Overheating puzzle

[jpcoutts]

I've had overheating issues with the J20 almost as long as I have had it (since 2005) and my efforts to fix the issue have included a new radiator and cap, new fan clutch, hoses (with spring in lower hose) and thermostat. Today the air temp was in the mid 70's and on a short run to town around 10 miles each way the truck got hot and was spewing coolant out of the overflow onto the overflow tank. The engine has about 75K on it and is in good shape as far as I know. The factory shroud is in place. When I start the truck in the driveway and let it warm up to operating temp with the cap off I can see good flow through the radiator. I am at a loss about what is causing the overheating. Any thoughts or suggestions ?

[jpcoutts]

Is there a good way to test a radiator cap? Maybe mine isn't holding pressure.

[DBX11]

Rent a Cap test kit from autozone Or maybe plug the vacuum advance to see if maybe you have too much advance.

[wiley-moeracing]

If your boiling out the coolant, you may want to check for a blown head gasket or cracked head.

[MysticRob]

Pressure check the entire system and see if you have a leak somewhere in the system. You can never rule out hot spots due to blockages and/or sludge elsewhere even with all the work you've already done.

I discovered a badly corroded freeze plug on the driver side of the block. When I hammered out the old freeze plug to replace it I could see a huge amount of sludge in the block's rear coolant passages from an apparent lack of good coolant flow. That hot spot is now flushed out thanks to blasting it with a garden hose, but who knows what lurks in all the other coolant passages of my block.

I have yet to start mine with the cooling system filled and functioning (started engine only once to check carb rebuild), but figure I'll be getting the entire system flushed with a good machine to minimize that issue.

[letank]

collapsing return hose -the lower hose used to come with an inside spring to prevent this effect-


also some have reported issues with the flow kooler pump, too fast and the coolant speed tricks the thermostat which closes too quickly


so may be your thermostat is defective, test it and test any new thermostat...


as for the radiator cap, look at the integrity of the gasket



As said time to pressure test your system


it is a 360 right on the 258 some pumps have a reverse rotation!

[jpcoutts]

A really strange thing happened after I drove it about 6-8 miles to pick up a load of firewood last night, it was spewing out of the overflow tank and after a few minutes it cooled down and the top hose collapsed after being fine before I left on the trip. Me and the other expert mechanic there thought the thermostat might be stuck.

If your boiling out the coolant, you may want to check for a blown head gasket or cracked head.

Good thought but I checked the dipstick and no sign of water in the oil. At the risk of sounding like a parts changer I think I'll put in a new thermostat and try a new radiator cap just to see if that will take care of the problem.

[Ristow]

You got a blown head gasket or something else putting combustion gas into the cooling system. You dont always get coolant in the oil.

[jpcoutts]

Is there a better way to check besides a compression check?

[letank]

Is there a better way to check besides a compression check?

pressure test the cooling system, you can get a free loan from autozone tool loan program, I think other parts store do it.

Remove radiator cap and pump about 8 psi... the system should stay pressurized... you can probably go to 10 or 12 psi, our systems are rated to 16psi.


As for headgasket leaks there is a chemical test... done will the engine is running and the radiator cap is off


https://www.harborfreight.com/combustion-leak-detector-64814.html?cid=paid_google|||64814&utm_source=bing &utm_medium=cpc&utm_campaign=&utm_content=&msclkid =9ebe34b5806f17ea064b6b1f5cbde387

[rang-a-stang]

I had a van blow a head gasket and it showed those same symptoms (overheating, "boiling" coolant, oil looked good, etc.). The gasket can fail between a coolant passage and the combustion chamber. No oil involved.

Caps are cheap and not worth testing IMHO. I would just buy a new cap. You will spend more money in gas going to rent the tester, then finding it's bad, then back to the store to return the tester, than if you just bought another cap.

I am with wiley-moe and ristow; you have a blown head gasket. You need to do a compression check.

Oh, MysticRob, that sludge you saw was probably casting sand. If you read SC/397's engine builds he always spends time picking it out once the heads are off. I have probably pulled 2 cups of it out of my block between my 2 rebuilds. The first time I got about 1.5 cups out. Second time (this time) about another .5 cup. It's usually really thick around cylinders 7 and 8. It is AMAZING how much crap is stuck in there, even from the factory.

[MysticRob]

Oh, MysticRob, that sludge you saw was probably casting sand. If you read SC/397's engine builds he always spends time picking it out once the heads are off. I have probably pulled 2 cups of it out of my block between my 2 rebuilds. The first time I got about 1.5 cups out. Second time (this time) about another .5 cup. It's usually really thick around cylinders 7 and 8. It is AMAZING how much crap is stuck in there, even from the factory.

Wow, surprising to hear that. I have no idea what kind of shape the cooling system was in before I bought it, but the radiator was bone dry and had evidence of leakage everywhere. Lot of caked rust in the old hoses too, so figured it was taken care of as well as the rest of the poor old girl. Thanks for the info!

[letank]

Caps are cheap and not worth testing IMHO. I would just buy a new cap. You will spend more money in gas going to rent the tester, then finding it's bad, then back to the store to return the tester, than if you just bought another cap.

Pressure testing does not test the cap, the cap is removed from the radiator, it tests the integrity of the cooling system. I agree buy a new cap, it is made with poor quality materials, so the rubber fails after a few years...

Interesting fact about the casting sand... it is a common talk on the diesel forums ... I never bothered to remove the block drain plugs in the back... my temperature has stayed within the normal range... but it is something to be checked for those who have temperature issues

[jpcoutts]

A few days ago I got the radiator out along with the fan Yesterday I flushed the radiator as well as I could by running clean water through it with a garden hose. Then I did the same for the block by running the hose into the upper radiator hose. On both I let the water run until it came out clear. Not the best but there aren't any radiator shops locally to do a proper boil out anymore. I'm going to wait for it to warm up a little bit today before I put the radiator back in and refill the system. I guess I better hope nothing bad happened with the 19 degree low temp last night since I'm sure there was some water left in the block even though the lower hose was off and the truck is parked on a slight slope to the front.

[jpcoutts]

Frustration is my new middle name! Yesterday I put it all back together and there was a massive leak at the t-stat housing. Today I went and got another t-stat gasket and put that in doing my best to be sure everything was in its place. I put the top hose and by-pass back on, filled it up and water began pouring out somewhere around the t-stat housing. It got dark before I could find where it was coming from. I'll try again tomorrow.