or leaking in 50 + years  of TR ownership.

Q.   what pressure does the radiator cap release at?   Should be max 7 psi.   

 

It’s brand new!  New clips all round.  Rad cap says 13lbs.

[Steve Priest]

I've found that these Mikalor hose clamps, with an inner steel ring, are good for stopping leaks, especially with silicon hoses.

https://www.ebay.co.uk/itm/304780577386?var=603800778058

Steve

[Ralph Whitaker]

11 hours ago, Steven Whitaker said:

It’s brand new!  New clips all round.  Rad cap says 13lbs.

There`s part of you problem then. Should be no more than 7lb, and the TR4 engine in my 3A runs fine with a 4lb cap and uses no water.

Ralph

Edited May 3, 2025 by Ralph Whitaker

[Steven Whitaker]

23 minutes ago, Ralph Whitaker said:

There`s part of you problem then. Should be no more than 7lb, and the TR4 engine in my 3A runs fine with a 4lb cap and uses no water.

Ralph

Thanks.  But if the thermostat hadn’t opened would the radiator cap pressure still come into play and help?   I’ve got my hands on a 7lb cap now.

 

[RobH]

6 minutes ago, Steven Whitaker said:

But if the thermostat hadn’t opened would the radiator cap pressure still come into play and help?

Of course it would. The rad and engine are linked by the bottom hose too so the system pressure is equal irrespective of the thermostat. 

 

Edited May 3, 2025 by RobH

[BlueTR3A-5EKT]

16 hours ago, Steven Whitaker said:

It’s brand new!  New clips all round.  Rad cap says 13lbs.

Is it rubber or ‘silicon’  ?    Is your new bypass hose a good tight push fit on both water spigots before you fit clips?   

 The only time I have had leaking issues with radiator hoses was a ‘silicon’ item top hose.   I ended up fitting double clips to get it to seal as it was too large internal diameter.    Solution was the the EPDM mesh reinforced with fabric covering top hoses I commissioned with an OE hose maker a few years ago..   Sold by British Motor Heritage as  GRH 453.  
 

[Steven Whitaker]

8 hours ago, RobH said:

Of course it would. The rad and engine are linked by the bottom hose too so the system pressure is equal irrespective of the thermostat. 

 

Ok.  Is it normal for the radiator cap to lift before the thermostat has opened?

[Steven Whitaker]

3 hours ago, BlueTR3A-5EKT said:

Is it rubber or ‘silicon’  ?    Is your new bypass hose a good tight push fit on both water spigots before you fit clips?   

 The only time I have had leaking issues with radiator hoses was a ‘silicon’ item top hose.   I ended up fitting double clips to get it to seal as it was too large internal diameter.    Solution was the the EPDM mesh reinforced with fabric covering top hoses I commissioned with an OE hose maker a few years ago..   Sold by British Motor Heritage as  GRH 453.  
 

It’s a new rubber hose.  Not a tight push on fit.  I’d say easy push on.  I think I’ll order another, even though this is new.  And get the wire clips which might help instead of the jubilee clips.  Thanks.

[RobH]

45 minutes ago, Steven Whitaker said:

Ok.  Is it normal for the radiator cap to lift before the thermostat has opened?

No. Under normal conditions the radiator cap on a TR  four-pot engine should never lift.  It is there to raise the boiling point of the coolant to above 100ºC by slightly pressurising the system - boiling point is 111ºC with a 7 lb cap so the cap should not lift until that temperature has been exceeded.

If the thermostat doesn't open when it should at around 80ºC, there is no coolant circulation through the radiator and the engine will overheat . If the temperature exceeds 111ºC, steam will be generated that will further pressurise the system and the cap will then lift.  

The cap might also lift at lower temperatures if the radiator has been over-filled. Water expands as it heats but is not compressible  and if there is no air above it to be compressed, the cap will lift to vent the excess water.   ( That is how a system with an expansion bottle works, as that sort of radiator is designed to be filled to the brim - in that case the expelled water is caught in the expansion bottle and is sucked back into the radiator as it cools )

 

Edited May 3, 2025 by RobH

[Steven Whitaker]

2 hours ago, RobH said:

No. Under normal conditions the radiator cap on a TR  four-pot engine should never lift.  It is there to raise the boiling point of the coolant to above 100ºC by slightly pressurising the system - boiling point is 111ºC with a 7 lb cap so the cap should not lift until that temperature has been exceeded.

If the thermostat doesn't open when it should at around 80ºC, there is no coolant circulation through the radiator and the engine will overheat . If the temperature exceeds 111ºC, steam will be generated that will further pressurise the system and the cap will then lift.  

The cap might also lift at lower temperatures if the radiator has been over-filled. Water expands as it heats but is not compressible  and if there is no air above it to be compressed, the cap will lift to vent the excess water.   ( That is how a system with an expansion bottle works, as that sort of radiator is designed to be filled to the brim - in that case the expelled water is caught in the expansion bottle and is sucked back into the radiator as it cools )

 

Ok, thanks.  I’m learning.  So is it worth refitting the hose and trying again with the 7lb cap?

[Z320]

In my opinion new hoses must fit tight.

I use them from Bastuck, they are so tight, I must put them in hot water to get them „soft“.

That‘s the way it must be

[Ralph Whitaker]

9 hours ago, Steven Whitaker said:

Ok, thanks.  I’m learning.  So is it worth refitting the hose and trying again with the 7lb cap?

Yes, as you should have halved the pressure in the system. Also check that the cap is the correct length for the TR radiator. If it still pressurises and blows the hose again or the cap you could have a head gasket problem.

Ralph

[Jase]

You may have done this already but why don't you flush the system before you go any further, pop a hose pipe on one side and flush the water right through, test and then add the appropriate antifreeze. At least you know it will flow through.

 

[Steven Whitaker]

Just now, Jase said:

You may have done this already but why don't you flush the system before you go any further, pop a hose pipe on one side and flush the water right through, test and then add the appropriate antifreeze. At least you know it will flow through.

 

Thanks.  The engine has been fully flushed out at the rebuild stage.

[Steven Whitaker]

1 hour ago, Ralph Whitaker said:

Yes, as you should have halved the pressure in the system. Also check that the cap is the correct length for the TR radiator. If it still pressurises and blows the hose again or the cap you could have a head gasket problem.

Ralph

Ok.  The cap is off my dad’s TR so will try it.  Thanks.

[Jase]

49 minutes ago, Steven Whitaker said:

Thanks.  The engine has been fully flushed out at the rebuild stage.

Great so that deals with any issues with circulation. Hopefully should be straightforward. I had a lot of issues with radiator caps with my Spitfire. I eventually went back to an old one I had on my shelf. The quality of new caps isn't good.

[Z320]

Hi, believe it or not, but very simple:

the pressure in the cooling system is NOT caused by the rad cap, it „only“ limits it.

The pressure is caused by two issues:

1st:

the temperature of the coolant —> as long it is below 100°C you have no noticable steam pressure

2nd:

the amount of air remaining in the colling system to be compressed by the expanding coolant,

—> more air keeps the raise of pressure low

—> no air pops the pressure up quickly

For example:

I drive my 4A with a 13 PSI cap, with about 1.3 l air in the rad and thermostat housing + the first 1,000 km of this year always below 81-84°C.

The max pressure in the rad was always below 7 PSI

I hope that helps

Ciao, Marco

[Steven Whitaker]

Fun day in the garage today!  I removed the water pump housing to inspect the spigot where the pipe kept blowing off, and found it to be tapered the wrong way.  When I fitted the hose and tightened the jubilee clip it was forcing the hose off the spigot.  So I ground a little off the neck of the spigot to reverse the taper and cleaned it up.  Before refitting the hose on again I tried the hose on again and it appeared to have the desired effect.

I then refitted everything and fitted the 7 lbs radiator cap off my Dad’s TR4a.  I refilled with water right up to the brim with the heater valve open.  I ran the car for a minute then topped it up again with water.  (Not using coolant yet as it’s a just a waste at this stage.

I started the car and brought it up to temperature slowly.  The hose stayed put.  The car temp gauge crept past normal and the top rad hose got hot. So I think that means the thermostat is opening so that’s good.  However, The temp carried on rising and the fan didn’t kick in.  (I have fitted a Revotec fan with an inline sensor.) The fan didn’t kick in and I noticed the expansion bottle was filling.  The temp gauge was almost into the red so I stopped the engine.  The bottle was almost full.

The bottom radiator hose was cold.  The fan never kicked in, and as it cooled it pulled all the fluid from the bottle back into the engine which I assume is good.  The hose didn’t blow off throughout.

So, how does all that sound?  I’m thinking I need to check the fan wiring.  The sensor is set to the coldest setting for the fan, but nothing! 

I’d appreciate any comments on progress and what to do next please folks.

Thanks, Steven.

 

 

 

[BlueTR3A-5EKT]

45 minutes ago, Steven Whitaker said:

Fun day in the garage today!  I removed the water pump housing to inspect the spigot where the pipe kept blowing off, and found it to be tapered the wrong way.  When I fitted the hose and tightened the jubilee clip it was forcing the hose off the spigot.  So I ground a little off the neck of the spigot to reverse the taper and cleaned it up.  Before refitting the hose on again I tried the hose on again and it appeared to have the desired effect.

I then refitted everything and fitted the 7 lbs radiator cap off my Dad’s TR4a.  I refilled with water right up to the brim with the heater valve open.  I ran the car for a minute then topped it up again with water.  (Not using coolant yet as it’s a just a waste at this stage.

I started the car and brought it up to temperature slowly.  The hose stayed put.  The car temp gauge crept past normal and the top rad hose got hot. So I think that means the thermostat is opening so that’s good.  However, The temp carried on rising and the fan didn’t kick in.  (I have fitted a Revotec fan with an inline sensor.) The fan didn’t kick in and I noticed the expansion bottle was filling.  The temp gauge was almost into the red so I stopped the engine.  The bottle was almost full.

The bottom radiator hose was cold.  The fan never kicked in, and as it cooled it pulled all the fluid from the bottle back into the engine which I assume is good.  The hose didn’t blow off throughout.

So, how does all that sound?  I’m thinking I need to check the fan wiring.  The sensor is set to the coldest setting for the fan, but nothing! 

I’d appreciate any comments on progress and what to do next please folks.

Thanks, Steven.

 

 

 

Has your radiator cooling fan got an override switch?   If so turn it on once the engine has started.    The temperature sensor might need adjusting.  
 

is this a brand new never run before engine.   It’s going to run hot at start up if that is the case 

 What Condition is the radiator?    

When filling a TR with water you only need to just cover the fins/tubes that you see inside the radiator filler neck.  About an inch down from the bottom of the neck to the water level is usual.    This is when cold.   As water heats it expands and fills the air space you have left.   As your thermostat looks like it has a jiggle pin or vent valve the following is probably not relevant as the water level should be equal either side of the thermostat.
 
At the filling stage with the radiator cap removed I would squeeze the lower rubber radiator hose to ‘burb’ any trapped air.   This is my method with sidescreen cars and not how Marco will advise with TR4A.   My friend failed to do this on his car after fitting the radiator and the car disappeared in a cloud of steam within 10 minutes of starting.  I also have a bleed valve fitted in the thermostat housing on my engine, again my personal preference.  

Edited May 4, 2025 by BlueTR3A-5EKT

[Steven Whitaker]

1 hour ago, BlueTR3A-5EKT said:

Has your radiator cooling fan got an override switch?   If so turn it on once the engine has started.    The temperature sensor might need adjusting.  
 

is this a brand new never run before engine.   It’s going to run hot at start up if that is the case 

 What Condition is the radiator?    

When filling a TR with water you only need to just cover the fins/tubes that you see inside the radiator filler neck.  About an inch down from the bottom of the neck to the water level is usual.    This is when cold.   As water heats it expands and fills the air space you have left.   As your thermostat looks like it has a jiggle pin or vent valve the following is probably not relevant as the water level should be equal either side of the thermostat.
 
At the filling stage with the radiator cap removed I would squeeze the lower rubber radiator hose to ‘burb’ any trapped air.   This is my method with sidescreen cars and not how Marco will advise with TR4A.   My friend failed to do this on his car after fitting the radiator and the car disappeared in a cloud of steam within 10 minutes of starting.  I also have a bleed valve fitted in the thermostat housing on my engine, again my personal preference.  

Hi Peter,  Thanks.

I had the radiator re-cored.  The bottom hose where the sensor is was cold!  Yes it’s a newly built engine, with all new pistons, liners, big ends and mains and I have running in oil in it.  There isn’t an over ride switch on the fan but thinking now I need to fit one and have another go.

 Ur why was the bottom hole cold?  Air?

Cheers, Steven.