Ridge,

Why does there have to be pressure in the cooling system to cool? I run my SDs with the radiator caps loose and no cooling problems. One has Evans coolant which is recommended to run with no pressure but the other one has normal antifreeze and water coolant.

The only difference I have noticed is that the heater does not get as hot in cold weaher with the no pressure in the cooling system.

The only need for pressure in the cooling system is to raise the boiling point of the coolant. With Evans coolant, the boiling point is 375F so pressure is never needed. Running with no pressure relieves the stress on all the parts of the cooling system and lengthens their life.

P E H

Yep! The new Evans stuff is pretty neat. The original was a pain, as the viscosity was different and was questionable with stock water pumps, etc. The new stuff drops in and works great, from the few folks that have reported on it. I'd try it myself but so far haven't been able to justify the cost (near $100, last time I checked) compared to just using MB coolant every 3 years ($10). I wonder if it performs the same anti-corrosion function as the MB stuff? Hmm. But anyway, like PEH said, pressure is only there to raise the boiling point. It should run reasonably cool without pressure, or with minimal pressure.

My money is still on the water pump impeller (like in my photos), internally corroded block and/or radiator, or worst case bad head and/or gasket. Easiest to test for the head/gasket problem, get that test kit from NAPA (or similar store) to check for exhaust gasses in the coolant. Or do the simple test, check for high pressure in the system (squeeze upper rad hose) with the car STONE COLD. If the hose is so tight you can't pinch it, sorry, the head has to come off again... :( :( :(

The car made it to Ohio today without any problems.Ran about 95 degrees on the highway in very high temperatures.The temp is still climbing over 100 degrees on big hills.On thing I forgot to mention in my original posts was that after the car runs for a while and is shut off it doesn't start for about forty minutes,I think it may be a dripping injector.Thanks for all the advice, any more would be appreciated.The car went from Colorado to Ohio on Biodiesel!

Climbing to 100-105C on big hills is normal. Tell us again what makes it get to 115-120C?

Driving from Boulder to Nederland,a gain of 3000 feet in seventeen miles .It climbs to 115 in the steepest section of the cayon.