Intermittent Cooling Issue

[glcaines]

My M151A2 has an intermittent cooling issue. When I first obtained my A2 the temperature gauge never went above 120 degrees on the dial, until one day the radiator boiled over. I removed the thermostat cover and found that there wasn't a thermostat installed, which explained the low temp readings. I thoroughly flushed the system. The flush water was relatively clean. I topped of with 50/50 coolant and drove the A2 several hundred miles with the temp gauge reading normally. Then one day the temp gauge shot up to maximum and the radiator boiled over. I pulled the thermostat and tested it, and it functioned properly, opening and closing at the correct temperature. I filled the coolant system again with 50/50 and have driven the A2 several hundred miles since without issue. Then, today the same thing happened. I drove the A2 about 40 miles without issue. The outside temp was 68 F. The engine was shut down about two hours. When I was about 10 miles from home on the way back, the radiator suddenly boiled over again. The temp gauge maxed out. I waited a few minutes and ran water over the top of the radiator and removed the cap. I filled the radiator with water and drove home about 10 miles without issue. The cooling system operates fine for long periods of time and many miles, and then this happens. Any ideas?

EDIT: I should also mention that I have pulled my M416 trailer with the A2, heavily loaded, in 80 deg weather for about 50 miles in the mountains, and no overheating.

[Horst]

Initially when I got my A2, it would sometimes overheat a little, sometimes not and then one day completely overheated with water boiling.
Flushing the radiator did not help at all.

Finally I pulled the head and found that some of the water passages between cylinder head and block were clogged. After removing that blockage the engine did and still does run as it should.

In my case the engine had run only a few hundred miles since new but it was the long time sitting in Barstow which caused the clogging.

If that is your problem too, of course I don’t know but that’s what happened with my jeep.

[m3a1]

Junk in the engine block.....almost certainly. The other question you should be asking yourself is, how much of it is presently clogging up your radiator?

[Cobra5]

Sounds like part of your problem was fixed, i.e. temp reading after installing a thermostat but it still randomly overheats. If you don't know the history of the vehicle assume the previous owner was having the same issue and that removing the thermostat was an attempt to get it from overheating. Apparently that didn't work and that's why it was sold. I agree with the others that it sounds like a blockage somewhere in the cooling system. If you have a infrared thermometer take some temp reading at the top radiator hose and the bottom radiator hose. You'll need to get the vehicle up to operating temp and above idle. Set up a fan a few feet back from the front of the radiator. This will simulate air flow coming into the radiator as if you were driving. Your temp readings should be noticeably different. This is the easiest thing to check.

[rickf]

A fan in front of the radiator will not even come close to what the engine fan is pulling through there. If the fan shroud is in place that engine fan will pull more than enough air to cool the engine. The laser thermometer is the best idea and in addition to the radiator and hoses be sure to go over the block top to bottom front to back on both sides. That will give you an indication of dead spots that are clogged. Those clogged spots will generally look cooler that the rest of the engine low down in the water jacket and hotter up near the top. Most of the heat produced is in the head and upper cylinders. If the bottom of the block is packed with rust and mud there will be no water there at all so it will look cooler up till the point of boiling over.

[m3a1]

I picked up a laser thermometer for VERY cheap at Harbor Freight last week and they have extended their 'Black Friday' sale through Sunday so you might be able to pick one up for less than $20.

[steveo]

Did you locate your coolin issue?

I just recently replaced my head gasket as it was bubblin on the passengers side at #3 and I can say I agree for sure with Horst and Rick on the engine water-ways blockage issue. I was not runnin hot but fixin too. The water ways at the gasket passages were all about 50% or so blocked with gunk and rusty chunks. This included the passage at the gasket itself. The block drain passage on the drivers side rear was clogged not allowing me to drain from there till I cleaned it out. The whole clean out process on the coolin ways Took some effort and some patience. Some of the larger material was collected at the rear of the block. Fished the bigger debris out with a telescopic type magnet and the rest eventually flushed out. Don’t forget to flush the radiator too. I was kinda amazed at the amount of junk that came out.
Keep us updated on what ya find.

[rickf]

Whenever you flush a radiator you need to take it out and turn it upside down and flush it from the bottom. This is a reverse flush and will push out crap that is caught in the top of the tubes. When I do an engine flush I will put the chemicals in there to do their job but when it comes time to run the engine I will take the top radiator hose off and let it run out on the ground from the block while adding water to the radiator to supply the engine. This prevents all the crap that is loosened up from clogging the radiator.