Mercedes-Benz Forum banner

1 - 6 of 6 Posts

·
Registered
94 S350, 06 E320CDI
Joined
·
929 Posts
Discussion Starter #1 (Edited)
I have a 1991 350SDL that I have been semi-restoring. I have replaced many parts on it and it has been running great. I don't drive it much and recently when I took it out, the coolant light came on.

The coolant level is fine before I drive the car. After the car heats up, the coolant level light goes on and the coolant level is low. The coolant level goes back to normal after the car is turned off.

The car does not overheat while running - it stays close to 80 degrees even in Houston summer traffic. The radiator does not have any cool spots.

Pertinent stuff I have replaced while restoring are:

Radiator
Thermostat
Temp sensor in the head
Water pump
Auxiliary Pump
Coolant level sensor
Coolant reservoir
New Coolant cap
Heater Core
Heater Valve
All new hoses

All parts genuine Mercedes


All of these parts were replaced a few months back and the car drove at least 50 miles with no issues before this started happening. I haven't driven it much since. It doesn't get driven much anyway, but I hesitate to drive it until I know what is happening.

I have not gotten to replacing the temp sensor on top of the engine where the top radiator hose goes yet.

I don't know what would make the car do this and what might be causing it. I know cars pretty well, but this has got me stumped. Any ideas out there?
 

·
Registered
1991 350SDL, 2004 Honda Odyssey, 1999 Honda Civic DX
Joined
·
11 Posts
Most likely some air is trapped in the system (or one of your new hoses is expanding too much under pressure but not likely), when the temp goes up the air in he system gets compressed and the coolant disappears from the reservoir. Those cars have known head gasket issues too, you may want to check into that.
 

·
Registered
94 S350, 06 E320CDI
Joined
·
929 Posts
Discussion Starter #3 (Edited)
Air in the system is actually my top choice. What is throwing me off there is that it worked fine for about 50 miles of off and on driving. If air is there, it would have been in there since the radiator install and coolant replacement. I don't understand why it would have started after a while.

Also not sure how to get it out. It normally just comes out after driving for a while especially if you turn on the heater.

The thermostat actually has a pin in it that I thought was supposed to help with air in the system.
 

·
Registered
94 S350, 06 E320CDI
Joined
·
929 Posts
Discussion Starter #4
ok, I got it resolved with a pressure tester. One of the heater core hoses was loose and I didn't know. It was causing the fluid level to drop when pressure increased. It may also have induced an air bubble.

It has been fixed. On with the restoration!
 
1 - 6 of 6 Posts
Top