I had a coolant leak from behind the engine. After much deliberation and investigating, it turned out to be the intake manifold. I replaced the gaskets and got the upgraded plenum plate from Hughes Engines. On starting the truck, it sounded better than ever. However, after taking it around the block it started having a rough time. By the time I got it back to the garage, it was again leaking coolant.

I also noticed copper shavings in the reservoir. Some googling indicated this is some type of stop-leak that is commonly used to plug coolant leaks. I felt very good about the intake, so I didn't think it was leaking. Also, the key, I noticed bubbles in the reservoir, which is usually an indicator of a blown head gasket. I guess when the Intake Manifold was up to full strength, the next weakest link in the system gave, which was the previously "stop-leaked" heads; by the previous owner I'm guessing.

So replace the heads I did. While they were off I took them to a head shop and they milled them and checked the valves and all that good stuff. I broke off several exhaust manifold bolts, which getting them out ended up being about 80% of the hours I spent working on this, brutal.

So after this, I fired her up and she ran well, and no leaks whatsoever! But after cruising for a bit, I started noticing the temperature climbing and climbing, making me nervous. Then I could hear a clunking once we got past about 220-230. I pulled over and let things cool down. No issues for the first quarter mile, then temperature up and the clunking again. Limped home like this in about 3 stops.

I should mention that I had no heat to the cabin through all this. I'm 90% sure that it's not the water pump because the radiator hose had fluid going through it. I also don't think it's the thermostat because I replaced that when I did the Intake and things seem to be moving as expected.

Can anyone please help me figure out what part of the cooling system is the most likely problem?

 

There should always be coolant flowing through the heater core. It might be blocked or you might have another problem - bad water pump or thermostat?

Is the thermostat in correctly?

 

Thanks for the quick reply 00DakDan. I've read a ton of your posts and you always have great advice.

Well, I'm 99% sure the thermostat is in correctly because I remember being extra special careful with the Haynes manual right next to me when I installed it spring side down. Regardless, I think this may be my first step in the troubleshooting process, to take a look at the thermostat by removing the radiator hose.

If the water pump is not working, then I would think that the radiator hose would stay empty. Or am I incorrect to think that?

 

There would still be water in the hose, just moving fast enough to cool the engine.

Some guys have had their water pump disintegrate.

Could be a bad thermostat too. There are a lot of bad parts out there nowadays. Make sure it is a name brand or get it from a dealer.

 

Try temporarily removing the thermostat completely. If the stat' was causing it, the engine should now run cold.

 

I would pressure test your system. Or try bypassing
the heater for a test and see it stops over heating.