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Re: Engine running hot at idle

PostPosted: Fri Jul 13, 2018 9:55 am
by Robbie693
Surely the fact that William's fan has cut in proves that the coolant is at the temperature specified by the Otter switch (or whatever sensor is fitted)?

I've searched for years to find a reason why some cars, mine included, run hot and I think the theory of partially blocked water galleries due to sludge, silt, I even read sand from the original casting process, holds the most water(!)


Re: Engine running hot at idle

PostPosted: Fri Jul 13, 2018 10:22 am
by Craven
Just a passing thought, cylinder wall thickness. Do some blocks provide better distribution into the mass of iron with its air surface area. A thick cylinder wall will be less likely to have hot spots.
I have been staggered by the amount of casting sand washed out of some blocks must have something to do with it, just as well it stays put we have enough water pump problems as it is.

Re: Engine running hot at idle

PostPosted: Fri Jul 13, 2018 5:14 pm
by William2
I have a 82 degree thermostat fitted. The fact that the engine temp sits nicely at 82 on the gauge also gives me added confidence that the gauge is accurate. I am assuming that fitting a 74 degree stat wouldn't make any difference to the temperature climbing in traffic jams??

Re: Engine running hot at idle

PostPosted: Fri Jul 13, 2018 6:33 pm
by Donels
The symptoms you describe sound like slow circulation rather than insufficient cooling. When the engine speed increases and circulation rate increases the temp quickly comes down, pointing to circulation.

If the circulation is slow the radiator/fan cannot provide any more cooling at that flow rate, to increase the cooling rate either the flow rate needs to be increased or the airflow through the radiator needs to increase. IMO it points to an inefficient water pump. Popping the bonnet helps as it increases the airflow but the basic problem is low circulation.

Is the idling speed, hence pump speed too low?

I used to run a hot crossflow in a Westfield and they were notorious for overheating on hot track days. The solution was to fit a smaller water pump pulley, hence increasing the flow rate. These were readily available from Burton. Not sure if something similar is available for a twincam.

You also say it reaches 100 C. Is this a mechanical problem or a confidence problem? What temp would be normal?
You could just let it idle at home and see where it stabilises. If it sits happily at 100 C then why worry, if it continues to increase to say 110 C the maybe you have a problem.

My Elise dislikes traffic and the temp increases from a normal 86 C to 96 C in traffic even though the fan cuts in at 90 C. As soon as I increase engine speed the temperature drops back to 86 C. I put this down to the long circuitous cooling system. It gives me a problem but the engine doesn't seem to mind!

Re: Engine running hot at idle

PostPosted: Sat Jul 14, 2018 10:36 am
by Donels
Ignore what I wrote about crossflow mods it was completely wrong. It was a smaller crank pulley to slow the water pump down to prevent cavitation at high revs.

Re: Engine running hot at idle

PostPosted: Sat Jul 14, 2018 11:47 am
by Chancer
I thought that was probably the case, I did it to mine which meant I needed to fast idle in hot weather to keep the temp within limits.

I dodnt say anything because my memory is as capricious as yours :lol:

Re: Engine running hot at idle

PostPosted: Wed Feb 20, 2019 4:08 pm
by elanner
Not quite sure where to post this, but this thread seems to be the most recent about overheating.

Hagerty in the US sends out a regular newsletter about classic cars and the most recent discusses overheating of 1960s Mustangs: ... ting-issue

Obviously not pertinent to Elans, but this sentence struck me as a rational way to approach an overheating issue:

"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."


Re: Engine running hot at idle

PostPosted: Wed Feb 20, 2019 5:15 pm
by prezoom
Back in the middle 60's, I managed to purchase a Shelby AC 289 Cobra (CSX2176) by merely taking over the car payments. The unpleasantness in South East Asia had the previous owner being snatched up by the government. Having the Cobra and my S2 S7 at the same time, is something beyond my imagination today. The Cobra over heated at almost every occasion it was driven. At one point, it even pushed out a core plug during a vacation trip up the Pacific Coast. Nothing like trying to replace the core plug on the side of the road with a knock on hammer and a section of the jack handle. All the external tricks were tried with no improvement. It was during an overhaul, when I was attempting to clean out the block by removing the core plugs, that I found wire and sand in the water jacket at the rear of the block left over from the casting process. Picking away at what was blocking the water flow, eventually resulted in a significant amount of debris, more than half filling a one pound coffee can. After re-assembly, the engine never overheated again. That experience has had me picking around in the water passages of every engine that I have built since.

Re: Engine running hot at idle

PostPosted: Sat Mar 23, 2019 11:15 am
by Oldboldpilot
If your car runs fine with the ram air of driving but not when in slow traffic or stationary it is odds on to be the fan not delivering enough puff. The fan fitted to the very late series 3, series 4, Sprint, Plus 2 and Plus 2S was taken from a Smiths heater motor or off Colin Chapman's desc. It will deliver air in every direction with the exception of through the radiator. The only option is a modern fan in a plastic ring up against the core that delivers all of the air it produces through the core. We cant always hang onto originality, especially if it ends up in a cooked engine.

Image ... olex-fans/ ... -small-new