I tried a different thermostat and it still doesn't open. Does anyone have any suggestions beyond what was already posted (I tried all of those things already) to get the air out of the system? I already havent been able to drive the car for a week just because I had to replace the hose between the water pump and thermostat housing, now i cant get anything to work right when I put it back together.

I'm quite sure you did not.

As I previously stated, the thermostat was fine. The procedure is flawed. Make sure the front end of the vehicle is slightly raised prior to adding the coolant to the upper hose.

I am quite sure that I did, but I just went and did the same thing again, with the same result. Does anyone else have a suggestion?

.

did you (hot-pot) test t-stat?

if everything checked,system burped,belts tight and upper part of rad hot,
next thing is water pump,...it happened before...no leaks but worn and bad
not capable for producing pressure.

.

__________________
w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered

What exactly is the result?

You take it for a drive and the gauge reads............?????

The gauge quickly climbs to about 3 needle widths past the 80 mark, then I stop and feel the hoses and the upper one is very hot, and the lower one is cold. I will try testing the thermostat next I guess, I have tried 2 different new ones and they did the same thing though.

Would that be about 85C?

If so, the thermostat is functioning perfectly normal.

Most of us find the temperature to stabilize at about 90C. in the head.

You do understand that the head temperature isn't the same as the temperature at the thermostat.........don't you?

There are varying temps thruout the cooling system so it matters where you sense the temp. I'm wondering if you're being overly cautious because it's a M-B. While it's good to be careful I'd push it just a little and see if the temp gage gets to the point of cycling a bit, which is normal. Remember, 100C is the boiling point of water so 80 or 90 is fine, especially given that coolant boils at a higher temp and if you can get some pressure in the system the boiling point rises even more.

I'm more concerned with the failure of the system to build pressure. Is there any coolant loss? There are several ways for a head gasket and/or cracked head/block to leak (into the oil, into a cylinder, out to atmosphere) and some are hard to detect.

With the engine running, are there any bubbles in the coolant (look in the filler neck)? This is pretty diagnostic of a compression leak into the cooling system.

The good news is that M-B engines do not usually have head gasket issues unless they've been overheated. It's probably one of the issues the guys have already raised. After WAY too many years I've learned not to freak myself into thinking the worst - but, of course, it can be.

Good luck on this
Dan

I have been driving the car for almost 2 years with no pressure in the cooling system and no loss of coolant, oil and water mixing, or ever overheating. I know it needs to be fixed, because on any type of hill it runs quite a bit hotter, but I would think if there was a serious issue it would have caused other problems by now. The reason I think there is something wrong is that the gauge reads higher than it ever did in normal driving before, but the lower radiator hose is still cold. What should be a normal reading for the temp gauge on an OM617 once its warm? I haven't ever driven any others so maybe the old thermostat in mine was bad and im just used to running cooler than it was supposed to.

I think you've hit the nail on the head. The likelihood is that the old T-stat was a bit on the cool side and this one is where the factory spec is set. Unless you've had the car since new there's no telling what someone put in there thinking they were "helping" the engine.

If you did the boiling water test you could cook the old one (if you still have it) and one of the new ones and see how they compare. THAT would be interesting!

Dan

I do have the old one, I will have to try it, I guess I will just drive it a little more and see what happens. The one I took out does have a factory part number on it though.

how did you determine the fact that you dont have a pressure?
squeezing the hose or removing the cap while hot?

if the pressure is really missing did you try swap a expansion tank cap?
.... it can be simple as that.

dirty and clogged radiator fins also can produce results like you have
80-85C normal 95-100C under load...

cheers
ChO

.

__________________
w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered

as long as the temp does not hit 120C you are not in danger on the motor, with pressure on the system...
if you do not have pressure in the system, 100C means somewhere in the motor (surrounding the top of the piston) you are boiling coolant.
it's really important to have the system pressurized, unless you want to spend the bucks for Evans coolant... and there are problems with that route as well.
go to the parts store, rent a radiator pump up gauge, and find where the pressure is leaking out.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

A brand new radiator will exhibit the identical symptoms...........to flow more coolant when under load, the thermostat must open further. To open further requires a higher temperature.

No 617 engine can remain at the same temperature when lightly loaded as compared to heavily loaded. It's impossible.

It's not possible to do it twice.

If the head is full of coolant, it will pour out all over the fan when you remove the upper hose.

So, if you managed to do it twice, either it never happened the first time or you have a LEAK somewhere in the system and the amount of coolant in the head is dropping as you drive it.