All Things Mk5 > How to Guides / Troubleshooting

Temp Gauge Fluctuating

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maxamplitude10:
Guys owned my Ed30 for 5 years and temp gauge has always been rock solid at 90deg TDC, however recently it has started dipping to around 70/ 80deg. Any ideas where to start and is this the initial signs of a head gasket going or simular?
I've bought a genuine temp sender unit but not convinced this is going to be the culprit, is it more likely to be a thermostat issue?
Any help would be massively appreciated:-)

Thanks in advance
MaxAmplitude

spinfaster:
I have a similar issue. For 4 years it's been a solid 90º. Last year it started reading more like 70º. At the same time I had a big loss of power which turned out to be the turbo over-boosting. It sorted it's self out, had the error cleared and it's never happened again, but the temp has since been reading odd. I had a new thermostat and sensor fitted but it's still reading 70º. If I leave the car running or drive fairly slow (~30mph) it'll reach 90º and sit there, but as soon as I'm moving over 40mph or so it drops again. I have no other issues. Let me know if you find out anything else!

muff1991:
Usually a thermostat or temp sensor, replace both if you have the money, if not, start with thermostat.


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maxamplitude10:
@spinfaster sounds like an identical issue to mine, do you find turning the heaters on and off makes any kind of influence?
I'm concerned it could be a head gasket issue have you noticed any loss in coolant?

 :thinking:

Cheers

f00glee:
Similar symptoms for me were cured by a thermostat, didn't touch the temperature sensors on mine as both seemed to be reading similarly and so presumably correctly. Which raises a point - there are two coolant sensors (at least on my '06 GTI) - one at the radiator and one at the engine block. Not sure which sends its value to the dash to be read out on they gauge, but its possible that you could replace the good one only to leave any potential fault with the other in place.

If you have VCDS its easy to read the live values of these in measuring blocks to verify their function. Just put the ignition on without starting the engine after its been sat for a few hours and if they both read the correct (and same) ambient temperature through VCDS then I'd guess the thermostat is the culprit. Mine was opening too soon (around 70C, should be 87C) so was fine round town but soon as it got any air through the radiator on the motor way it would hover around just under 90 indicated, which in reality was more like 70C as anything between 75C and 115C reads 90 on the gauge in the clocks.

"Real" coolant temperature can also be read out the the climate control display, again not sure if this is engine or radiator temperature though http://www.mk5golfgti.co.uk/forum/index.php?topic=50280.0

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