Coolant loss Diagnosis???? Cracked Something? - PeachParts Mercedes-Benz Forum

Couper · #1 10-13-2012, 05:15 PM

I'm losing about a gallon of coolant/water in about 30-40 miles of driving in about every couple of days. No more leaks from hoses and newer thermostat. I get a steady stream of coolant vapor from the overflow tank bleeder hose adjacent to the cap at operating tempurature (80-90C)

The most troubling test I ran is that I get a steady stream on large bubbles from of overflow reserved tank when 300TD is running with cap off. I needed to completely top off the reserve tank to get the bubbles. I guess it needs to be full to see bubble coming from hose coming from radiator.

Is this a definative sign that I have a cracked block, head or blown head gasket?

Are there any other test or symptoms to observe to confirm that the head needs to come off?

jay_bob · #2 10-13-2012, 05:27 PM

With the engine cold and the cap tight since it was warm, pinch the upper radiator hose. If the hose is firm, or when you open the cap it releases pressure that is a sign of a breach in the head (gasket or crack).

Couper · #3 10-13-2012, 05:54 PM

I just put the cap on and started the cold engine. Just a few minutes later the upper radiator hose is firm and the coolant gushes out when I open the cap.

So it's definate?? At best, my head gasket is breached?

Also, my resently replaced resevoir tanks is all cracked. I guessing from all the pressure from system.

jay_bob · #4 10-13-2012, 05:58 PM

Leave the cap on overnight and come out in the morning when the system is stone cold.
Then check for pressure.

Couper · #5 10-13-2012, 06:43 PM

I'll check it again tomorrow morning.

What is a colder engine going to tell me? It was pretty cold when I checked for pressure build up early. I was running for just a few minute over a couple of hours ago when I discovered the bubbles when cap was off.

It looks pretty bad. I bought the car with a warped head. I had help and was very careful Removing and Replacing the head. I'm having difficulty accepting it, but I'm thinking that the head gasket is leaking. It is only showing up now, just a few months later and just under a 1000 miles of driving.

jay_bob · #6 10-13-2012, 06:52 PM

The theory is that when the engine is warm and the head is compromised the breach opens up and then combustion vapors enter through the breach and mix with the coolant. When the engine cools and contracts the breach closes up, and the vapors try to leave the coolant but have no where to go, thus keeping pressure on the system when cold.

In a normal engine you have 100% liquid (except for maybe a small air pocket at the highest point of the system) that expands as the engine heats up and contracts when the engine cools. When the engine is cold there is no pressure.