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Gut the Thermostat? YES or NO


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Hi Guys,

I currently have the plenum off for some routine maintenance; new plugs, leads, coilpacks etc.

and whilst the plenum is off, I cannot deside whether to to simply replace the Thermostat or perform the "Gutting" proceedure

as noted in various other threads.

I've not had any problems with overheating and the engine runs fine, but personally hate the way that the engine runs

up to 110Deg before the fans kick in and its general temp when in traffic always feels like a cause for concern.

This high temp constantly makes me nervous when driving in built up areas and I'm suprised that the fans dont trip on and off

at more "Normal" 90Deg back to 80Deg and I would personally like it to run at 80Deg all the time.

So; according to other threads, rumor would have it, that if you gut the thermostat, the car runs at 70-80 all the time.

Has anyone done this mod, that can confirm if its true or not?

I'm in the UK and although I use the old girl as a daily driver, she is not used in the winter, so I cant see warm up times being too much trouble

What's your thoughts, YES or NO?

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No. Wouldn't even consider it. Fix the problem properly, the car didn't behave like that when it left the factory.

When was the last time you inspected your radiator for blockages and/or generally falling apart?

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  • Gold FFM

I'm with Graham. It's there for a reason, and gutting it can cause engine wear due to slow warm-up, and only masks the problem, whatever it may be.

British Fart to Florida, Nude to New York, Dunce to Denmark, Numpty to Newfoundland.  And Shitfaced Silly Sod to Sweden.

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If your fans are turning on at too high a temperature, it's because the temperature switch for the fans is set too high. It's nothing to do with the thermostat. Get an adjustable switch.

S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE


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I have to concur. I currently don't have any sort of cooling issue (knock on wood). Engine purrs right at 80-85 while driving, and sitting in traffic will only climb to 100 before the fans kick on and drop it back down to 80. Keep in mind that gutting the thermostat results in all the water in the cooling system continuously circulating and will result in longer warm up times and attribute to less engine efficiency (open loop until operating temp is achieved), greater fuel consumption and a less efficient heater during winter since the water is constantly being cooled by the main radiator rather than being "forced" through the cabin heater circuit by closing the path to the radiator via a working thermostat.

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Agree that the fan should come on at 100° certainly 110° is too high.

The thermostat will be chosen for optimum operating temp, making it run 10-15 degree lower could effect efficiency.

Plus without the thermostat it could throw error codes on cold days from not warming up quick enough? Cant remember the number but if the engine doesnt get to 40° within a certain time then you will get a warning light.

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  • Gold FFM

isn't the radiator-fan system on the V8 switched by the ECM in general ?! *it's an wrong set switch, get an adjustable* as in the advice above would not really help, would it ?! -until you rewire the system on that point. And what you see on the dial in the instrument cluster is the water temp on the sensing point on top of the block, not the exact water temp in your radiator... . So as long as the Thermostat is performing like it should there is nothing to worry-(test this with Thermostat out, put it in a cooker with thermometer and watch out for opening gap distance).

Test your cooling water for concentration of mixture, as it is not only there as a protection against ice build ups -it works also against rust and 'mud' resting in the small pipes in the radiator-mesh. Other point is , as mentioned by the other posts: check for free flow of air across the fins in the mesh.. . If you would have an problem with an not spinning water-pump impeller, think you could note that already by an odd sound. So if there isn't anything just let the pump sit in place


to name the things if I see them, that's what I call integrity..


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I needed to replace my radiator and the side effect was to let the engine run a little cooler. The fans still kick in at 110 degrees (as far as I can remember) but it takes much longer in slow traffic to reach the higher temperatures which improves the confidence that things are working as they should by a huge amount. I agree that radiators with rubbish stuck between the fins is more likely to be your problem than the thermostat.



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Simple solution.

Since you've got an SE I presume it has air-con? If so turn it on, that will kick the fans in automaticaly, regardless of the coolant temp. Then watch the gauge - it should stay in the 82'C range. If not, it's definitley not the thermostat - something more serious is happening.

Have you got an OBD-II scanner? That will read the coolant temp from the ECM's sensor - much more accurate than the gauge.

P.S. Did you get a re-cored radiator from SW Lotus at some point?

Edited by neal

May: DON'T hit it with a hammer!

Clarkson: Why?

May: Cause it's the tool of a pikey.

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It's the blocking of the radiator by road debris that's the problem. No amount of flushing will clear this, you need to get the car in the air and blow it clean from behind at the very least. A propper job would be to remove it but that opens up a whole new kettle of fish with sheared oil coolers etc....!

If your having issues do the above or risk an overheat! ££££££

Edited by Simon350S

Chunky Lover

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