W212 Petrol Coolant Temp Fluctuations

[cheapshots]

Hi all,

W212 Petrol, M274 Engine, 2013, 60k mileage

Coolant temp in town is stable at just under 90 which is fine........when travelling high speeds it's mostly at 80, however it will dip to 60's if I'm coasting.

Had a MB software update recently (for the gearbox) but apart from that, the car has been fine.

Is this temp fluctuation normal?

 

[EmilysDad]

I'd suggest the thermostat needs replacing ... the car is over cooling ie thermostat is still open when it should be starting to close.

 

[cheapshots]

If the thermostat is playing up I wonder why in-town the temp is normal and stable at 90...

It's almost as though the car is intentionally dropping the temp to 80 when driving at high speeds....

 

[EmilysDad]

If the thermostat is playing up I wonder why in-town the temp is normal and stable at 90...

It's almost as though the car is intentionally dropping the temp to 80 when driving at high speeds....

because the thermostat is closing enough ie a little bit to cope with the minimum air flow over the rad at town speed. At high speed, the thermostat can't shut down enough to cope with the higher air flow over the rad.

 

[grayb]

Our car was the same (even though it's a different engine). New thermostat cured it - now 90 solid everywhere.

 

[LostKiwi]

It's all to do with air flow through the radiator. At low speed there is very little air flow over the radiator. On motorways there is loads of air flow.
Therefore round town and in traffic temperature will increase and on a motorway the engine will cool down.
Heat and cooling cycles are a bad thing for engines so thermostats are fitted to even the temperature out.
Your symptoms are classic bad thermostat.
I'd imagine it takes a fair while for the engine to warm up too.

 

[cheapshots]

Thanks all. It sounds like it is the thermostat. For arguments sake I bled the coolant system, topped up a little and will test the car tomorrow. If it's still playing up then I guess it's off to the garage, unless it's a DIY job?!

Can't find a thermostat on Euro Car Parts. Guess will have to call MB... Will keep you posted about how I get on tomorrow.

 

[cheapshots]

Hi guys, having bled the coolant system, the issue persists. New thermostat it is - anybody managed to change it themselves? Below is a link to the part I think I need (will confirm this with MB this morning).

NEW Genuine Mercedes-Benz OM274 Petrol Engine Cooling Thermostat A2742003300 | eBay

Suitable For Selected OM274 Petrol Engines. Unsure on Suitability?. Useful Links. Can’t find what you're looking for?.

www.ebay.co.uk

 

[Blobcat]

It's all to do with air flow through the radiator. At low speed there is very little air flow over the radiator. On motorways there is loads of air flow.
Therefore round town and in traffic temperature will increase and on a motorway the engine will cool down.
Heat and cooling cycles are a bad thing for engines so thermostats are fitted to even the temperature out.
Your symptoms are classic bad thermostat.
I'd imagine it takes a fair while for the engine to warm up too.

My W213 had electric louvers in front of the rad to speed up engine warming

 

[EmilysDad]

My W213 had electric louvers in front of the rad to speed up engine warming

My Cortina MKIII had a piece of cardboard in front of the rad to speed up engine warming .....

 

[peterws1957]

My Cortina MKIII had a piece of cardboard in front of the rad to speed up engine warming .....

The Go To accessory for decades, way back when.

 

[Blobcat]

My Cortina MKIII had a piece of cardboard in front of the rad to speed up engine warming .....

But where is the money for the manufacturers in that?...

 

[LostKiwi]

My W213 had electric louvers in front of the rad to speed up engine warming

My 129 has 5 litres of heat generating V8 to aid in coolant warm up

 

[cheapshots]

Thermostat is part number A2742000615 from Merc £120.

I'm going to try and do it myself; if it looks too complicated I'll take it to my local garage.

Failing all that, I'll get me some cardboard

 

[MBDevotee]

Only problem with that fix, is leaning out the window to try and remove the cardboard around town is tricky....

 

[mersum1es]

You can have more sophisticated wind covers than carboard ones:

Maskisuoja | viimasuoja | mersu

Verkkokaupasta edullisesti laaja valikoima merkkikohtaisia Auton Maskisuojia. Ilmainen toimitus yli 80€ tilauksiin. Tilaa omasi nyt!

www.svh.fi

 

[s5tuart]

I can't remember which car it was but back in the day I had one with a little handle inside the cabin that wound a radiator blind up and down
Very sophisticated!

 

[mioba]

I can't remember which car it was but back in the day I had one with a little handle inside the cabin that wound a radiator blind up and down
Very sophisticated!

pure simple mechanics. little to go wrong.

 

[S500 Pete]

But where is the money for the manufacturers in that?...

I am amazed that there wasn't a Mercedes OEM cardboard insert for loads of money

 

[Blobcat]

I am amazed that there wasn't a Mercedes OEM cardboard insert for loads of money

This isn't just cardboard.... this is Mercedes software enabled cardboard...