1999 E300 Coolant loss question
 

My friend has a 1999 E300 that seems to be loosing coolant. He had the system checked for leaks, and the rad cap was suspect. A new $35 cap from Pelican, and it still has coolant loss. I suspect a bad head gasket. Anyone know how to make sure of a bad head gasket? I have heard of a test for combustion gasses in the cooling system, but would that be a definitive test? The engine is not overheating at all, nor is there any external evidence of a coolant leak. Also, he says the engine "shudders" when it is turned off. I think he means that the engine shakes a little upon shutdown. I don't know if this is a related problem, but they both started at the same time. Thanks in advance, Rich

Two areas to check that are not obvious.

1. Leaks into the windshield washer fluid from the windshield washer heater. Anti-freeze will streak the windshield.

2. Slow leak from the auxiliary pump.

Roll guy
 

I have a 95 e300 with essentially the same engine, om606. Mine has just shy of 300k miles and exhibits the same symptoms, and I found the issue. Mine leaks from a o ring imbedded in the head gasket at the rear passenger side. If you look at a new head gasket you will see it. So mine leaks until it is fully hot, which I suspect the head expands just enough to seal, then as it cools in the garage I will get a couple of drips.

No oil in coolant or vice versa. I am making plans on pulling head and sending it to Metric motors for overhaul. I think I can get another 300k out of bottom end it runs so dang good. Not sure if it's the same on yours but check that rear passenger side closely, mine drips on bell housing.

Thanks for the replies! I will be sure to check closely at the washer heater and aux pump. The radiator shop that tested it said there were no visible leaks, so I only assumed it has to be a head gasket. The washer bottle might have been overlooked, so that is the first place I will look once pressure is applied to the system.... Rich

my w210 had a ghost leak too, 8 oz over a period of 6 months. My washer nozzles were dead too (broken elbow connector) - so no streaking to look at.

I did notice that the tank internals looked like an old hard water coffee pot, filled with whitish blue crusty salty deposits. I removed the tank along with the heater and found that little thermostat O rings were flattened and useless.

After that repair I have not lost coolant.


I suspect those mineral type deposits were from the silicated G-05 coolant.

I will be checking that today, and worse case is I will bypass the washer bottle heater. Thanks, Rich

The O rings are easy to change, I swapped them from a dorman O ring selection I have.

The thermostat itself usually doesnt go bad.