Underbonnet heat

[John Morrison]

hi all, 

Have  a fellow group member, whose TR6 generates considerable amounts of underbonnet heat,

so much so that when you raise the bonnet it notcibly hits you in the face, 

I've certainly never known another TR get as hot as this. engine temp is pretty normal, no overheating.

Proboblem is such that if say he waits to turn Right for a min or two, the car can bog down when he asks it to go.

 

Looking around the engine bay, it has a tubular six branch manifold, thats not lagged, I'm thinking this is a starting place?

Any thoughts?

 

John.

[RogerH]

Hi John

some sort of insulation on the exhaust manifold would indeed help.

Does he still have the mechanical fan - if no then that may be part of the problem. The electric fans only turn ON when needed.
An oil cooler if fitted may pass more hot air rearwards.

 

Roger

[TR NIALL]

Either wrap the SS Manifold or swap for standard cast type,always use the override Switch for electric fan when stationary or in heavy traffic,when parking up after a long hard run pop the Bonnet open to allow heat to release for easier starting.

[cp25616]

Good advice Niall, change back to cast manifold and have an override switch for the electric fan.

Alan G

[Z320]

Hi,

of cause it is hot under the bonnet with the engine off after a run,

and standing on the opened bonnet this is the only way we can notice this.

But there is no special heat under the bonnet with the engine running or the car driving.

I, and years ago a TR friend, had thermometers fixed under the bonnet showing the temperature is no issue.

This is why I see no reason to worry or do anything.

Ciao, Marco

[Mike C]

I've also got a tubular six branch manifold and a mechanical fan and I don't have this problem , and there are probably hundreds of cars like mine that also don't have the problem.

I guess my engine compartment temperature gets to 40 to 50 deg C based on running the car with the transmission tunnel removed.

Is there anything else unique about this particular vehicle?

As to the hot under bonnet air bogging the engine down, there is a lot to be said for the original TR6 cold air inlet system.

[john.r.davies]

Wrapping a steel manifold can cause a corrosion problem.     I did this a while ago, and when the wrapping began to look worn and tatty (it will!) I took it off.  Underneath the pipes were significantly thinned, not by red rust, but by long flakes of blue-black corrosion.   I have presumed that these were ferrous oxide (red 'rust' is ferric ) which has less oxygen in the compound, presumably because of the wrapping.

Your friend could try ceramic coating, which is claimed to be effective, but I find that difficult to believe.    The Space Shuttle had ceramic coating to protect its aluminium structure from melting due to the heat of re-entry.  The temperature difference was about the same as between exhaust gases and room temp, and need SIX INCHES of ceramic foam to do the job!   Exhaust coating is about one millimetre.

John

[TRTOM2498PI]

I think he has problems elsewhere, based on the above.

1. Is it a new engine ?

I run this competition exhaust manifold, with zero coating or anything wrapped around the tubes, and have driven in many climates abroad, and has sat in traffic, without any issues whatsoever.

[Steve-B]

John, has a previous owner installed any form of panel under the engine bay which was the rage in some circles in the late 80s/early 90's to supposedly "increase aerodynamics". If so in many cases that could create mini-rolling ovens. Like others here, I'm a bit perplexed by the question as I too have been in a variety of heats and never encountered such a heat-rush as you're describing.

But I'm sure there's longer term smarter owners here that know more than I 😉 that'll be along soon

[Harbottle]

Does the bonnet have any sort of sound deadening material fixed to it.

[Magz]

He can always add hood louvers.

Note: this is a ChatGPT image. I haven't done this to my car...yet.

[Z320]

Exhaust manifold and exhaust pipes are not made to be wrapped and get hottern than needed.

Browse the internet and find examples very easy....

 

 

[john.r.davies]

Goah, Z320!    Mine were not as bad as that, but the blue/black flakes were exactly the same! Distinctly different form.of corrosion on the anoxic wrapped manifold.

John

[Paul Hig]

John

6s can tend to run hot in the engine bay which is why they can suffer from fuel vaporisation in the injector lines when stationery. Braided injector lines can make this worse. 

[CK's TR6]

IDK, I live in Phoenix AZ and drive my TR6 year round. I will admit anything over 108f outside it isn’t much fun but if you are moving along, it is tolerable.  I have a ceramic coated header, 9.9CR, and all the rest. My electric fan runs whenever the thermo switch in the radiator says to. Even at 100f outside, I can pull into my garage and the fan is not running. A few minutes after shutdown it will come on. The engine compartment, if hot, will cool from that. I suspect that there is some thermo siphon effect for the engine until the thermostat closes.  I feel that the engine compartment on my other cars are far hotter than the TR. 

[Z320]

I’m conviced on any TR there is no thermo siphon effect on the engine / rad circut if no  special bleeding system is installed.

This is because on any standard TR there is air on top of the circut when the engine is off.

But - I‘m also convinced this is not needed.

Ciao, Marco

[John Morrison]

20 hours ago, TRTOM2498PI said:

I think he has problems elsewhere, based on the above.

1. Is it a new engine ?

I run this competition exhaust manifold, with zero coating or anything wrapped around the tubes, and have driven in many climates abroad, and has sat in traffic, without any issues whatsoever.

Possible that you are correct Tom, 

the car runs well, with good MPG, it might be a tad lean, where else should look?

John.

[stuart]

3 hours ago, John Morrison said:

 it might be a tad lean, 

John.

And there you have it. That alone will cause a lot more heat. I bet if you revved it up in the dark that exhaust manifold will glow red.

Stuart.

[CK's TR6]

9 hours ago, Z320 said:

I’m conviced on any TR there is no thermo siphon effect on the engine / rad circut if no  special bleeding system is installed.

This is because on any standard TR there is air on top of the circut when the engine is off.

But - I‘m also convinced this is not needed.

Ciao, Marco

Marco, I agree but I put a fitting on the top of the thermostat housing and fully evacuated the system.  On my 76 that has the top hose come straight forward, I measured the coolant level in that horizontal section as half full prior to putting in the fitting.  When I change the coolant, I have one of those funnels that seal onto the radiator, with the fitting open on the top of the thermostat, it gives a place for the air to come out. Also, I removed the standoff from the head for the heater control valve. This places that circuit lower in the system. After a good purge run getting all the air in the system to the top, I let the engine fully cool and then remove any remaining air in the system.

[Z320]

This I mean with special.

But not needed anyway IMO

Edited Thursday at 09:17 PM by Z320

[jerrytr5]

I think I might start checking the temp sender, gauge & thermostat. Maybe it is overheating.

Jerry

[Mike C]

Maybe do a quick check around the engine bay  with an infra red thermometer - it will tell you if your radiator temps are in the ball park and might find any spots of excessive heat.

[super6al]

On 5/7/2026 at 11:19 AM, stuart said:

And there you have it. That alone will cause a lot more heat. I bet if you revved it up in the dark that exhaust manifold will glow red.

Stuart.

+1 and check the ignition timing isn't too far advanced