Remap & Engine temps (coolant)

[Drpaul10]

Hi all,
I've recently had my 2012 CLS 350cdi remapped (reputable company). Remap and rollback of the emissions alteration. 306bhp and just under 700nm (rolling roaded before and after). Following remap on drive home I noticed some strange goings on with my coolant temps. Usually my gauge would sit just under 80 when warmed up (this is how it's always been in the 6 years I've had it) and wouldn't move-very stable. What I've noticed is now the gauge is moving around a lot more. Seems to take longer to get to temps, then when it does if I go up hill it can go up to around 88degs or in traffic. I could also see it was doing a regen as coolant temp went up to about same level (idle was at 850rpm when stationary which is how I identified the regen). So initially I thought it was something to do with the remap as it just seems too much of a coincidence. However I'm more inclined to think now that it's the Thermostat that is on its way out.

Also I've seen people quote different running temps for the OM642 for the coolant. Some have said just under 80 some have said higher. Mine has always sat just under 80.

 

[MrGreedy]

I have pretty much the same engine. My engine is )M642 (642.852 to be exact).
Check your exact engine code to compare against mine.
I'm very certain it should be around 90°C, and 80°C sounds too low.
My car sits at 88°C all day long. I haven't thrashed it to death in hot weather, which is the only time I would expect it to increase above 88°C.
Once up to temp, I wouldn't expect it to ever fall below 88°C, regardless of normal UK outside temperatures.

Another forum member with the same engine on two family cars also sees 88°C
Coolant temperature on diesel | Engine

It's possible you have had a thermostat issue all this time, and isn't able to full close, hence struggling to get to 88°C unless the engine is worked.
Or maybe the temperature gauge you are looking at is faulty (although far less likely, given that it is moving within what sounds like the correct range).
Running at 80°C will affect efficiency and DPF operation/fill.

 

[Bellow]

It's possible you have had a thermostat issue all this time, and isn't able to full close, hence struggling to get to 88°C unless the engine is worked.
Or maybe the temperature gauge you are looking at is faulty (although far less likely, given that it is moving within what sounds like the correct range).
Running at 80°C will affect efficiency and DPF operation/fill.

Plus 1.

 

[Drpaul10]

Thanks. Maybe that's the case and it's always been dodgy then, maybe always just stuck half open or something. Mine is 652.853. I guessed that different engine models /ages had different set points related to emissions or natural evolution. Just rang local dealer to buy the OEM Part but they are going to have to order from Germany so Mercedes Newcastle have them on ebay. £154 Inc delivery so I've gone for that. It did worry me quite a lot when I saw the temperature swings especially seeing as I had just had the remap and you automatically put two and two together. Hopefully will be sorted after switching this out.

 

[MrGreedy]

For your reassurance, that price from MB Newcastle is reasonable. I haven't seen genuine any lower.
It's a relatively easy change I have read. I'm going to do mine at some point soon. You can get away with very little coolant loss and a top up, but given my car is 9 years old now, I will do a total drain down and refill with fresh coolant from Mercedes.

 

[Drpaul10]

From what I've read the OEM part is WAHLER (Borg Warner), this is what Mercedes Newcastle are supplying also when I zoomed in on the images. EuroCarParts have it on their website quite a lot cheaper but I'm not convinced they actually have any, they say its in store only and not for home delivery and no matter where I looked they carried no stock. I'm going to pick up a litre of coolant from Mercedes just in case but I saw a cunning trick with a chopped up 2L water bottle to minimise losses. According to handbook the coolant has 15 year life.

 

[E55BOF]

If you can raise the front of the car up - a 10% slope will do it - before doing any draining, all you need do is syphon out the expansion tank, and the thermostat housing will contain only air when you remove it.

Mine, too, is a 652.853. You will need to remove some of the turbo intake trunking, and I think detach the pipes from the fuel filter, to remove one of the three bolts that hold the thermostat housing in place.

 

[Bellow]

Once the new 'stat is in, keep an eye out for leaks. Running hotter the pressure in the system will be higher and may find a lazy seal hose or the likes. This effect will be at it most severe after a run where it's reached full temp and is now stopped and parked and the residual heat in the block etc bleeds into the (non circulating) coolant so easily checked on the driveway at home. Check the level and watch for puddles underneath the car for the next couple of weeks just as a precaution. I'm not saying this will happen - only that it could.

If you disturb any hose seals, do the final re-tightening with the system up to temp. Hoses are softer then and will tighten down a touch more for a better seal.

Changing the 'stat is definitely a good move. 80C is way too cold - and giving up combustion heat to the coolant at the expense of power and fuel efficiency.

 

[E55BOF]

No tightening needed - the hose just pushes into the thermostat housing stub, and is secured with a bent wire clip to stop it coming out. The seal is a built-in o-ring type.