Strange overheating!?
 

Howdy All,

My 1987 300D OM603 has begun overheating strangely:

The car is full of coolant. I filled the engine by pouring the coolant into the top radiator hose.

With the car cooled down, it starts and idles fine and warms up as usual: 80-85 degrees. Extended idling does not make the temperature guage increase at all above 85 degrees.

With the expansion tank cap off and all hoses connected and not leaking, I drive the car for maybe three minutes and the temp guage quickly climbs to redline, 120 degrees in less than a minute.

When I stop the car, the engine is obviously hot. The expansion tank has softened and has a pinhole in it now. The coolant level is still full, but the engine makes surging sounds like the thermostat is opening and closing...

Does this sound like a stuck thermostat? Why does the car run cool at idle to 2500 RPM parked, but overheat as soon as it is driven?

There is no smoke or coolant smell in the exhaust and there are no visible leaks in the system. The coolant level only drops a tiny bit from the hot coolant squirting out of the tiny hole in the tank.

I'll keep RTFMing tomorrow and try to discover what the book says about thermostat problems.

Any help would be appreciated...

Thanks,

Kevin

Oh, and I need a new tank...

[With the expansion tank cap off and all hoses connected and not leaking, I drive the car for maybe three minutes and the temp guage quickly climbs to redline, 120 degrees in less than a minute.]


Why are you running and driving it with the cap off?

Howdy. There is now a hole melted in tank. With the cap on, the steaming coolant sprays out the hole.

Would the system not being pressurized cause it to overheat in just seconds? I don't see how..

Thanks,

Kevin

If the water pump impeller had come loose it might turn just enough at idle but not enough at higher speeds.

-Jason

If the spring in the lower radiator hose has rusted or gone away.... the hose will feel ok but can collapse when the car is being driven... you should not be able to squeeze the LOWER hose together with your hand....
Must fix the hole and pressurize the system to hope to find the original problem...

Its likely you have air in you cooling system, if its overheating that quickly. If it was low on coolant for any amount of time, it could have caused air to enter the system. I would start by replacing the expansion tank, then fill the system with coolant. On the 617 its necessary to fill through the upper radiator hose first(disconnected at the radiator) and then top it off through the tank. I'm not sure if this applies to the 603, but it couldn't hurt.

You haven't replaced the thermostat lately have you?

See I know this guy who put a thermostat in backwards once and it reacted a lot like yours.

It DEFINATELY wasn't me. Nope, not me at all. Surely I wouldn't do something like that.

Possible your system cannot achieve the 16 or so lbs of pressure to keep it from boiling due to the hole in the tank...i know my car will spike to hot quickly with the cap off dont ask me how i know...Also try to get this resolved before you crack your likely #14 head if it still original from 1987..
Also need more info.. did you have a problem thats why you had system open?? or just coolant change ...if coolant change you may not have a full system and needs some more water in the engine from top hose....the stat will be closed if engine is not hot and no water will go in..maybe try warm up and pour coolant mixed with hot water through top hose, so the stat will stay open..Good luck

Arlo

I have to break it to you mate but your Cylinder head maybe Cracked, i to had the same problem steam coming out of the radiator fill container and temp Sky rockets fast, end up i had to pay 3K for a new engine, if it goes over 100*C there is a chance of developing a crack in your cylinder head

What Actros617 said put another way, when my 87 SDL displayed that behavior, there were cracks in the cylinder head.

Sixto
87 300D

First you need to replace the expansion tank, you really can't do much until you do that. Than I'd pull out the T stat and either replace it your put your old one in some hot water to make sure its working. While its out check the lower hose and radiator. When you refill the system, refill it through the upper radiator hose.


More diagnostic's are needed.

Cracked head symtoms?
 

Howdy,

Now that there is funny ;>) No, I have not changed any engine parts lately.

Thanks to everyone for the responses! I will replace the tank, pull the thermostat and recheck the bottom hose. My hoses and radiator are only two years old, so that would be weird...

Does the area that cracks on the OM603 heads cause cooland to recirculate through the crack or is it a combustion chamber crack? My compression test shows normal pressures all around.

I've always heard about these heads cracking, and I have replaced two of them. Those cracks were in 20 and 22 heads and were in the combustion chamber.

This is the first time I have experienced cooling system/cracked head symptoms on my own car. I guess I'm due.

The coolant is not foamy or mixed with oil. It is clear and green, so I am leaning toward a thermostat issue. The engine ran cool until the day it suddenly overheated.

Please keep sending me ideas to check on. I'll have some time to work on the car next week and I'd like to get to the bottom of this starngeness...

Thanks again,

Kevin

See how fast it builds pressure when you start it. If its building enough pressure to blow the expansion tank, well you have your answer.

yup...
 

I have had the water pump impeller disintegrate on me before once. That one was made of hard rubber and was not in a Mercedes engine. Aren't these pump impellers always made of metal?

I loosened the top hose while the engine was running and there was flow. It didn't seem like the coolant was pumping very fast, but it was moving...

Oh yeah, there is also another symptom! I have a squeaking noise from the water pump/idler pulley area. That started about two months ago... I didn't think it was significant until now.

Kevin

Sounds like the water pump, tank, and radiator
 

If the water pump is squeaking the bearings are about ready to blow. Sqeaking happened to me and I am surprised that it held together once I looked at it. If it does blow I understand it can be very bad for your engine. Replace it now. It is easy and not very expensive. The squeaking could be coming from the idler pulley or alternator also.

The problem isn't the hole in the tank. There is little pressure at normal (85C) operating temperatures. Still, you need to fix that tank because the temperature does go up when climbing hills on a hot day with the AC on. I haven't heard of anyone patching the tank, but maybe it could be done.

The fact that it runs cool at idle, but overheats when you drive it sounds like the radiator, or degraded impeller on the water pump. The thermostat must be working because it would overheat during idle if it didn't. Turning on the heater full blast might make a difference. If it does, then the radiator is indicated. If it does not, then the water pump, which needs replacing anyway, is indicated.

If the idler pulley or tensioner arm are wobbly you might as well replace them too. And if your belt looks worn, do that too.

Don't use anything but Zerex G05 (or Mercedes) coolant with distilled water. The cheap stuff devours your engine so is a false economy.