Adverse effects of an overcooling engine?

[ben_r1]

Right on my daily runner, a mk1 1.4 Clio 1995, it's had a constant problem with it running very hot. I'm talking about it sitting right below the red zone on the gauge. Changed thermostat, radiator, fan switch, heater matrix and water pump all to no joy. Compression test come back fine and it doesn't lose any coolant.

So after running out of ideas I changed tactics, fitted a ktr low temp rad switch but still run red hot. Now the standard and replacement thermostat has 91 degrees stamped on it, quite high I thought, so I stuck a spare 197 thermostat in it at 75 degrees and bingo the car runs cool but it only ever gets to a quatre heat up the gauge.

Are there any adverse effects to an engines performance or lifespan by running it 16 degrees cooler? Fuel efficiency seems normal and the heaters are still red hot.

Thanks!

 

[Matt Cup]

It's not a dodgy dial miss reading is it?

 

[James23]

I would have thought it would use more fuel tbh. Your oil temperature will be lower now too I would have thought, which means that it may not evaporate any water off properly so you may get a bit of mayo on your filler cap etc.

But ^^ what Matt said, do you have a way of testing what the actual temp is?

 

[Steven103]

Sticking a 75 degree thermostat in does not neccessarily mean it will run 16 degrees cooler all the time, only that the thermostat opens 16 degrees earlier. Not to mention there is a good minute or so time delay between a thermostat being put in 71 degree fluid and a thermostat opening, by which time the fluid is well over 71 degrees. 91 degrees is fairly common (don't forget that the massive majority of systems self-pressurise thus, combined with anti freeze, raising the boiling temp of the water well beyond 100 degrees) widespread amongst Vauxhall/Saab/GM stuff.

If the engine is running too cold the ECU will use a particularly rich AFR designed to warm things (particularly the cat converter) up as quick as possible to get the cat working to minimise emissions. If you're constantly running too cold, the effect on MPG is usually very noticable (e.g. recently my not-a-clio was running too cold due to faulty thermostat & was getting 25/30 MPG instead of 35/40 even on motorways) You're also potentially not quite getting the oil up to temperature, though (complete speculation here) what's 16 degrees in coolant temperature to an engine block that experiences 500 degrees briefly everytime combustion occurs.

On the vast majority of cars you can check/log the actual coolant temp with an OBD2 tool connected to a laptop. Besides going "oh that's colder than I would've guessed" IMO this would be a little bit useless? There are several A4 pages of maths & lots of variables which no-one except Renault would know to get from coolant temp to something useful like oil temp.

 

[Dan519]

91 sounds high, and 75 sounds very low. I'd go somewhere in the middle, Try to get a stat in the low 80s