Erratic Engine Temperature

[Bo!]

Picked the car up from dealers today .
The master tech diagnosed with temp reading in mvbs, thermostat opening too early . Main stats been replaced under warranty 

[Mark_DF05]

Apologies for resurrecting an old thread but seems pointless creating another as I’m experiencing similar issues and think the thermostat could be at fault.

On my commute to work which starts off with 30mins of town driving including spots of heavy traffic and then 30mins of A roads I’ve noticed that the temperature fluctuates from 90°C to 80°C. The drop in temp seems to occur when I reach the A roads. I did a bit of reading on here and decided to monitor the coolant temp via the hidden menu as mentioned...

After about 16 mins (3 miles) the needle on the cluster had reached 90°C with the climate display showing 72°C which then increased to 80°C after around 25 mins.

Finally reached the bypass with free flowing traffic and as before the needle on the cluster dropped to 80°C  (68°C on the climate display). Hit some traffic at the end of the bypass and saw the temperature slowly rise back up to 90°C on the cluster (75°C on the climate display but imagine it would have gone higher the longer I stayed there.) Set off again and the temp continued to rise and fall dependent on traffic.

So in summary, when idling in traffic or slow moving round town the temperature reaches 90°C (82°C on the climate display was the highest reading) but can drop to 80°C (68°C lowest on climate display)

From reading up I think I can rule out the coolant temp sensor and this means the main thermostat is stuck open and needs replacing? This could also explain the poor fuel economy I’ve been getting recently.

Car is a DSG Edition 30, I’m aware that it has 2 other inline thermostats - am I correct in thinking that if one of those was faulty it'd take longer to get to temp as opposed to causing it to rise and fall?

[Juliand]

I haven't gone back over the posts here, but 10 degrees sounds to me to be within a reasonable variance, and down to traffic conditions - free flowing traffic allowing the radiator to do it's job, in cooling, and the thermostat/s kicking in and out with town traffic, and cooling fan doing the job to cool things off in town.......? lots of folk more knowledgeable than me though.

[Dan_FR]

Stat needs replacing. 68 Degrees C is 20-25 degrees lower than it should be. It should get to around 90-92 and vary maybe 5 degrees either side

[Mark_DF05]

That’s what I though, cheers. I’ll get it booked into the garage as it looks a pain of a job

[Mark_DF05]

Stat needs replacing. 68 Degrees C is 20-25 degrees lower than it should be. It should get to around 90-92 and vary maybe 5 degrees either side

Had the main thermostat replaced and picked the car up this morning. Drove to work, the needle reached 90° and stayed there so I think it’s solved the problem.

One thing though - the figures on the climate display are higher than they were before but never reached 90°. Highest was 87° and lowest was 83° whilst the needle stayed at 90°.

I’m guessing this is within tolerance and I should only be concerned if the needle actually drops?

[Shoduchi]

Stat needs replacing. 68 Degrees C is 20-25 degrees lower than it should be. It should get to around 90-92 and vary maybe 5 degrees either side

Had the main thermostat replaced and picked the car up this morning. Drove to work, the needle reached 90° and stayed there so I think it’s solved the problem.

One thing though - the figures on the climate display are higher than they were before but never reached 90°. Highest was 87° and lowest was 83° whilst the needle stayed at 90°.

I’m guessing this is within tolerance and I should only be concerned if the needle actually drops?

Yes.

[Mark_DF05]

Great, cheers for the reply