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Overheating suggestions?

1987 Cherokee with 4.0L and automatic transmission overheats all the time. I have replaced the following: Radiator Temperature Sending Unit Thermostat Thermostat Housing Heater Core Recovery Bottle Cap Fan Clutch Spark Plugs Spark Plug Wires Rotor Distributor Cap

I have also had the water pump checked and the coolant checked for exhaust gasses. Both passed fine.

I can bleed the air out of the system and it will do fine for one run cycle. However, when I turn it off and let it cool, the next time I start it will start the overheating again. The overheating gets progressively worse with each hot\cold cycle of the engine until I bleed the air back out of the system.

I can get heat out of the heater and can see the coolant moving in the recovery bottle. The upper and lower radiator hoses are also hot. Thus, the thermostat and water pump are known good.

No evident leaks of coolant while sitting, unless its started overheating, in which case it comes out of the recovery bottle at the cap.

Any ideas, or is it time for the scrapyard? I had the head gasket replaced awhile back, and one mechanic mentioned that they might have blocked a coolant passage, and thoughts on this random thought?

Thanks guys!

-Kurt

Reply to
Kurt C. Hack
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I am missing something here.

How are you 'bleeding' the air out of the system?

Once you have flow to the heater core and the recovery bottle, the air is gone.

Are you sure your temperature gauge isn't just bad? They are well known to not be very accurate.

Do you have the coolant in the bottle near the bottom of it when cold? If overfilled it will piss out on the ground until it finds it's proper running level to allow for hot expansion.

In other words are you sure it's overheating?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

"Kurt C. Hack" wrote:

Reply to
Mike Romain

I am bleeding the air out by jacking up the rear of the vehicle and removing the temp sensor at the back of the motor until all the air escapes and only the coolant is flowing.

The temp sender has been replaced and I have checked the value coming from it compared to what the gauge states, so the gauge and the temp sender is known good.

I have gone through the process of letting the system "right" itself after refilling and bleeding the system. After that its OK for the first run cycle. However, after letting it cool overnight its starts the process again of overheating. The problem becomes progressively worse until I refill and bleed the system again.

Thanks,

-Kurt

Mike Roma> I am missing something here.

Reply to
Kurt C. Hack

You are implying you are leaking fluid somewhere?

Otherwise 'refilling' doesn't make sense unless that is just after a blow over.

So you are getting air somewhere, somehow into it. A waterpump with almost no blades left can maybe aerate the coolant and put bubbles in. The bubbles then go and get stuck in the head causing it to overheat. Unusual, but it can happen.

Did it start doing this after any particular work was done or were all the parts below in response to the overheating.

Something like the fan clutch comes to mind. They make two that will fit on that engine. One id reverse of the other. Same for the waterpump, they make two versions.

I have seen and heard of the wrong pump or clutch being in the 'right' box too...

The serpentine belt engine uses reverse rotation parts. The V-belt engine uses the normal parts.

Mike

"Kurt C. Hack" wrote:

Reply to
Mike Romain

The fluid I'm leaking is coming back out of the reservoir after an overheat condition. The more run cycles I go through, the more more coolant loss as a result of the progressively worsening overheating.

I have replaced the clutch fan, but even the new one never seems to "lock up", even during the overheat condition. However, I am just idling the engine in the driveway since its up on jack stands right now for other issues. Thus, the only heat hitting the clutch is that drawn from the radiator by the fan and the ambient heat from the engine. The old clutch exhibited the same behavior. I have considered tack welding the clutch fan in place to make sure that it is engaged all of the time.

This engine does have the serpentine belt.

Thanks,

-Kurt

Mike Roma> You are implying you are leaking fluid somewhere?

Reply to
Kurt C. Hack
Reply to
Matt Macchiarolo

This is a closed loop system with the pressurized resevoir. The radiator seems to be getting hot evenly and I have the same problem with and without the thermostat installed.

Thanks,

-Kurt

Matt Macchiarolo wrote:

Reply to
Kurt C. Hack

When the engine is hot, watch the fan when someone shuts down the engine. A good clutch will stop the fan almost instantly. My new one on my 88 will for sure.

If it doesn't, it is the wrong clutch. They do make two kinds and both fit.

Otherwise I would be opening up the waterpump for a quick look. If it's ok, then RTV silicone works to seal it back on.

Mike

"Kurt C. Hack" wrote:

Reply to
Mike Romain

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