Overheating (sort of)

[maltbbe]

I have a tuned mk5 GTI with a k04 and supporting mods (s3 injectors, big HPFP etc). It’s been dead reliable until now. I took it to the track the other weekend and ever since it’s been running about 10 degrees C hotter than normal — between 98-102 degrees in normal driving.

The actual temp gauge on the dash hasn’t moved from the middle, but I have an aftermarket gauge (a Kufatec module that reads data straight from the ecu) that’s giving me the higher numbers, and have been driving with VCDS on a laptop in the passenger seat.

To be clear I don’t think the car is dangerously overheating at 102 degrees — it’s just that it’s never run that hot before (usually sits between 88 and 93 degrees), and it seems wrong for it to be running above 100 degrees after 10 minutes of calm driving. I haven’t driven it much, or for more than 10-20 kms at a time, since it started doing this a few weeks back.

No error codes or faults in VCDS. It’s running and idling totally smooth, and not down on power or anything.

Before I go tearing in to the cooling system or send it off for a new water pump — is there anything I’m missing?

[Lucas_R]

Could be a faulty coolant temperature sensor or perhaps a thermostat that is stuck partially closed?

[maltbbe]

I wondered about thermostat. The oil temp is also running higher than normal so I think the coolant temp sensor is OK. I guess my big concern is if it’s the water pump, cos it would mean doing the whole timing belt job. No idea if this would be a normal symptom of a failing water pump in these cars though.

[Suncoaster]

Hi, If it was the water pump I would expect some other symptoms such as an additional or strange noise, or perhaps some leakage with coolant levels declining.Not impossible , but the thermostat is a good starting point as it's not expensive in the scheme of things.Don't rule out a radiator blockage which you could address at the same time that you attended to the thermostat. Also, as this started after you tracking the car, perhaps there is an issue with the EGR system. I have had overheating problems in an old Toyota years ago with a faulty EGR system. Cheers-John

[maltbbe]

Thanks all. New thermostat and rad are both in the post — will report back.

[maltbbe]

Update: replaced the thermostat and put in a new aftermarket rad, and I think it’s helped — temp now seems to stay steady between 92-94 degrees in regular driving. Not as low as I’d like but it’s better than it was. I think it was the thermostat — the old one doesn’t seem to open if I put it in boiling water. Could have been a much worse outcome without an aftermarket temp gauge!