if the system is maintaining pressure there is no leakage

The cooling system should hold enough pressure to blow water pump seals nor should it hodl pressure for 2 weeks. That may happen when there is a head or head gasket problem.

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Brian Toscano

My experience has been the weak link, pressure wise, is the radiator, it will be the first to fail under elevated pressures.

The pressure cap will regulate the pressure up to a certain flow rate, then afer that it just can't vent fast enough and the pressure will climb.

A suggestion is to run unpressurized, mostly to protect the radiator, but also as an experiement.

I blew a head gasket completely, oil in coolant in exhaust in oil in coolant...
During this the oil level was rising, it was pumping coolant into the crank. Something else o check. The coolant will be at the bottom, crack your oil drain plug a little and see what comes out.

Thanks guys for your replies.
I'm going to tell you the whole story.Before 2 months the water light flashes in the dashboard telling me that there is not enough water in the tank.So i filled the tank with water nearly 2 litres were lost.Then i drove my car for another 2 weeks till the light came on again,this time 1.5l of water were lost.I went to mercedes benz mechanic who only repair mercedes and has reputable shop.So i had told him the story,he checked the engine and told me that there is excess pressure in the water system and this is symptom of bad head gasket although the car is running great and without overheating.He advised me to first change the thermostat and to watch the pressure for another 2 weeks.After he changed the thermostat nothing differs.i drove the car for another 2 weeks,during that time i was always watching the pressure but nothing changed.Still there were high pressure with water loss.Till that time the engine were running great without overheating and without mixing between oil and coolant.But i was afraid from the pressure so i decided to do the head.I went to him and asked him to do the head.So he started the job.He removed the head and told me that the head gasket is bad at the end of 4th cylinder and that was causing the problem,so he sent the head to machinary shop to clean and check for water pathways(he didnt change the water guides coz they were ok),he cleaned the valves,new valve seals,new Elring head gasket,new manifolt gaskets,new timing chain regulator,new valve cover seal.The cylinder bolts were not changed coz they were ok.So after a one day of work he gave me the car back with new head gasket.From first week i determined that there is a pressure in the cooling system but it was less than before so i neglected it.Before few days i observed that there is pressure in the cooling system same as before but without any significant water loss.So i went back to him and he checked it and told me its ok and his work is 100%guaranteed and he is responsible if anything happens in future.I went to other mechanic and he told me its not normal and there is something wrong with the head.So i dont know what to do?I cant wait till something bad happen to the car.
The mechanic who did the head is expert and daily works on mercedeses specially same as my car 4cyl.But I'm sure that there is something wrong cause the pressure is not normal.So may be something else is causing the pressure?
So what you advise me guys??to wait till something bad happen??

Sako83, have the second mechanic diagnose the source of the high pressure that you are experiencing now. Be sure to mention that the "expert Mercedes mechanic" reused the head bolts. Just because a mechanic works on Mercedes exclusively doesn't guarantee that he knows everything about them or knows all the proper repair techniques.

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Fred Hoelzle

Today while i'am driving the car back to home the water light in the dashboard flashes.So the old symptoms came back.water loss and high pressure.Tomorrow i will go to the mechanic and i hope i can convince him.So if the head is removed do i need new head gasket,new manifolt gasket,new valve seals???or he can use the old one though they are replaced recently(before one month).Do he need to send the head to machinary again?

Mechs see a lot of things & I would still give this guy a chance to solve the problem. Some mechs say you know when you have a cracked head - won't make it down the block. However, in the diesel world we see a "micro cracked" aluminum heads on the early engines that can go for years with funny cooling system issues like erradic temperatures or high cooling sytem pressure before they finally fail. Almost always the problem is identifed as a cracked head.

I'd be interested in seeing what a pressure test of the head confirmed, but it may take a very thorough pressure test at a very good machine shop. As an added precaution the head bolts should probably be replaced. MB says they can be reused if they aren't stretched past the service limit but several mechs have had issues reusing them. Yes, the head gasket needs to be replaced. Usually it comes as a head gasket set and all the gaskets are replaced.

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Brian Toscano

So the problem is maybe from the head bolts???but there isn't any oil leak from the head.So i think the head is tightened enough.I believe that the problem should be from something else than the head.so what about changing the water pump as a try??

Sako83, have a competent MB mechanic properly diagnose the problem before proceeding with any additional work on your engine. From your description the water pump seems to be fine. A faulty water pump would not cause high pressure, more likely reduced or no pressure.

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Fred Hoelzle

Proper diagnosis is a must. If there is high pressure in the cooling system then its got to be coming from exhaust gases. Nothing else pressureizes. I think some people will have a tester to verify the presense of exhaust gases in coolant. But as to why its getting in there, there is something either not sealing between the head and block OR the head is internally damaged (cracked).

Has the head ever been pressure tested?

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Brian Toscano

Today i went to my mechanic and he checked it.Still he consists that there isnt pressure.He advised me to change the thermostat to 65c so it open sooner.So i changed the thermostat and i will try it for few days,if nothing change i will go fo another mechanic and pay from my pocket

There should only be ONE thermostat for your car, and changing the to a lower temp thermostat is a band-aid at best and incorrect. It may be an unusual problem that he's not able to track down so he's telling you it ain't a problem.

It would be nice to know exactly what the machine shop did and if a pressure test was performed. Have you ever overheated the car?

My '87 190DT w/ 379Kmi had a cracked head (4 visisble places) & blown head gasket. Ran GREAT, does NOT overheat. High coolant pressure, oil getting into the coolant, external coolant/oil leak were the symptoms.

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Brian Toscano

Sako: Looks like you are spinning in circles.
1) Do not replace your thermostats with a 65deg.
2) Adjust coolant level to the proper level, leaving an air space in the reservoir when it is hot.
3) Get an exhaust/combustion test strip at your local auto-parts store. ($5.00) and run the test.
4) if the test is negative and you still "feel" there is too much pressure, replace your coolant cap.
5) If you still feel there is still too much pressure, only a leak down test will tell you if the head gasket is defective.
If done properly, an exact diagnostic should be available within one hour.
jackD

After changing the thermostat when i park the car and let it cold the pressure goes(no pressure),but when i drive it and its hot there is pressure.So its a something positive,before that the pressure was remaining even after a day.But i recognise a new thing,when i park the car after a trip,there is coolent next to the container and the system vaporize,So is it normal the system vaporize?

My engine starts to shake when the car is on park or N and there is pressure in the system,but when the pressure goes the car stops to shake.
Today i went to another mechanic and told him the story,he advised me to check the radiator may be its closed and causing the problem.So what do you think guys?May radiator cause pressure?