Erratic Engine Temperature

[Dan_FR]

It should not deviate from 90 on the dash at all once it has reached operating temperature. The 90 on the dash covers a huge temperature range from 75 degrees up to over 100.

Once mine hits 90 on the dash it stays there, no matter what. The true coolant temperature reading can fluctuate between high 80's up to around 94 or 95 which is perfectly normal, but the gauge will stay solidly on the 90 the whole time

[Bo!]

The gauge definitely dips after it has been up to 90 its happening under engine breaking. I Used secret clima control setting 19.2 on a steady run it sits around 72-76,When I got stuck in traffic it went up to 87 on the digital clock. Because it doesn't dip down loads of 90 on the dash I'm concerned the dealer may say it's nothing to worry about il have to wait and see it's going in tomorrow, I think it's down on power a little aswell because of this .

[Madone]

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 !

This is def not perfectly normal and no engine should do it !, the thermostat opens and closes to regulate the temp in the engine. The rad temp will fluctuate but the engine itself will be constantly regulated by the stat. The issue is with the stat, it's not opening and closing as it should.

[Bo!]

I will post up the outcome tomorrow after I have been to the dealership. It has only recently started doing this in say the last month I only drive the car on weekend, and things like this tend to go unnoticed when the missis only drives 5 mile to work and back each day. I just have a feeling that the dealer may not support me on a warranty claim .

[stuart-88]

I have the same issue. Very rarely does mine get up to 90 and actually stay there for long, usually sitting around the 80 mark or thereabouts. Tempted to get a new temp sensor and see what happens.

[Dan_FR]

It will more than likely be the thermostat causing it mate

[Shoduchi]

It will more than likely be the thermostat causing it mate

What Dan_FR said.

[pudding]

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.

One of?! Blimey. 

Pretty sure mine need doing.  MPG is woeful and the performance is shat off boost.  Time to get my hands dirty!

[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.

One of?! Blimey. 

Pretty sure mine need doing.  MPG is woeful and the performance is shat off boost.  Time to get my hands dirty!

Engines with manual gearbox have 2 stats. Engines with DSG pre-2008 (or 2007, I'm not sure) have 3 stats and from 2008 (or 2007) have 2.

Mine has 2 stats and the DSG stat was malfunctioning. I had the 2 stats and 3 temp sensors replaced during the mechanical overall.

[Bo!]

 
Went out with a master tech today drove up hill and engine temp on dash dial was up to 90 and stayed there ,coming downhill I asked the tech to engine break and after a short space of engine breaking pretty much straight away temp started to drop off the tech continued engine breaking & got the temp as low as 70 on the dial. He agreed it's not right but was a little confused as to why this was happening under engine breaking as a thermostat will usually show symptoms of failing under load . Its booked back in next week a thermostat and temp sensor is on order so they have the parts if needed .
Just hope it gets sorted .

[Madone]

The irony is that by the time he gauge in the car shows an issue it's likely been happening for a long time. The gauge will read 90 at any temp from around 77deg and up to over 100. I never saw the gauge move in my car but checked the temps with vcds and saw the temps fluctuating. But the gauge not moving. Mpg wasn't good either as the engine wasn't getting hot. Surprised the master tech relies on the gauge !   

[pudding]

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.

One of?! Blimey. 

Pretty sure mine need doing.  MPG is woeful and the performance is shat off boost.  Time to get my hands dirty!

Engines with manual gearbox have 2 stats. Engines with DSG pre-2008 (or 2007, I'm not sure) have 3 stats and from 2008 (or 2007) have 2.

Mine has 2 stats and the DSG stat was malfunctioning. I had the 2 stats and 3 temp sensors replaced during the mechanical overall.

Cheers mate.  I'll get the bits in and save that job for when I do a manual decoke. The main stat on the engine block looks far more accessible with the intake out of the equation!  Where is the other stat? Mine's a manual.  Cheers.

[Bo!]

The irony is that by the time he gauge in the car shows an issue it's likely been happening for a long time. The gauge will read 90 at any temp from around 77deg and up to over 100. I never saw the gauge move in my car but checked the temps with vcds and saw the temps fluctuating. But the gauge not moving. Mpg wasn't good either as the engine wasn't getting hot. Surprised the master tech relies on the gauge !   

The master tech did say they can read the engine temp with their computer probably the next step when it's in next week before any things replaced .just hope it gets sorted and its not something else ,seems strange that the temp only drops under engine breaking .not sure how long it's been happening but hopefully will get sorted .

[Dan_FR]

Thermostats can fail in a variety of ways, yours is stuck open or not fully closing. If it was the other way round then the symptoms would show up under load and the car would overheat.

[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.

One of?! Blimey. 

Pretty sure mine need doing.  MPG is woeful and the performance is shat off boost.  Time to get my hands dirty!

Engines with manual gearbox have 2 stats. Engines with DSG pre-2008 (or 2007, I'm not sure) have 3 stats and from 2008 (or 2007) have 2.

Mine has 2 stats and the DSG stat was malfunctioning. I had the 2 stats and 3 temp sensors replaced during the mechanical overall.

Cheers mate.  I'll get the bits in and save that job for when I do a manual decoke. The main stat on the engine block looks far more accessible with the intake out of the equation!  Where is the other stat? Mine's a manual.  Cheers.

I guess I was induced in error by this topic: http://www.mk5golfgti.co.uk/forum/index.php/topic,78341.0.html.

Yours only has one. DIY: http://www.mk5golfgti.co.uk/forum/index.php?topic=93576.0.