Ok so I got a 300M with a broken timing belt. Pulled the heads, every valve was bent, not surprising since the belt let go at 4K doing a high speed pass. Ok So the heads are trash I get replacement heads from Odessa, put them in have a few minor problems but get it all buttoned up. Car purrs like a Kitten but overheats as soon as it's driven at all. I have 150 range compression on all cyl execpt 3,5 which I have 125 range, So I'm thinking I'm blowing compression into the water Jacket, when this thing blows it blows the blow off valve in the overflow goes as well as the radiator cap. Any thoughts, anything else to check ? I"m about to do the second tear down, which I'm dreading like the black death.

Matt

 

Do a pressure test and/or a leakdown test before you pull it down again you could be wasting your time tearing into it maybe it's just air locked. your tstat could be failing it could be any number of things. Did you use a new water pump? Did you just assemble everything and fill it with coolant from the tank?

 

I would do a pressure test on the cylinders and the coolant. just because you do these tests you could also have a damaged head gasket.

 

Thermostat replaced with part from auto parts store. Car overheated. Installed an OEM themostat from dealer. Problem solved. I think the one from the store was installed backwards, but the tech said that is not possible. He had to do it twice and only got paid once.

 

FYI: I bought mine with "overheating problems" turned out it was the radiator cap and their was air in the radiator system (their is bleeder scre on top of the intake).

 

that's not a 300m engine they are only 3.5 and no bleeder screw on them .

 

HHmmmm....

 

I had a Concorde 3.5 that the pipe ran from thermostat housing under the exhaust manifold to the rear of the engine develop holes in it causing the car to over heat. I fix the leak and after putting coolant and bleeding system my rad developed a leak. Replaced it with new and decided to replace thermostat at the same time. Again the car over heated. To make a long story short, I had installed the thermostat in wrong. Installed it the right way and the car purrs. Tempted to take motor out and put it into my 300M Special but I have another 3.5 Special engine I'll rebuild and make sure this time I put the thermostat in right.