79 300CD losing coolant and overheating - PeachParts Mercedes-Benz Forum

Chris p · #1 06-02-2004, 09:38 AM

I need some help from you guys. I purchased a 79 300 Cd sight unseen from Arizona and am working through the numerous problems. I thought I had solved all of my problems but now after replacing the radiator and water pump I am reaching the end of my rope. My exact problem is the radiator will sputter out little drips of anti freeze when I drive the car and eventually in about 50 miles I am on the verge of overheating due to the loss of coolant. When I got the car I had the transmission rebuilt, the heater servo does not function so I routed the heater hoses so I can run the defroster and get hot air. I then replaced the water pump and the radiator and removed the thermostat. I have no problem with the temp the car runs at. It is just this darn loss of anti freeze. I am very frustrated because the car is such a great car and I bought it for my 16 year old daughter to drive but I can't let her drive it in fear she will overheat the car and ruin the engine. I am hoping you all might give me some guidance before I do something drastic and get rid of the car.
Thanks in advance for your help.

P.E.Haiges · #2 06-02-2004, 10:06 AM

Chris,

Sounds like you might have a blown head gasket. See if there is any coolant in the oil, look for water droplets on dip stick. Look for traces of oil in the radiator or overflow tank.

Have a pressure test done on the cooling system. This is where a air pump with gage is connected to radiator or overflow tank. Air is pumped into the cooling system and you can tell by the pressure gage if there are any leaks by a pressure drop on the gage.

If you have to take the head off, you might want to consider a valve job and new valve seals too.

P E H

Chris p · #3 06-02-2004, 10:25 AM

Thanks for the input but there is no coolant in the oil. and if anything there seems to be allot of pressure in the radiator. I put a new mercedes radiator cap on at the time of the radaitor replacement. My mechanic did say something about maybe the head gasket might have been installed improperly. The engine had been rebuilt prior to my purchasing it. I didn't understand how this could cause the problem but that doesn't mean he is not right. The previous owner had run straight water in the cooling system and made a mess of the water pump and radiator.

P.E.Haiges · #4 06-02-2004, 10:54 AM

Chris,

Pressure in the radiator could be from the head gasket leaking. There should be very little pressure below the boiling point

Are there any traces of oil in the overflow tank or radiator. You might have to take off top radiator hose to check for traces of oil.

Usually when you are loosing coolant, I mean internal to the engine not an outside leak, its something wrong with the head gasket or a cracked head.

One other check I just thought of is to run the engine and look for any bubbles in the overflow tank or an increase in the level of the coolant when the engine is revved up.

I'm not sure how a head gasket could be installed incorrectly but its possible.

If you have a mechanic that works on your cars, why don't you tell him to fix it and see what he says?

P E H

Chris p · #5 06-02-2004, 11:13 AM

Yes the radiator over flow hose does seem to bubble or spit coolant when running at highway speeds. I have been telling my mechanic to fix it but I am wondering how far I want to go and I was hoping for something like a miracle simple cure? I have had the car for three months and have driven one tank of fuel through it just driving to and from the shop.

P.E.Haiges · #6 06-02-2004, 11:47 AM

Chris,

I just noticed that you removed the thermostat. Why?
The thermostat has nothing to do with the coolant loss problem. MB Diesel engines are designed to be run with a thermostat and it should not be removed.

Sorry, there is no quick low cost fix for a leaking head gasket. It must be replaced and the head checked for warp and cracks when it is off.

Don't give up now. This shouldn't be that expensive of a repair after all you have already done to the car and it will give many years of service.

P E H

Chris p · #7 06-02-2004, 12:25 PM

The thermostat was removed early in the repair process, before the water pump and radiator replacement and I plan on putting it back in when I finally get this darn car working right. I would also like to replace the heater servo so I can have a normal heating system but first I have to solve the mechanical problems. I will be dropping it off again today to have my mechanic do what he needs to to make the engine sound. Actually I will be trading as my mechanic is putting a new heater fan in my 350 SDL. Contrary to what you might read about my 350's engine I think it is an awesome motor and love that car. I have all summer before I need to deal with the heater. Thanks for the input.

TonyFromWestOz · #8 06-03-2004, 08:01 AM

This is sounding more and more like a head/head gasket problem,
The high pressure in the radiator is the key.
In a couple of earlier cars, I had head gasket leakage. The symptoms of this aer that the coolant system gets pressurised and loses coolant, The coolant changes colour (mine started green and ended up almost black) and eventually, you lose the water pump and other aluminum due to the reaction with the combustion gases in the water. Eventually the head gasket deteriorated so much that I couldn't go 10 km on it.

Chris p · #9 06-03-2004, 08:19 AM

Yes I am afraid I will be dropping the car off tonight to have the head gasket replaced. Last night I tried to drive the car with the radiator cap loosened and at highway speeds I have about 20 miles before I had lost most of the coolant. I appreciate your input and when it is fixed the car should run for along time.

Jimmy Joe · #10 06-03-2004, 03:22 PM

I hope this isn't redundant, but I would again replace radiator cap and thermostat after gasket fix; once these things have been over heated/pressurized, they can't be trusted to perform correctly.
I hope you have finally solved your problem and can now enjoy the car.