are these head gasket symptoms?
 

I need some hints - does this sound like a head gasket issue?

suddenly high oil consumption (0,5liter/1000km - about 1qt/620mi) but no smoke from tailpipe. oil consumption before was 0,5liter/4000km

dissapearing coolant but no visible leaks (coolant in reservoir is clear)

low MPG - 18, before it was usually around 21.

All these sympoms appeared after a hard winter.

TIA

NO, but if that is what you suspect check for combustion gases in the cooling system to be sure

The evidence you posted is too sketchy to be certain you have a bad head gasket. I would look for more evidence before completing the diagnosis.

If you are burning coolant, one or more of the cylinders should be suspiciously clean. You may want to remove the spark plugs and take a look at their condition. Oil consumption is still in the acceptable range.

I've had trouble in some cases locating external cooling system leaks on my MB.

The only way to know for sure where it's coming from is to have the cooling system pressure tested. You can hire a shop to do that or rent one from one of the mass-marketers like Pep Boys. If that test doesn't expose the coolant loss, then a cylinder leak down test would help to oncover a leaking head gasket.

Good luck.

How many miles since your last oil change?
Have you switched oil grades?
Are you seeing oil leaks under the car or along the side of the block?
Cleaning of the exaust manifild side of the block, head, and all around the distributor cap area can reveal a common upper timing chain cover leak.
Could also be a valve seal issue.

Yup, I'm just back from my mechanic and I had that tested. It is indeed the head gasket.

also the cooling system was pressure tested and performed OK.
while doing the head gasket I'll have the valve seals replaced and other parts if needed.

Oh, and I'll propably switch to mineral oil - 15W40. I've been using synthetic Castrol 5W40 for the last 3 years and changed to Mobil1 5W50 at the last oil change. I change oil every 10.000km.