Excessive Pressure without overheating - PeachParts Mercedes-Benz Forum

Sako83 · #1 04-05-2004, 05:46 PM

Before a month i had my 230ce 88 model head done by expert mercedes mechanic.Now after a month i notice that there is excessive pressure in the water hoses.After a trip i parked the car and next day i checked it and there is still pressure and water came out when i opened the cap.I went to my mechanic and he told me it is normal,then i went to other mechanic and he told me there is something wrong.So what do you think guys?Is it normal to build pressure in the water system and remain the pressure on it after day???The temp gauge of the engine is not exceeding 80c and i dont have any overheating problems.

G-Benz · #2 04-05-2004, 05:56 PM

The two simplest (and cheapest) things to look for is the thermostat and the expansion tank cap.

The fact that your temp is not exceeding 80C indicates that the thermostat is stuck open...your engine is designed to run between 85-90C and the other management systems use that temp range as a barometer to set other parameters...

...or the thermostat you currently use is too cold (opens too soon). If it is stuck open, when it fully fails, it will close up for good...then you WILL have an overheating problem.

Check the condition of your coolant cap. It's designed to maintain pressure. If you aren't overheating, it's probably doing it's job, but it may also be the incorrect cap pressure (too high, which would result in lower temps, but excessive coolant pressure).

Both the cap and thermostat run about or less than $30 (even at the dealership). The thermostat should be the 87C version, but I can't remember the BAR specs for the cap...

Sako83 · #3 04-05-2004, 06:11 PM

my radiator cap is the original one and can maintain high pressure its written on it 140.Also i changed my thermostat when the head done and its 87c.So am i going to use other radiator cap less than 140???

Sako83 · #4 04-05-2004, 06:16 PM

How the combustion gas pressure leaks to the water system???How i could observe it?Is it safe to drive on high pressure when there is no overheating??

whunter · #5 04-05-2004, 06:35 PM

Quote:

Originally posted by Sako83
my radiator cap is the original one and can maintain high pressure its written on it 140.Also i changed my thermostat when the head done and its 87c.So am i going to use other radiator cap less than 140???

140 on cap is for 140C not 140psi........
The cooling system can contain 14 - 16 psi on average, any more and damage can occur.

stevebfl · #6 04-05-2004, 07:41 PM

Actually the 140 on the cap means 1.4bar or about 20psi. Some caps say 120 and that means 1.2 bar or about 17psi.

Haven't seen any 100 caps in about 20 years. That would be about 14.2psi.

Lower the level in the reservoir and see if there is pressure after it is cold. There should be a small gaseous pocket above the coolant in the reservoir even when hot. If the tank is full cold it will presurize just from thermal expansion as it heats.

Sako83 · #7 04-06-2004, 01:58 AM

I bought a new cap also 140,because i didnt find anything less.So i will try my car today with the new cap and watch the pressure.

Sako83 · #8 04-06-2004, 04:04 PM

Still the same after i changed the cap.I dont know what to do???is it possible to build pressure from faulty water pump???What are the symptoms of faulty water pump?I need your help guys.Thanks in advance.

G-Benz · #9 04-06-2004, 04:10 PM

I'm beginning to believe that you are indeed experiencing the symptoms of an impending head gasket failure...cooling components are functioning and maintaining proper engine temps, but excess combustion chamber pressure has managed to leak into the system.

It is probably marginal right now, but it will only get worse...I'm not the absolute expert here, but if this is the case, more driving could eventually cause the engine to overheat and possibly warp the head...you don't want that.

And if enough coolant spills into the cylinders, you could hydrolock the engine and maybe even bend a rod...more $$$!

Sako83 · #10 04-07-2004, 05:02 AM

I went to other mechanic shop and he told me that the pressure is not normal and something wrong with the head gasket.I went back to my mechanic who done the head before a month,he told me not to worry and everything is normal till the temp is ok.So i dont know what to do??Is it possible that wrong head gasket insallaion cause a pressure?

Ferdman · #11 04-07-2004, 07:12 AM

Sako83, how did you conclude that the mechanic who replaced your head gasket was an "expert Mercedes mechanic"? Does he guarantee his work? If so, I'd ask the second mechanic (who verified that you have a problem with the new head gasket) to call the expert Mercedes mechanic and explain his diagnosis. Then have the expert Mercedes mechanic perform whatever rework is required to make the job right ... at his expense. For future work go elsewhere, maybe to the second mechanic.

Fisherman · #12 04-07-2004, 07:47 AM

It is sometimes hard to get the results you need in a situation like this but frankly since this problem started right after installation of a new head gasket then guess what? More than likely it is the new head gasket unless this was a problem that had developed before and this is why you did the head gasket. In which case the head gasket was not at fault and you are now chasing the problem still.

Anyway, you may or may not get satisfaction from this mechanic but I agree wth ferdman, have the 2nd or even go a third reputable mechanic and if he finds the same issue have him call the first guy and explain his diagnosis. If he balks, go to another perhaps until he gets the picture...

just my .02

G-Benz · #13 04-07-2004, 10:59 AM

Did the tech that installed the gasket replace the head bolts too? The bolts are designed to "stretch" when properly torqued, and are one-time use only parts.

Reusing the head bolts is a definite no-no, and since the old ones won't stretch with torque settings upon replacement, they can and probably will work themselves loose and breach the head.

michael cole · #14 04-07-2004, 11:05 AM

i dont get it.if the system is pressurized during normal operation without any coolant leakage implying a tight sealed system wouldnt that same system maintain that pressure for a period of time ?

G-Benz · #15 04-07-2004, 11:14 AM

Quote:

Originally posted by michael cole
i dont get it.if the system is pressurized during normal operation without any coolant leakage implying a tight sealed system wouldnt that same system maintain that pressure for a period of time ?

How do you know there isn't any coolant leakage?

If the head gasket is beginning to leak, not only does combustion pressure find it's way into the cooling system, but some trace amounts of coolant should begin to leak into the cylinder heads as well. Not much at first, but if you keep driving it like this, the failure could be abrupt!

If the exhaust has white plumes, it's a sure sign of coolant being burned during combustion.