Erratic Engine Temperature

[kahunajb]

I've noticed that my car temp gauge gets up to 90 degrees but doesn't necessarily stay there. It can drop down to around 75-80 degrees depending on how I am driving then go back up to 90 again. I presume this is not normal. Do you think the coolant temperature sensor needs replacing?

[bacillus]

What sort of driving are you doing when it drops down to 75-80C?

[Degudodger]

Sounds like the temperature sensor, should be a cheap fix.

[kahunajb]

What sort of driving are you doing when it drops down to 75-80C?

I think it may be when I am driving slower it drops but it might just be randomly.

[OSB]

I have the same issue.
 Engine coolant thermostat is my first thought. Or could it be the coolant temperature sensor.
Which is easier to change and therefore eliminate?

[Type_R]

Engine Coolant Temperature sensor is really easy to change, but get a genuine VW one - not a cheap eBay one (I made that mistake and thought the problem still existed, changed to a VW genuine one and all is well again).

Thermostat is ~£130 to change by an indy as you need to remove the alternator to get to it.

EDIT: Check out my thread on this topic http://www.mk5golfgti.co.uk/forum/index.php/topic,62567.0.html

[OSB]

Engine Coolant Temperature sensor is really easy to change, but get a genuine VW one - not a cheap eBay one (I made that mistake and thought the problem still existed, changed to a VW genuine one and all is well again).

Thermostat is ~£130 to change by an indy as you need to remove the alternator to get to it.

EDIT: Check out my thread on this topic http://www.mk5golfgti.co.uk/forum/index.php/topic,62567.0.html

Many thanks. Will get a VW sensor next time I'm passing.
£130 for changing the thermostat!!!! No wonder the stealer where I bought the car was not keen on changing it!

[kahunajb]

Finally got round to changing my coolant temperature sensor however I am still having the same issue. Today when on the motorway cruising gauge was at a steady 90 however when I got to a long downhill section and engine was under less load it dropped down to 75-80 ish and once stopped in traffic went back up to 90.

Does this sound like it could be the thermostat instead?

[Nafeun]

Thermostat stuck half open by sounds of things so yeah.

[sandancer]

Mine does the same, I wouldn't worry about it as most cars will tend to do this depending on ambient temperature, driving style, flat or hilly countryside etc.
As long as the car warms up withina few miles and the needle sits and returns to 90 deg. it's perfectly normal.
What's your mpg by the way ?
25-28 urban driving and 32-35 A road/motorway cruising is perfectly normal, if you're getting significantly less than this then you may well have a problem, otherwise enjoy the car !

[JPK]

I had the exact same problem, replaced the coolant temp sensor and it didn't do much. Just had the thermostat changed and the problem is finally sorted. Gets to 90 degrees nice and quickly and also feels a fair bit quicker as it isn't running rich trying to get to temperature the whole time.

[OSB]

Glad to hear it solved the problem. Have the same issue - If you don't mind saying, how much did you pay to have the thermostat changed?
I need to get mine done and just don't have the time to do it myself.
Thanks

[Bo!]

Kahunajb did you get to the bottom of this I'm having same symptoms as you were .

[Shoduchi]

Kahunajb did you get to the bottom of this I'm having same symptoms as you were .

Erratic readings, not dependent on engine charge, it's the temp sensor. Low readings when driving slow or downhill and normal when stopped in traffic, most likely one of the engine stats.

[Bo!]

My temp gauge is dropping from 90 under engine breaking when leaving the motorway coming off a slip road drops to around 80 . I've booked it in to be done while Im still under warranty but worried it's not bad enough .