marpelto

Hi...

You can see that the temperature fluctuates fast. What can cause the issue?

--The Thermostat itself
--Thermostat electric drive (there is a heating element inside the thermostat and it's driven by 12V)
-- Water pump
--Temperature sensor?
--When the issue is ON, no hot air comes inside.

I already replaced the thermostat..it was a half day job as it's under the intake manifold. But the issue persists.
As it's intermittent, I have strong feeling that it might be an elecrical issue. Bad connector of broken wire.

Hey Hoser

Check water pump, definitely

marpelto

The isue is intermittent. It can work without any issues for long time. Then suddently overheating is back.
If it's the waterpump (shaft broken etc. ) this would be permament, right?
But to rule out that, I guess I could open and invastigate it.

Hey Hoser

Are you able to scan the car, see if any codes are showing?

when my water pump failed, there was also intermittent overheating, and the pump started to make a whining turbine-like sound, which disappeared after pump replaced

There are multiple threads in MB forums about W246 overheating, thermostats and water pumps, hopefully some of these may also help.

marpelto

Only P021700 The coolant temperature of the engine is too high.

I need to take a look at the waterpump. It may be tuff to access

marpelto

yes..I agree. Although not the pump itself but the linkage and valve it's attached to.

Apparently the pump has integrated valve that closes by vacuum when cold for engine to warm faster. Once warm enough the vacuumpump reseases the valve. However..these linkages and arms gets stuck once activated and the valve stays closed resulting overheating.

I have not taken it out yet as it's under the turbo..in really tight spot to work with. I may need to remove a lot of parts before accessing the pump..

Let's see...

Hey Hoser

Good Luck!

I consider this project "ambitious", I would never attempt myself, after seeing mechanic's work done fixing my overheating.