I think my Thermostat is stuck Open!

[Type_R]

Well after my other thread changing the Engine Coolant Temp Sensor, my problem temporarily got better now seems to have got a lot worse.

Basically I used my VCDS to measure blocks 130/131/132/134 to monitor engine and coolant temps whilst driving over about 30 miles on the motorway.

My gauge never went above 80C. VCDS reported an engine coolant temp of a MAX of 68C and a radiator leaving temp of 48C. I have also been averaging about 5-6 mpg less than I normally do. The radiator fans never come on, probably because the engine is always way too cold.

Oddly I think block 137 showed an engine coolant temp of -48C and just stayed there throughout.

This all sounds to me like my thermostat is stuck open? Anything else I can do in VCDS to confirm this? It cannot be good for the engine to be running at 67C over a 100 mile drive down the M40!

So the question is how easy is it to replace the thermostat and whether I should try and do it myself or get VW to do it? It was an Indy who did it about 1.5 years ago and here we are again.

[Type_R]

So I decided to do quite a lot of VCDS logging today and it all seems a little weird.

Basically the car is specifying an output radiator temp of 90C but it only ever seems to get as high as mid 70C which means that the engine output coolant temp is around 70C also. However when the engine starts to get warm the radiator definitely opens and cools the engine back down to high 60C/ Low 70C.

So the thermostat is definitely working, just seems to be opening too early and bringing the coolant engine temps down to low/mid 70C which is below the 80C specified as a minimum.

I wonder if the Indy fitted an incorrect thermostat that opens too early? On VCDS you can log the engine coolant temp and the radiator output temps as well and they vary from 0 - 21C so the radiator is definitely opening and closing depending on the position of the thermostat.

I am going to change my Engine Coolant Temp Sensor again (for a VW one) to see if its just an error of temp reading.

[TANNER]

Hi mate, just for ££ reference my car is reading a max of about 60degrees when warmed up at the mo, was at Midland VW Saturday and they quoted approx £130 to replace the thermostat.
I haven't noticed any dip in mpg yet but sure i would over some distance.

[Type_R]

Hi mate, just for ££ reference my car is reading a max of about 60degrees when warmed up at the mo, was at Midland VW Saturday and they quoted approx £130 to replace the thermostat.
I haven't noticed any dip in mpg yet but sure i would over some distance.

Thanks for the info. Let me know how you get on with that.

I have noticed that my car warms up quite quickly (the interior I mean) which goes against there being a problem with the thermostat. Having said that even on Hi I don't really get hot hot air blowing in.