Lazy thermostat - keep an eye on yours!

[ajuniper]

Add another ST170 with identical (cold) behaviour.

My trip to work is 13 miles mostly on free flowing 50mph limit A roads. When the ambient temperature was around 0, the engine temperature was barely on the gauge after ~25 minutes driving.

I've also noticed on days when the ambient temp is less than 6-7 degrees that it struggles to warm up and will also cool down by 10-20 degrees when the speeds slow - which I thought that the thermostat was supposed to control.

I've long believed that this isn't right and also that the garage would fob me off if I tried asking about a warranty replacement but armed with this thread I think that I'll give it a try...

 

[Legohead]

Karl, could you give us an update when we get colder ambient temperatures please? I'd like to see a more comparable check with outside temps closer to zero.
I think we would have good evidence to push for new stats at the dealers then

 

[M7R]

Yep of cause I can, it might not fully cure the issue as it appears the in car heater is very efficent at removing heat if you whack the temp up, however I am sure mine is at least warming up a bit faster,

 

[Loonyjuice]

Yep, I have seen the same 'issue' where the temp takes ages to get to 90 and then randomly drops back to 70.

It's to do with the 'stat being closed to allow the engine to warm quicker - a smaller mount of water in the engine. When it eventually gets warm, it opens to allow the rest of the still cold water into the loop and that's what causes it to drop back down. Combine this with the heater on full and you can drag it back down to 50.

It's nothing to worry about.

 

[Loonyjuice]

FWIW, here's a technical bulletin from a friend of mine, who works for Audi Blackburn.

Technical product information Transaction No.: 2020133/12
Engine temperature display fluctuates between 50° and 90° C - all TDI Release date: 04-Dec-2012
Customer statement / workshop findings
At outside temperatures under 5°C the engine temperature fluctuates according to the display in the dash insert between 50 and 70°C or till the coolant temperature reaches 90°C. The phenomenon occurs mainly when driving at low engine speed.
Technical background
Because of a very good effectiveness of the engine in low rev range, little engine heat is passed on to the coolant. At low outside temperatures the coolant temperature does not reach 90°C. If the heating is used, the coolant loses further heat depending on the blower level. As a result, the coolant temperature can fluctuate between 50°and 90°C.

Below an outside temperature of 5°C and a coolant temperature of 70°C the standard PTC auxiliary heater is activated, to heat the interior. The best effectiveness of the PTC auxiliary heater is achieved when the temperature is on 22°C and the air conditioning on "auto".
Production change
---
Measure
Please do not repair, this is normal. Warranty accounting is not permitted, warranty claims will be redebited!
Warranty accounting instructions
---
Parts information
---
Customer information

A low coolant temperature has no effect on the service life of the engine. An engine oil with suitable viscosity is used.

 

[ajuniper]

It's to do with the 'stat being closed to allow the engine to warm quicker - a smaller mount of water in the engine. When it eventually gets warm, it opens to allow the rest of the still cold water into the loop and that's what causes it to drop back down. Combine this with the heater on full and you can drag it back down to 50.

It's nothing to worry about.

I agree that that is normal behaviour, but under those circumstances I'd expect the engine then to come back up to thermostat temperature, not linger around the 50 degrees mark?

 

[DWaldie]

FWIW, here's a technical bulletin from a friend of mine, who works for Audi Blackburn.

Technical product information Transaction No.: 2020133/12
Engine temperature display fluctuates between 50° and 90° C - all TDI Release date: 04-Dec-2012
Customer statement / workshop findings
At outside temperatures under 5°C the engine temperature fluctuates according to the display in the dash insert between 50 and 70°C or till the coolant temperature reaches 90°C. The phenomenon occurs mainly when driving at low engine speed.
Technical background
Because of a very good effectiveness of the engine in low rev range, little engine heat is passed on to the coolant. At low outside temperatures the coolant temperature does not reach 90°C. If the heating is used, the coolant loses further heat depending on the blower level. As a result, the coolant temperature can fluctuate between 50°and 90°C.

Below an outside temperature of 5°C and a coolant temperature of 70°C the standard PTC auxiliary heater is activated, to heat the interior. The best effectiveness of the PTC auxiliary heater is achieved when the temperature is on 22°C and the air conditioning on "auto".
Production change
---
Measure
Please do not repair, this is normal. Warranty accounting is not permitted, warranty claims will be redebited!
Warranty accounting instructions
---
Parts information
---
Customer information

A low coolant temperature has no effect on the service life of the engine. An engine oil with suitable viscosity is used.

That's reassurance enough for me. Anyone got info on the PTC Aux heater?

 

[M7R]

Today was the first proper cold day with a long run to check the stat, and so far it's looking better...

1deg outside and a run from Nottingham to just outside stoke in Trent on the a50 dual carriage way.

Temp was up quicker than before, and even with the temp in the car set to a toasty 26deg once it was upto 90 eng temp it stayed there no matter if I was sat doing 50 60 or 70 ... Tried all 3 at a steady pace tickling the throttle for 5 or so miles each, no change in temp... It did cool off a little when I coasted in gear 1/2 a mile to the island and sat waiting for a min but it soon came back up. Dropped the heater temp to a more normal 21 deg and all was well..

When I did the last 10 miles on the country road sat behind a lorry doing 40 in 6th so engine at about 1100rpm the temp did fall off a bit but it soon came back up after any acceleration.

On the whole I do believe it is better! Before when it got to about 1deg outside the car would run cool on the motorway! Now it seems pretty solid so I would suggest others get their dealers to do the same and see how they get on,
Karl

 

[ajuniper]

A couple of weeks back Seat in Aylesbury replaced the thermostat (and housing for some reason) on my car, under warranty.

Whilst the engine still doesn't really warm up when it's cold, the temperature does seem more controlled and the heater does seem warmer.