Heating Up When Stationary

[William2]

I know this subject has been discussed a lot but I thought I would seek some comments.
My S4 has a wide alloy rad with a single fan set up and everything else is as it should be i.e. bonnet foam, and shield under the rad and the correct air vent holes on the left hand wheel arch area. The engine has covered several thousand miles since rebuild and the coolant is free of any signs of rust/oil.
The temp gauge has been checked for accuracy and the car typically runs at about 80/85 degrees on the move.
The issue is that when the car is stationary after a few minutes the temp gauge starts climbing to over 100 degrees even if I keep the revs up to about 1500rpm. A while ago I stuck temp indicator strips all over the head, block and rad top to monitor the various areas. It would appear from these that the block, rad and head all seem to be fine at about 90 degrees but the strip on the area on the head near where the thermostat sits is showing up to about 105 degrees. The rad doesn't seem to be venting any coolant which is obviously a good sign so maybe there isn't any real overheating problem. Assuming the stick on strips are accurate they seem to give a good indication of hot spot areas which in my case only seems to be the thermostat head area.
Would I be correct in saying that as long as there is no loss of coolant then don't worry?? I just get a bit twitchy when the gauge keeps rising!! Any comments gratefully received.

[nmauduit]

is the thermostat operating as it should (you may try without)? I always drill one or two 3mm holes in my thermostat before installation, to make sure there is not a lock preventing heat transfer.

I assume the electric fan does work well and in the right direction... one should be enough with a clean engine cooling circuit (though I've installed a second one, for the odd summer track days) - there may be an issue causing poor pump efficiency... hopefully not the block being clogged with scale.

good luck !

[rgh0]

Radiant heat from the headers can cause the temperature sensor to read high, especially when sitting stationary as no cooling air flow. Given the system appears to be operating normally apart from the high sensor reading i would suspect this is the issue.

what sort of headers do you have and are they insulated or have ceramic coating to reduce radiant heat from them?

cheers
Rohan

[nmauduit]

again Rohan seems to have nailed a good lead, apparently stainless headers radiate even more, and once the bonnet is well sealed with foam it all adds up... which made me think of the 2 holes on the inner fender that should help push away the accumulated hot air (if the electric rad is on the carb side that would not help much stirring hot air) : you may want to check if the grill is not blocked, e.g. like after a respray...

[William2]

I have to admit that I do have a stainless exhaust manifold and had read previously that they radiate more heat than mild steel. I have put some lagging round the areas I can get to. I assume the new water pump is working ok because when revving the engine it doesn't bring the temp down. I assume that if I had any air locks they would have cleared by now. I might check to see if I had drilled an 1/8" hole in the thermostat or not but have always wondered if this is strictly necessary. I could try and fit another thermostat but I think the one fitted is working well. It just seems strange that the temp indicators that I have stuck in several places on the head/block all read ok except for the one on the thermostat housing. I wish in a way that I had fitted a mild steel manifold instead. Excessive heat build up under the bonnet seems to be the most likely cause.

[disquek]

Stainless is a better insulator and thus will radiate less heat then mild steel. You're better off with the stainless header.

As suggested, a ceramic coating will further reduce the heat from the header.

[William2]

I am sure that stainless is worse and produces more heat???

[disquek]

Metal, Metallic Element or Alloy Temperature Thermal Conductivity
Steel - Stainless, Type 304 20 14.4
Steel - Carbon, 1% 20 43

From: https://www.engineeringtoolbox.com/ther ... d_858.html

[awatkins]

If the radiant header heat were the issue, could you not verify that by simply opening the hood and then watching the temp come back down?

Suggest also you make sure there is no air in the system, since if there were I think it would tend to collect around the thermostat.

[69S4]

If the radiant header heat were the issue, could you not verify that by simply opening the hood and then watching the temp come back down?.

My S4 has the same issue and opening the bonnet does indeed bring the temp back down. Not that practical in traffic though. Achieving the same result with the bonnet shut - even with a new electric fan - has been something I've not solved

[collins_dan]

My S4 always did the same thing. I went with 2 8" fans that are very efficient, but blow really hard and mounted them on the front. I know the whole argument for mounting on the back, but they blew so hard, they made me hot in the car. Now the car can sit and never go over 200F even when its 90F outside. Dan

https://www.summitracing.com/search/dep ... perma-cool

[lotusfan]

William2

Have you got the original radiator fan - the bent tin and heater fan motor version - or a more modern plastic version?

What turns the fan on? Is it done manually or automatically?

the temp gauge starts climbing to over 100 degrees even if I keep the revs up to about 1500rpm.

Running the engine faster will increase the heat load, not improve the cooling.

Maybe the solution is simply to reduce the thermostat operating temperature?

[elanner]

Gee - this week seems to be cooling fan week! If everybody is having temperatures like we've been having in New England it's not surprising.

Anyway, from William's original thread on this: viewtopic.php?f=39&t=42080, I still like the comment I found in a Hagerty article on overheating:

"The answer here depends on how the car is running hot. If it?s hot even while cruising down the highway, it?s a water-flow issue. If it?s cool while in motion and only hot while idling in traffic, it?s an airflow issue."

It stands to reason that holes in the wing, foam under the bonnet, a blanking panel under the radiator, etc. will do nothing on their own when the car is stationary. Air has to be moving and, with some Elans, a lot of it.

You know the temperature is fine when the car is moving, so I would upgrade to two seriously powerful fans.....

Nick

[disquek]

This is where I was thinking a small (like a 4" ATV) fan in the wheel well pulling air through the vent would help get that stagnant hot air out of the engine compartment.

I'm also thinking that sealing around the radiator might help in traffic, because it prevents the hot air in the engine compartment coming back forward to in front of the radiator and through the fan again. This seems like a shorter path than pulling fresh air through the grill.

-Kyle

[MarkDa]

This may seem a silly question but are you sure the fan is working?
With the rad edges sealed you probably don't need it on the move.
You could perhaps try a lower temperature switch to get it to turn on earlier when you you slow down.