Underbonnet heat

[EliTR6]

The new manifold and exhaust are nearly on. I need to spend some time fiddling with the back box so the centre pipe clears the chassis plate and have ordered a couple of missing U-clamps for the Y piece.

 

Starting the car up yesterday evening, no leaks as far as I can tell. The manifold (not lagged or coated - yet) gives off a huge amount of heat. The new hi-torque starter motor sits right next to it. Is this the only component at risk or could other parts go wrong due to the heat? Is there any risk of fire? I would have thought not but you never know...

 

I'll definitely be keeping a fire extinguisher on the passenger seat when I take the car for a spin!

[foster461]

The new manifold and exhaust are nearly on. I need to spend some time fiddling with the back box so the centre pipe clears the chassis plate and have ordered a couple of missing U-clamps for the Y piece.

 

Starting the car up yesterday evening, no leaks as far as I can tell. The manifold (not lagged or coated - yet) gives off a huge amount of heat. The new hi-torque starter motor sits right next to it. Is this the only component at risk or could other parts go wrong due to the heat? Is there any risk of fire? I would have thought not but you never know...

 

I'll definitely be keeping a fire extinguisher on the passenger seat when I take the car for a spin!

 

There is always a risk of fire when you have that much fuel flowing right over the exhaust manifold. You should see what happens with dcoe's if you pump the gas pedal too often before starting the motor. Definitely a good idea to keep an extinguisher on board and a requirement at many of the shows I go to. As you say the starter motor and its wiring will also get very hot as they do with the cast manifold.

 

Also excessive heat is not good for the induction system so I often see people wrapping the headers with some heat shield material or fitting heat shoeld to carbs. Not sure if doing things like ceramic coating are just cosmetic or if that also reduces heat radiation or if heat shielding is even an issue with the PI throttle bodies.

 

Stan

[EliTR6]

There is always a risk of fire when you have that much fuel flowing right over the exhaust manifold. You should see what happens with dcoe's if you pump the gas pedal too often before starting the motor. Definitely a good idea to keep an extinguisher on board and a requirement at many of the shows I go to. As you say the starter motor and its wiring will also get very hot as they do with the cast manifold.

 

Also excessive heat is not good for the induction system so I often see people wrapping the headers with some heat shield material or fitting heat shoeld to carbs. Not sure if doing things like ceramic coating are just cosmetic or if that also reduces heat radiation or if heat shielding is even an issue with the PI throttle bodies.

 

Stan

 

Thanks Stan. The plan was to test drive it this weekend and then remove the manifold to get it ceramic coated if it was getting too hot. Bring on london traffic in summer...

 

Anyone running PI out there with a non-coated or lagged sports/race manifold?

[jstone]

Thanks Stan. The plan was to test drive it this weekend and then remove the manifold to get it ceramic coated if it was getting too hot. Bring on london traffic in summer...

 

Anyone running PI out there with a non-coated or lagged sports/race manifold?

 

 

Yep, I am and I have had no problems to date and that is a years worth of motoring. I hope that is now not the kiss of death

 

Jeremy

[chrismitchell]

Yup. Mines been running for 7 years no problems in some incredibly hot conditions & traffic jams. Has original engine driven fan to keep air movement. No electric fan - uses Forlife coolant instead.

[Goswell]

If my car gets hot in traffic then it missfires which I put down to cavitation.

The electric fan normally solves my problem but I'm running a standard engine config.

Personnally I'd do everything to reduce heat, not increase it.

[marvmul]

The exhaust manifold gets much hotter when the ignition has too little advance, especially when the engine is idling. Probably you will notice that the exhaust manifold will be cooler if you keep the rev's at say 2000 rpm, even when the ignition advance is spot on. But I would check the ignition advance anyway. I think this is no reason to wrap the manifold, but a heat shield on the starter and also the alternator is very useful to prevent early failure.

[EliTR6]

Thanks for the replies chaps.

 

Something like this could do it, bit pricey though... Will look on ebay.

 

http://www.demon-tweeks.co.uk/products/Pro...pcode=DEI010402

[Richard Crawley]

I've run a SS Phoenix on a stage 2 engine for nearly 5 years without any lagging & without any problem. The 6 has always been hot under the bonnet but unless you seriously modify the motor, it will give out the same heat with an SS manifold as it did with the original cast iron one! Cast iron will take longer to heat up & cool down but on a given run of, say, more than 30 minutes the under bonnet temperature will be exactly the same as it was before. Apart from the perceived kudos it seems to give, I see absolutely no point in lagging let alone ceramic coating the manifold of what is otherwise a standard or even mildly tuned engine!

[Guest ntc]

I've run a SS Phoenix on a stage 2 engine for nearly 5 years without any lagging & without any problem. The 6 has always been hot under the bonnet but unless you seriously modify the motor, it will give out the same heat with an SS manifold as it did with the original cast iron one! Cast iron will take longer to heat up & cool down but on a given run of, say, more than 30 minutes the under bonnet temperature will be exactly the same as it was before. Apart from the perceived kudos it seems to give, I see absolutely no point in lagging let alone ceramic coating the manifold of what is otherwise a standard or even mildly tuned engine!

 

Richard is correct it is a misconception that lagging was to reduce engine bay temp's although it does slightly it's purpose was to increase the manifold temp internally . However with any oil or fuel leak it can act as a wick.

Neil

Edited October 6, 2008 by ntc

[Mike G]

Check this site, seems a good price.

http://merlinmotorsport.co.uk/product_info...medium=Shopping

 

Mike g

[88V8]

I have a 6/2 tubular manifold. No trouble with underbonnet heat in general, the Kenlowe fan copes well (other than drawing too much current but then it is 30 years old).

I lagged about 6" of the manifold pipe (one of the six pipes, that is) that runs next to the starter, and also lagged the starter itself.

 

As regards induction, it's true that the manifold runs at the same temp as the cast one, but it loses more heat into the underbonnet because the tubular manifold has a larger surface area.

As NTC said, this is also the reason that tubular manifolds are sometimes lagged in performance applications, because as the exhaust gas loses heat it slows down and this impairs the scavenging effect of a well-tuned exhaust system. However, I suspect it's pretty theoretical in average road use.

 

The important thing is that as the PI system draws its air from the cool front of the car, there should be no power loss due to heating of the induction air by manifold heat emission.

 

Ivor

[Richard Crawley]

The important thing is that as the PI system draws its air from the cool front of the car, there should be no power loss due to heating of the induction air by manifold heat emission.

Also the main reason why those stubby K&N's fitted directly onto the intakes that are also very fashionable are really not such a good idea!

[Tom Fremont]

No argument about the need to ceramic coat for heat reasons, but they claim some noise reduction too. I've got Phoenix types on both my cars and both are ceramic coated, giving reduced surface temperature ( the insulating property results in a larger delta T ), less noise ( theoretically - not proved this so am interested in Eli's before/after report ) and better appearance - no weld discoloration, etc.

 

I recommend it

[Tony Millward]

Also the main reason why those stubby K&N's fitted directly onto the intakes that are also very fashionable are really not such a good idea!

 

 

Whoops!!...was going to fit the K&N's to mine but will go back to the plenum and cold airflow... Thanks Richard, the more I read, the more I learn...

 

Cheers

 

Tony

[Crownwheel]

Also the main reason why those stubby K&N's fitted directly onto the intakes that are also very fashionable are really not such a good idea!

 

I was also concerned about underbonnet temperatures reducing power before deciding on the K & Ns so I located a remote temperature sensor around various locations where the filters would be located.

Sitting in traffic the temperatures reach about 60 Deg C but when travelling at 60 the temperature is no greater than 2 Deg C above ambient.

A (very) rough calculation on the amount of air entering the engine compartment works out at over 3 cubic meters per second. I would expect this volume to scavenge alot of hot air.

No radiator air duct is fitted so a significant amount of air bypasses the radiator.

This also explains why even after a fast thrash if I open the bonnet I can rest my hand on the alloy finned rocker cover for at least 30 seconds before the heat in the block makes things a bit uncomfortable.

 

I am sure a thermal engineer in our number could do the sums but empirically there seems no need to be too concerned about air temperature power loss at least if you are not sitting in traffic.

 

Also to follow the original thread, I have never had any overheating problems in the 6 even when stuck in French traffic jams for over an hour at 30Deg plus ambient. If anything I often worry about the engine running too cool.

 

John

[WELLSY]

I have triple webers ,ss racetorations 6-2-1 manifold and exhaust, and a heat shield. The car has always struggled to start when hot. Black smoke blows out the back and the engine splutters for the first few seconds then clears when moving.

Could this be caused by the heat from the exhaust heating the fuel in the pipes as it runs alongside it under the car and also in the carbs at standstill?

The float levels have been checked and the fuel pressure is around 2 psi.

[88V8]

I was also concerned about underbonnet temperatures reducing power before deciding on the K & Ns so I located a remote temperature sensor around various locations where the filters would be located.

Sitting in traffic the temperatures reach about 60 Deg C but when travelling at 60 the temperature is no greater than 2 Deg C above ambient.

A (very) rough calculation on the amount of air entering the engine compartment works out at over 3 cubic meters per second. I would expect this volume to scavenge alot of hot air.

No radiator air duct is fitted so a significant amount of air bypasses the radiator.

I am sure a thermal engineer in our number could do the sums but empirically there seems no need to be too concerned about air temperature power loss at least if you are not sitting in traffic.

That's very interesting.

I found that underbonnet heat had a significant detrimental effect on the V8 in my old Landy, it greatly improved in power when I fitted two vents to the bonnet above the carbs.

I've also noted that pretty well all manufacturers take care to duct cold air from the front of the car, including those making high-end sports cars.

Hence my aversion to taking air from above the exhaust manifold.

Especially as the engine bay has no outlet vents, so air has to exit underneath, and I would have expected little active interchange with the hotter air near the throttle bodies.

However, as you have taken the trouble to measure, I do not doubt what you say.

 

I am also surprised that you are able to run at speed with no rad cowl. To me, this is another no-no, as much of the air will take the lazy route and enter the engine bay having bypassed the rad.

Have you ever run with the cowl in place, did you notice any difference in the cooling?

 

Ivor

[Crownwheel]

I am also surprised that you are able to run at speed with no rad cowl. To me, this is another no-no, as much of the air will take the lazy route and enter the engine bay having bypassed the rad.

Have you ever run with the cowl in place, did you notice any difference in the cooling?

 

Ivor

 

Ivor.

 

Recently fitted a radiator cowl (nasty cardboard thing that gets soggy in the wet) to tidy the engine bay and have noticed no difference in the underbody temp at speed (my remote sensor) but the engine temp is even cooler than normal...it barely gets off the endstop! (presumably more air directed through the radiator?) Nothing wrong with the guage as it even gets up to (almost) halfway in jams. Electric fan by the way.

Lots of air should spill around the side of the cowl as its not too deep on the intake side so I am not surprised about the cool (relatively) engine bay temperature at speed.

So I am more worried about running cool rather than anything else. The TR is the coolest running car I have ever owned. (You can interpret this two ways)

Advice on "overcooled" cars sought.

 

John

[Alec Pringle]

Hi John,

 

I've driven a lot of TRs in 40 years, and my experience has been that temp gauges usually err on the side of under-reading, as in the engine is a tad warmer than the gauge might suggest.

 

The rad cowling makes very little difference to the underbonnet air temperature, but it does make a considerable difference to the radiator efficiency. At the risk of asking the obvious, have you tried adjusting the electric fan control to take into account the increased radiator efficiency ? Yes, I realise that adjusting the fan 'stat perhaps shouldn't be necessary, but personal experience suggests that it is !

 

Cheers,

 

Alec

[Richard Crawley]

The under bonnet temperature may well be within acceptable limits as far as the motor is concerned but what’s important for efficient combustion is lots of nice cool air, the cooler & moister the better; havn't you ever noticed how much better the car seems to go on cold damp autumn mornings!

 

That's very interesting.

I found that underbonnet heat had a significant detrimental effect on the V8 in my old Landy, it greatly improved in power when I fitted two vents to the bonnet above the carbs.

I've also noted that pretty well all manufacturers take care to duct cold air from the front of the car, including those making high-end sports cars.

 

I'm with Ivor on this one.

[88V8]

Recently fitted a radiator cowl (nasty cardboard thing that gets soggy in the wet) to tidy the engine bay and have noticed no difference in the underbody temp at speed (my remote sensor) but the engine temp is even cooler than normal...it barely gets off the endstop! (presumably more air directed through the radiator?) So I am more worried about running cool rather than anything else.

Advice on "overcooled" cars sought.

Mmmm yes, the cowl is important in making the rad - and any oil cooler in front of the rad - work properly. Mine gets just over the mid-point in traffic, before the electric fan pulls it down again.

 

You could control the running temp with a rad blind. This was a popular accessory for winter running in the 60s, and wouldn't be hard to rig up. I have one on the shelf, destined for my Landy, one day...

It's a spring-return fabric blind - like a window blind - located in front of the rad, at the bottom, you operate it with a cord from the cockpit, pull it up and it blanks all or part of the rad depending how far you pull.

In the 20s, some upmarket cars had thermostatically controlled shutters to serve the same function. I guess you could emulate that with louvres and a greenhouse wax-powered opener.

Scope for Heath Robinson here

 

Ivor

Edited October 10, 2008 by 88V8

[Geoff Davies]

I was also concerned about underbonnet temperatures reducing power before deciding on the K & Ns so I located a remote temperature sensor around various locations where the filters would be located.

Sitting in traffic the temperatures reach about 60 Deg C but when travelling at 60 the temperature is no greater than 2 Deg C above ambient.

A (very) rough calculation on the amount of air entering the engine compartment works out at over 3 cubic meters per second. I would expect this volume to scavenge alot of hot air.

No radiator air duct is fitted so a significant amount of air bypasses the radiator.

This also explains why even after a fast thrash if I open the bonnet I can rest my hand on the alloy finned rocker cover for at least 30 seconds before the heat in the block makes things a bit uncomfortable.

 

I am sure a thermal engineer in our number could do the sums but empirically there seems no need to be too concerned about air temperature power loss at least if you are not sitting in traffic.

 

Also to follow the original thread, I have never had any overheating problems in the 6 even when stuck in French traffic jams for over an hour at 30Deg plus ambient. If anything I often worry about the engine running too cool.

 

John

 

John, you answer the question with regards to the 2 Deg C above ambient in that is where the K&N will take its air from as opposed to the cooler air coming from in front of the car that is effectivly moving so will be lower than ambient and depending on speed by even more.

 

I have a modified engine and extractor manifold but also upgraded the radiator to one I specified (see previous post) and that more than copes with the increased heat although the inside of the car is much hotter now and I may consider putting insulation on the bulk head.

 

 

Geoff

[Crownwheel]

Hi John,

 

I've driven a lot of TRs in 40 years, and my experience has been that temp gauges usually err on the side of under-reading, as in the engine is a tad warmer than the gauge might suggest.

 

The rad cowling makes very little difference to the underbonnet air temperature, but it does make a considerable difference to the radiator efficiency. At the risk of asking the obvious, have you tried adjusting the electric fan control to take into account the increased radiator efficiency ? Yes, I realise that adjusting the fan 'stat perhaps shouldn't be necessary, but personal experience suggests that it is !

 

Cheers,

 

Alec

 

Hi Alec

The electric fan is adjusted OK and comes on in traffic when indicated temperature gets close to "halfway". Seems repeatable. Fan never comes on when running. I agree that these guages err on the cold side in their readings. I am sure I have a few old ones (I have been the terminal owner of many Triumphs) in the cellar somewhere....must dig them out and compare readings.

 

Ivor

Radiator blinds. I remember them. I used to have to stuff bits of cardboard in front of the radiator when I was going through my Spitfire phase when a bit younger. Only way I could have remotely warm feet.

Good point though. I may apply some judicially small plates in front of the radiator to see what effect it has. On the other hand, the greenhouse won't be needing its window thermostat for the next 6 months....!

Sorry for seemingly hijacking a hi temperature thread into a low temperature one.

Thanks for all the suggestions.

 

John

[Alec Pringle]

Hi John,

 

It's just possible then that you might have a sticking thermostat - as in the water thermostat, not the one on the fan ?

 

If the beggar isn't closing fully, engine temperature will remain low and the fan will operate only after a period stuck in traffic. A problem I suffered last year on one of our Rovers, made even more mysterious when a replacement 'stat didn't solve the problem - the new 'stat had the same problem as the old ! A second replacement 'stat cured the problem.

 

Cheers,

 

Alec