2022 model year GLB - very slow to warm up?

[Digsy]

Another question about my new GLB.

About a fortnight after collecitng the car I noticed that it was warming up very slowly. It takes a full seven miles of A and B road driving at speeds up to 70mph for the car to reach the normal operating temperature of 90 degrees. If during that time I have to slow down or wait at a junction, the coolant temperate actually starts to drop again very fast. It is very easy to see on the temperature gauge. Once it eventually reaches 90 degrees, it stays there and the gauge doesn’t move any more until I key off. This looked to me like the thermostat or cooling control valve was stuck partially open and coolant is flowing through the radiator all the time, hence the slow warm up and tendency to cool down again while driving slowly or at a halt. However the car has been in at MB today for this and some other issues and I was just told that "they all do that, Sir".

I'm not convinced. I would expect a modern car to reach running temperature within a few minutes to lower friction and reduce emissions. There should be no cooling going on at all until the thermostat starts to crack (I wish I had felt the top hose on a cold start before the car went in now). Also the courtesy car I was loaned (A200) warms up in just 4 miles. Yeah, different car, different engine, but that's much more like the time / distance I would expect to see. Interestingly though, the temp gauge in that car also goes up and down during the warm up phase.

My C-class never did this. I believe that the 8DCT in the new A and B classes use electric valves to manage engine and gearbox cooling so maybe I am just too "old skool", but it still feels wrong to me.

Can any other diesel GLB owners comment on how long their's take to reach normal operating temp?

 

[onefortheroad]

Another question about my new GLB.

About a fortnight after collecitng the car I noticed that it was warming up very slowly. It takes a full seven miles of A and B road driving at speeds up to 70mph for the car to reach the normal operating temperature of 90 degrees. If during that time I have to slow down or wait at a junction, the coolant temperate actually starts to drop again very fast. It is very easy to see on the temperature gauge. Once it eventually reaches 90 degrees, it stays there and the gauge doesn’t move any more until I key off. This looked to me like the thermostat or cooling control valve was stuck partially open and coolant is flowing through the radiator all the time, hence the slow warm up and tendency to cool down again while driving slowly or at a halt. However the car has been in at MB today for this and some other issues and I was just told that "they all do that, Sir".

I'm not convinced. I would expect a modern car to reach running temperature within a few minutes to lower friction and reduce emissions. There should be no cooling going on at all until the thermostat starts to crack (I wish I had felt the top hose on a cold start before the car went in now). Also the courtesy car I was loaned (A200) warms up in just 4 miles. Yeah, different car, different engine, but that's much more like the time / distance I would expect to see. Interestingly though, the temp gauge in that car also goes up and down during the warm up phase.

My C-class never did this. I believe that the 8DCT in the new A and B classes use electric valves to manage engine and gearbox cooling so maybe I am just too "old skool", but it still feels wrong to me.

Can any other diesel GLB owners comment on how long their's take to reach normal operating temp?

My e350 would take longer than 7 miles to get to 90 . Still does tbh. Diesels tend to heat up quickly if driven hard.

 

[AndySlade]

As above, diesels can take ages to get up to full temperature, especially in cold weather. The other cause could be a thermostat that is leaking and falling open or partially open, it’s quite a common fault on the 220 diesel engine. I”d say for the cost it would be worth replacing the thermostat, with it’s housing and a new temperature sensor and housing to block gasket.

 

[Blobcat]

As above, diesels can take ages to get up to full temperature, especially in cold weather. The other cause could be a thermostat that is leaking and falling open or partially open, it’s quite a common fault on the 220 diesel engine. I”d say for the cost it would be worth replacing the thermostat, with it’s housing and a new temperature sensor and housing to block gasket.

Problem is that new thermostats are a £££ cost as they have electronics and not just a ball of wax anymore

 

[onefortheroad]

If your temp drops whilst standing then you have an issue , if anything it should creep up , unless you've got the blowers on with heat on full. As above it's maybe time for a replacement thermostat.

I took a drive today and it took about 8 miles to reach near 90.

Just noticed yours is a 22 reg.

 

[fabes]

Would this not be a warranty claim on a car under a year old?

 

[malcolm E53 AMG]

What’s the fuel consumption if the stat is partially sticking open you will notice a drop-off in mpg. If the car is ok in this respect (you need to make an allowance for cold weather) and the heater blower is providing cabin heat in a reasonable time there can’t be much wrong.

 

[Digsy]

Thanks for the replies. I must say I am surprised that everyone is reporting back similar distances to get their cars up to normal temperature. I am sure my C-class warmed up faster but only because I never noticed this as an issue before as opposed to actually measuring it.

Yeah, the car is brand new, so it would be a warranty issue if I could get MB to accept there is a fault, which right now, I cannot.

The fuel consumption is 44mpg on the dash and 42mpg calculated by myself. It's about on the nose of where I expected it to be based on a test drive in another GLB before I bought it.

So it remains that the oddest thing here is that until it gets up to temperature, the gauge can go down as well as up. Maybe as suggested by Blobcat this is because it's not as simple as a wax stat anymore. I don't know what cooling system controls the 2.0 diesel uses but I know that in other applications the 8DCT uses an electronic valve for cooling. And as I said, the A200 I have on loan does exactly the same thing, albeit while warming up faster. Again, the MB guys told me that this was totally normal behaviour.

I will get the car back and check the top hose temp during warm up at the weekend. If it gets warm before the coolant gauge is showing much below 80 then I will know the stat is stuck open.

Does anyone know the thermostat opening temperature for my engine? Its a 200D

 

[Rory]

I know it's a different car but my wife's 2 litre diesel Tiguan is interesting in that it can display the engine oil temp. It's well into the teens of miles of rolling driving before it's at 90C.

In her car, and I wouldn't be surprised if all modern cars are like this, the water temp gauge doesn't display the actual water temp at all. It displays an output from the engine ECU - it goes up pretty quickly (the car apparently has multiple micro cooling circuits) and then sits solidly at 90C no matter what happens. It's basically just saying "OK". The oil temp, on the other hand, varies quite a bit depending on engine load, speed etc.

It's possible there's something wrong with your car though. For instance, on VWs with DSG gearboxes, the gearbox thermostat can stick open and cause very long warm up times. Maybe Mercedes does something similar.