Coolant Temp / Thermostat

The Oily Bits S2 Specific Topics
1

Hello folks. Now that my whiteboard is clear for another winter, time to start writing up the list for next winter.

My car has a ‘quirk’ where the coolant temp drops when I go full throttle. This may be normal for these cars, appreciate that usually you don’t get such a detailed readout of coolant temperature on a car dash but the digital readout on the Lotus stack can sometimes make you look for problems that don’t exist.

When the car was on the OEM radiator it did this but to a lesser degree, probably a 4-5 degree drop max. With the Pro Alloy rad I’m now seeing lower temperatures all round (cooler weather helping too!) and it’s potentially exaggerated the symptoms a bit. I’ll do some logging and make a graph (yay!) but for now the behaviour can be described as:

  • Coolant temp seems to settle around 82 degrees whilst ‘cruising’
  • A full throttle pull in any gear will drop it to low 70’s
  • A few moments later of ‘regular’ driving and it’s back up to 82.

The coolant system other than that works perfectly, heats up fine (so the thermostat is fundamentally working)

I’ve ruled out airlock purely because it happened both before and after my radiator change, seems unlikely that it’s been poorly bled twice and I’ve seen no other evidence of airlock symptoms like varying levels, hotspots, etc.

I did some forum searching, found responses varying from “TADTS” to electrical gremlins to failing thermostats. In my head the only logical thing I can think of is that the thermostat spring is a bit weak, the higher RPM is ramming the coolant past the thermostat and into the radiator circuit when it’s not required, resulting in a short burst of cold coolant coming in from the radiator. On a track session this probably normalises itself because eventually the coolant in the whole car is the same temperature and so premature opening of the thermostat is no longer relevant.

Even though a thermostat is a cheap part, it looks like a right ballache to get to so I’m in no hurry on this one - but thought I could gain some opinion of whether or not this is indeed normal or to be concerned about. I say that I’m in no hurry to sort it, but if we end up in lockdown perhaps it’s something to keep me busy… :lolno:

2

My car is around 87deg C.

If I really press on then the temps drop to maybe 82 and gently climb back to 87deg C.

Unless I am on track the happens all the time. It must be a slow reaction from the thermostat rather than a failure?

3

That sort of makes more sense, I’m 50% sure that the thermostat in our cars is 87 degrees - so your behaviour is probably a bit more normal. Mine doesn’t seem to get that high unless I’m:

a) revving it in the garage to bleed coolant
b) on track
c) driving in summer

If mine is getting to 82ish, then dropping down to 72ish - that’s what’s leaning me towards the thermostat being on the weak side? Could be talking utter twollocks though.

4

Low temp stat?

5

It certainly seems that way, but based on this cars’ past life I just cannot imagine anybody going out of their way to change the thermostat for a lower temp one, unless it was a mistake at the motorfactors etc.