3.5 petrol M272 not getting up to temp

[clk208]

Hi folks.

Noticed of late that my CLS which has the 3.5 petrol engine isn’t quite getting up to temp according to the coolant temperature display, even after 30-40miles. Display seems to indicate a temp of 60-70 when I believe it should be closer to 90.

I was thinking maybe the thermostat has gone lazy but read this about my engine from this very forum:

New electronic coolant flow control has replaced the mechanical thermostat for improved engine warm-up and optimum control of engine temperature.

Any thoughts?

 

[DrNick]

Sounds like a slam dunk thermostat issue.
Looks like yours is relatively straightforward
https://www.billsden.org/fileadmin/media/mercedes/slk/docs/train_engine_m272.pdf about slide 57 shows that your thermostat may be relatively straightforward but has electrical assistance. Not sure about the rest of the cooling system see page 56/57

Be warned though that when I had a cooling issue on my E250 I had to do a lot of digging to work out what was going on due to a complicated cooling system.
E250 temperature gauge issue?
In my case, although it was presenting as a thermostat issue, in turned out to be an overly complicated water pump. A Russian youtube video explained the fault and the cure, but it took a lot of finding! Hopefully yours is straightforward but the link I gave for your engine only describes the thermostat, not the whole cooling system. It might be prudent to do some more digging if the thermostat is expensive.

 

[Uky]

Easy to replace yourself unless there is an extra air injector pump in the way (some versions of M272)
that needs to be removed. Takes about one hour. You will need some new coolant (MB Approved...) too
and then maintain a careful check that any air bubbles leave the system in a proper way after replacing the
thermostat. Also bring an extra bottle of coolant and drive slowly while stopping every now and then to "top up".

 

[anderoo]

Mine did exactly the same thing and eventually the CEL lit up and it threw a code. Just needed a new thermostat.

 

[moosehead]

Same thing with my M272 2.5L. Took ages to warm up and after a few days the engine management light came on. Indie put it on star and it came up with thermostat fault immediately.

 

[Salal]

If its not getting to temperature the most common issue is definetly the thermostat, in this case stuck slightly open so you'll experience longer warming up times and failure to reach operating temp as you've mentioned. Although it could be the coolant temperature sensor not reading properly which you could easily check but that is less likely. You'll probally would have noticed your MPG suffers quite a bit as well. Always good idea to get a replacement from MB as some aftermarket have different opening temperatures. Last time I bought one from MB was about £50 from what I can remember, so not much more than most aftermarket ones. But BEHR are the suppliers to MB if you want to get one from elsewhere which would be more or less the same.

 

[BaldGuy]

Defo Thermo...did mine last year....

 

[clk208]

Thanks chaps. Will order the part from MB as most of the usual sources only seem to have cheap brand items.

Then some YouTubing to see if I fancy having a go otherwise will get it booked in hopefully while I wait.

Yes be interesting to see if the fuel economy picks up after change.

 

[Salal]

You might as well change the coolant if it’s not been done recently, since you have to drain most of it out regardless. It’s worth getting that from MB too as it’s hard to source a decent compatible one with the same qualities that last as long for a cheaper price. They come in 1.5L bottles in concentrated version.