Mj Newbie Help With Cooling System

[jeffheffe]

Hello,

 

I have a 1987 Comanche 4.0 6cyl 4x4. I am not very mechanically inclined, but in owning this truck, I'm trying to learn as much as I can!

 

My truck continues to overheat. I've replaced the plastic coolant tank cap, and then the whole tank. A hose near the heater control valve recently blew and I bypassed it. Now its overheating again and I'm not sure why.

 

I've been reading all over the site, looking for a diagram and step by step details on how the cooling system works for this engine. Any help at all would be appreciated! Thanks

[mvusse]

Does it overheat in stop and go traffic or idling in your driveway, or does it overheat running 75mph down the highway?

[jeffheffe]

It will overheat running, or in neutral. Yesterday we flushed the radiator and pulled the thermostat. Previously replaced the plastic coolant tank. Still gets super hot. This "closed system" is messing with me! Half the hoses are boiling hot, and the other half are fine. Going to check out the heater core hoses today. Thanks

[ncmountainMJ]

Best thing you can do is tear it all out and replace with a later model open system. You can find the radiators pretty cheap if you look online. My local auto parts had one for around 100 bucks and I use a plastic jug as an overflow. works great and keeps around 210 on hot days. Best mod by far IMHO.....

[ComancheKid45]

Have you bled the cooling system at all?

[ftpiercecracker1]

1. Make sure the front of your radiator is clear of debris, like leaves, dead grass and whatnot. This wil stop airflow and inturn cooling.

 

2. Take a look at your water pump do the fins look good? It is extremely rare for the fins to break off or wear down, but i have seen it, albeit it was not on a commanche. If you don't want to remove your pump I have heard of/and done the surge test, but never really liked it. If you want to try this instead of pulling the pump, start the truck, while keeping it running, using your hand squeeze the top hose as tight as you can, ineffect cutting off coolant circulation, and see if you can feel a "pressure" or a surge of coolant when you release the hose after a few moments, if you do feel this and are sure of it, your pump is most likely NOT the culperit. But like i said i don't really trust this method, but its easy to do.

 

It will overheat running, or in neutral.

 

3. This sounds like your fan clutch could be shot. To test, start truck and let it idle until it gets warm, say 190* roughly, then turn the truck off, pop the hood and try to spin your mechanical fan. If it spins with very little resistance, like super free/multiply revolutions, your clutch is shot. If when you try to spin it and you find resistance and/or it will not make a full revolution using its own momentum your clutch is probably still ok.

 

4. Not bleeding the system can/will cause overheating as well, Look in the DIY section for a great way to do this.

EDIT: Here is the link http://comancheclub.com/topic/11684-bleeding-your-closed-cooling-system/page__hl__bleed

 

 

5. There are some other things that can causing overheating, like a blown head gasket and clogged catalytic converter but i would start with the above first.

 

EDIT: What exactly is your temp gauge reading? Remember these engines are designed to run between 190* and 210* which would feel "boiling hot" if you were to grab the hose with your hand.

 

I would also have flushed the block, forward and back.