2014 (204) C220 Estate

[Mcsterl]

Hi Folks,

I've got a concern on my C-class C220 Diesel, It takes an inordinate amount of time to reach operating temperature. typically my journey to work is A roads, and it currently takes around 20 minutes to reach 90 deg. The reaching of 90 coincides with the point in my journey where I reach a dual carriageway.

The fuel economy has taken a dent as a result, and has done so since early last summer.

I have had the Thermostat and coolant changed at the last service, which has made no difference. the whole unit was changed (including the sensor and electronic thermostat heater/controller). Genuine parts were used.

So I'm a little baffled, has anyone seen similar issues?

I've ordered a better OBD reader in the meantime.

Thanks, Paul.

 

[BMF]

A duff stat, from reading on this forum and t'other channel, it does happen, even with genuine parts

 

[Mcsterl]

Two in a row though? hmmm. You're right, it can happen, but the chances must surely be slim.

I will speak to the garage that fitted it yesterday.

I have also harboured thoughts that there could be an incorrect signal being sent to the Electronic stat control to open it early.

I've got the old stat at my desk, and we're going to do some flow tests.
Thanks, Paul.

 

[BMF]

Two in a row though? hmmm. You're right, it can happen, but the chances must surely be slim.

I will speak to the garage that fitted it yesterday.

I have also harboured thoughts that there could be an incorrect signal being sent to the Electronic stat control to open it early.

I've got the old stat at my desk, and we're going to do some flow tests.
Thanks, Paul.

Check that it is the correct temperature range too.

 

[DrNick]

Can you disconnect the electrical heater part and then see how long to takes to warm up? This would rule out early opening due to faulty control signal.

 

[Mcsterl]

Thanks DrNick, Yes we've thought about that too, so long as it doesn't cause a limp home, that should be possible. Right now a false signal to the heater is the most probable cause (though lord knows how that bit could be resolved).

 

[RedGull]

Mine takes longer than that to reach 90, ‘‘tis a diesel!!

 

[markjay]

Mine takes longer than that to reach 90, ‘‘tis a diesel!!

That can't be good news for the DPF....?

 

[Mcsterl]

Absolutely. Longer warmup has a severely negative impact on the DPF. the system protects it to a degree with regens, which further hits the fuel consumption, but ultimately will over tax the aftertreatment system.

And re diesels being cold to warm up, there is no reason why that should be the case over a petrol, if anything the opposite, as a diesel is far more prone to ailments caused by cold running than a petrol is (this Is partly why hybrids are almost all petrols, as they have less issues being used on-off like a range extender).

 

[Gazwould]

10 minutes or there abouts it should take , and in that time it'll be running rich .

I agree the dpf is a flawed system but this is why we buy .






Plus a good dollop of early torque .

 

[RedGull]

Yep need a new thurmost

 

[190]

Diesels are more thermally efficient than petrol engines and generally run at lower revs so that means less waste heat form combustion and less heat from frictional losses. Wouldn't that make longer warm up times for diesels inevitable.

 

[geraldrobins]

Mine used to take about 20 minutes to get to 90 if I remember correctly especially in the winter months so it seems normal to me.

 

[RedGull]

Been told by my indie should be around 10/12 mins, and as in that time running rich not very good for the DPF , mine does over 20 mins! So I assume really not good for the DPF !! Getting a new stat fitted.

 

[GeeJayW]

Diesels are more thermally efficient than petrol engines and generally run at lower revs so that means less waste heat form combustion and less heat from frictional losses. Wouldn't that make longer warm up times for diesels inevitable.

Yep, can be the case.

It's also worth mentioning that diesels don't run rich when cold. In fact unless the fuel mapping has been screwed up to get more power, they are smoke limited. Hence they always run lean (which is where the tailpipe NOx problem comes from).

If the exhaust aftertreatment systems are cooler than the light-off or regen temperature, then respectively the catalyst(s) won't work and the DPF regen can't happen.

The only reason to run a gasoline engine rich when cold is to have more volatile fractions available until the engine is warm enough for the whole charge to vaporise in the combustion space. Diesel doesn't have or need volatile fractions (which are unhelpful for compression ignion anyway).

As to the original question, long warm up times do point to a thermostat problem. That you've had a new one fitted and you still have a problem is a bit puzzling. The engine coolant should take no more than ten minutes or so to warm up. That said, the Ford Galaxy diesel we had years ago seemed to take forever in the winter. The Sharan that replaced it was better, but not by a lot.

 

[Mcsterl]

Yep, can be the case.

It's also worth mentioning that diesels don't run rich when cold. In fact unless the fuel mapping has been screwed up to get more power, they are smoke limited. Hence they always run lean (which is where the tailpipe NOx problem comes from).

If the exhaust aftertreatment systems are cooler than the light-off or regen temperature, then respectively the catalyst(s) won't work and the DPF regen can't happen.

The only reason to run a gasoline engine rich when cold is to have more volatile fractions available until the engine is warm enough for the whole charge to vaporise in the combustion space. Diesel doesn't have or need volatile fractions (which are unhelpful for compression ignition anyway).

As to the original question, long warm up times do point to a thermostat problem. That you've had a new one fitted and you still have a problem is a bit puzzling. The engine coolant should take no more than ten minutes or so to warm up. That said, the Ford Galaxy diesel we had years ago seemed to take forever in the winter. The Sharan that replaced it was better, but not by a lot.

Thank you for that excellent reply. I must admit, I did ponder pointing out that diesels run lean myself, but my answer would not have been nearly as thorough as yours.

My belief is that the issue on this C220 could be in relation to a trigger of the electronic thermostat heater, as the car warms up to 60 reasonably quickly, thus suggesting at that point that the wax stat is shut, but 60 to 80 takes an eternity, this morning in fact, the highest the car got is 75 deg. The coolant jacket of an engine is usually small in relation to the heat produced so that the stat is able to regulate the working engine to operating temperature even in pretty cold conditions.

In addition to this, I have leak checked the old stat on cold water, and there was no leakage, disproving there being an issue with it passing on cold. Even hot water (admittedly even water from the kettle doesn't stay near boiling for long) into the stat, there was no leakage.

To this end, the car is going back into Prestige to be plugged in to the computer to check what is going on with the Electronic stat control, the irritating thing is that should have been done before changing the stat, as I deliberately did not ask them to change it, I said "the car doesn't get up to operating temperature".

There is also the risk that the fan is on all the time as well, but even that wouldn't give all of the symptoms I am seeing, as it would at least reach stat opening temp before plummeting again.

Cheers, Paul.

 

[Mcsterl]

Hi Folks,
Had the car back to Prestige, and it was plugged into MB diagnostics tool. No fault-codes listed. They have suggested that 75-80 deg is the normal operating temp, and even so much as 41 mpg that I'd got on the journey to them was "pretty good" (it isn't, the car used to average at least 55mpg on my generally un-fuel efficient route to work, and high 60's on longer journeys).

I'm fairly sure the stat on this car opens at 92 deg, and that was its old operating temp, so I'm still of the opinion that the electronic stat heater is the issue (but probably not the root cause). So I've measured the resistance of the heater, about 10 ohms, and bought a suitable resistor to put across the heater plug so that it can be run detached from the stat housing, and will monitor the warm-up times from that. I believe the electronic stat heater is there as a heavy load/high temp buffer, so disabling it should be okay so long as ambient temp isn't overly high and duty cycle not excessive. Its only a one time test anyway.

Paul.

 

[garycat]

Mine takes at least 15 mins to get to temperature, even longer in the winter.

I'm not 100% sure about the OM651 but diesel engine blocks tend to be big iron lumps to handle the higher compression ratios so will take longer than say a 2.0L alloy petrol engine.

If it is DPF related, when I had my car at avontuning to get the DPF checked they said the pre DPF pressures were high and recommended this stuff, it seemed to help the car breathe more freely.

https://www.amazon.co.uk/dp/B0061ATRK2/?tag=amazon0e9db-21

 

[Mcsterl]

Yep The OM651 is an Iron engine, though this one used to (and most others I've dealt with in the flesh still do) take around 10 minutes to reach operating temp. My Toyota Surf actually reaches operating temp in around 5 mins, but that is incidentally a type of engine/cooling pack which is notorious for overheating/cracked heads.

Paul.