Could I have a dodgy thermostat?

[blondebier]

Hi all,

I've noticed something that might be nothing but I thought I'd post and see what other people's experiences are.

Our T6 coolant gauge takes a while to get up to 90'C. It's taking longer in the cold weather and that's to be expected.

What I've started noticing is that even after 10 miles it still might not be up to temperature. Some of my commute home is downhill and when I'm following something at 50mph it will often coast at very little above idle in D7.

Would you expect the coolant temperature to drop in this scenario? Mine does a bit.

If I use the steering wheel paddles and drop a few gears to get the engine revs up, the temp will increase.

Is the drop in temperature normal?

I'd half expect the coolant temperature to get 90'C after 10 miles and stay there. Even if the engine is just ticking over.

I'm also noticing it's a struggle to get the oil temp above 85'C even after 20 odd miles.

Perhaps I should turn the coasting feature off?

The only way I can get the oil hot is manual override with the paddles and hold the engine revs for a while. It's getting pretty tiresome when the speed limit is 50 and the DSG constantly wants me to be in D7!

Any thoughts?

 

[clarinetbcn]

Seems to be a characteristic of modern diesel motors which are very efficient and produce little heat as a waste by product. I do notice that If I start the van in winter above -5c in the mountains and go on a long downhill road the motor won't reach operating temperature. Fortunately I have the programable upgrade to the coolant heater, so I can turn it on manually and get the motor up to temperature in a few minutes, even if I'm coasting downhill. To be honest, I use it regularly to get the motor up to temp fast from cold starts anywhere, to minimize engine wear when cold. Below -5 the standard coolant heater should kick in automatically, but I agree that there is a grey area between very cold and warm weather where the engine can have difficulty reaching temperature depending on the driving conditions.

 

[Loz]

The thermostat should be actually holding it at 90 when it’s cold so if it’s getting jammed open then you may see the temperature drop.

I had this on a Land Rover discovery and the thermostat had given way and it was over cooling and the temperature was dropping the actual cause was a cracked cylinder head that was allowing diesel into the coolant and that are dissolved the rubber gasket in the thermostat. Unlikely to be the case of fuel in the Cali as the fuel doesn’t run through the cylinder head like it does on the discovery.

 

[blondebier]

Thanks Loz.

How would a dealer determine if the thermostat was faulty?

As it's under warranty would they just replace it?

 

[blondebier]

I thought I'd post a few more observations.

Having turned off "Coasting" it now holds the revs a little higher when in D7. I've noticed that on the same drive home (with long downhills), similar temp 6'C, the coolant temperature gets up to 90 after 7 miles. This is roughly 3 miles earlier than with "Coasting" enabled.

Driving in this morning it was -2'C, I'm assuming the webasto kicked in (although I didn't really notice), it still took 7 miles driving at 50MPH until the coolant temperature reached 90'C.

The oil temperature did get up to 101'C today after about 16 miles and then dropped to about 85'C as my speed reduced coming in to town after about 23 miles.

 

[Calibus]

Mine does the same, so does a friends, we both drive very laid back, I once managed to get from Leighton Buzzard to MK without it hitting 90, was at 3am mind you and I also got an average of 48mpg on that trip.

I’ve been berated for my advice on here before so I shall offer none and just say in my opinion I’m not worried about it.

 

[blondebier]

Mine does the same, so does a friends, we both drive very laid back, I once managed to get from Leighton Buzzard to MK without it hitting 90, was at 3am mind you and I also got an average of 48mpg on that trip.

I’ve been berated for my advice on here before so I shall offer none and just say in my opinion I’m not worried about it.

Thanks for your reply. It's good to hear that your experience is similar.

I wasn't overly worried, more interested in what other people's vans did in the real world.

I guess my main concern was that it wasn't getting up to operating temperature and was therefore inefficient.

Another good reason (if indeed you needed one) to get out and stretch its legs. These vehicles were made to be driven.

 

[clarinetbcn]

Thanks for your reply. It's good to hear that your experience is similar.

I wasn't overly worried, more interested in what other people's vans did in the real world.

I guess my main concern was that it wasn't getting up to operating temperature and was therefore inefficient.

Another good reason (if indeed you needed one) to get out and stretch its legs. These vehicles were made to be driven.

The internal parts of the motor will tend to wear more if it runs cold, since they won't have fully expanded to the operating dimensions they were designed for.

 

[MattBW]

Mine is exactly the same and has been from new.

• With the rear heater on, it takes even longer, I sometimes turn the rear to cold until its warm.
• If the temp is between about 6 and 8 it doesnt use the coolant heater but it is still quite cold, so is especially slow in those circumstances.
• If you have less than 1/4 tank the auxilliary heater won't come on.
• Turning up the rear heater can also cause a dip in the temp to below 90 as the cold fluid I assume mixes with the hot.

 

[blondebier]

Mine is exactly the same and has been from new.

Thanks MattBW. That's good to know.