GTI Engine Temperature Gauge Fluctuation

[ChrisPeers]

I've just taken ownership of a 90,000 mile GTI. It's got FSH and receipts for all work and is in good condition and completely standard so I believe I got a good one.

I drove it back from Yorkshire today and on the ride home I noticed that the engine temperature gauge fluctuated continually between 70 and 90 degrees which left me slightly concerned.

When I slowed down to say 50 or 60mph the gauge dropped to 70 degrees but when I kept the engine at 80mph or above it went back up and sat just under 90 degrees as though it was normal.

At idle the gauge sits at a fraction under 90 degrees. Which seems normal but I've never owned a car where that gauge moved unless there was a problem.

Should I be worried or is this common?

Any help appreciated.

Thanks


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[peter_booker2003]

Sounds like the thermostat to me. Common problem as they get stuck open. Worth getting sorted as you will find mpg will be down as a result. Looking at £200 ish fitted at a local indy.

[Deegti]

It's the thermostat alright,I just replaced mine last weekend as I was having the same symptoms as you,30 quid from eBay for a genuine part and 3 hours labour with plenty of swearing and bloody hands lol.

[lukemk5gti]

Is it manual or DSG?

They both have a main thermostat and an inline thermostat.
DSG has one additional inline thermostat.

Main:
This is a pig of a job and unless you're very capable you will need a garage to do it.
Issue is that the engine never reaches 90 unless in traffic, drops to 60 or so while cruising.

Inline:
Not too bad to change.
Issue is that it takes the engine often up to an hour to get to 90. It should take 4 mins or 2 miles give or take.

My build thread shows my inline being replaced - http://www.mk5golfgti.co.uk/forum/index.php/topic,89715.msg907250.html#msg907250

[ChrisPeers]

Thanks. I've got the DSG version. I'm definitely not capable of doing the work myself. Garage it is.


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[slix]

Does anyone know if a bad thermostat would cause a loss in performance?

Only asking as there was a mk5 on a dyno once and it was 20bhp down on power as the car wasn't up to temp yet. When it was up to temp it pulled bang on figures.

[lukemk5gti]

Does anyone know if a bad thermostat would cause a loss in performance?

Only asking as there was a mk5 on a dyno once and it was 20bhp down on power as the car wasn't up to temp yet. When it was up to temp it pulled bang on figures.

The ECU limits power on low temperature to protect the engine.

As to what level of restriction I cannot say.

20bhp would have been a good guess.