The wonder truck roars to life.... (PW & M37 Lesson #1 - Don't make assumptions...)


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Posted by Brian in Oregon on August 30, 1999 at 11:00:45:

I finally got the engine running on my 1951 M37. The truck has sat in a barn and a garage for several years after being rolled.

It fired to life and belched out huge thick white clouds every time it was fired. Assummed maybe it was radiator water, like from a leaky head gasket. However, I could only run it for a couple of minutes because the fuel bowl, which I filled by hand, was sucked dry. Finally got a fuel pump working. After running for 15-20 minutes a few times, the white clouds went away. I suspect it is not cooling water but condensation from inside the block. The M37 has a very powerful early form of positive crankcase ventilation. I think once the block just had to run hot enough and long enough to drive the moisture out. No bubbles have appeared in the radiator water and the exhaust does not have that burned antifreeze smell.

Next problem - huge amounts of blue smoke. Looked like an oil-burning steam locomotive. After being convinced the engine would run for long periods without problems, I fired it up and let it run. A thermometer in the radiater never went over 140 degrees, so I figured as long as it didn't overheat, I'd let it run. After 45 minutes, the smoke was markedly reduced. A buddy and I discussed this, and we believe that the heavy smoke was being caused by oil that ran into the exhaust system from when the truck was rolled onto its top. It stayed in this position for at least a couple of days. The heavy smoke was the oil burning out of the exhaust pipe.

I pulled the spark plugs. If the engine was burning oil badly, the plugs should be black and wet. They weren't. They were sooty black and dry. Like copy machine black powder. On a couple of holes only this might indicate burned or stuck valves. On all holes it is an indication of running way too rich. I readjusted the idle mixture setting to lean it out. This also reduced quite a bit of blue smoke (but no black smoke was present unless the choke was engaged.)

The exhaust smelled funny, had a smell that was not burning oil nor burned anti-freeze. That is probably from the old gas I failed to drain and merely added fresh gas to. P.U. Always get rid of old gas.

The truck still smokes, though not as heavy. No doubt the rings are not as good as they should be from sitting so long unused. However, instead of needing a total rebuild, it is possible that all the engine needs is a good deglaze on the cylinders and fresh rings. The engine idles and revs nicely. The rear main seal is puking oil badly, and I don't think I can get my big hands between the flywheel and the block the replace them. Probably have to pull it. If so, I'll deglaze and re-ring at that time.

So, we assumed the truck had a bad head gasket. It didn't. We assumed it was a bad oil burner. It isn't. If you are discouraged, keep at it and find out what the problem REALLY is. It may not be as bad as you think.




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