Coolant over-pressurizing after engine turned off... heat soak?

[Squamish_Steffen]

Occasionally, after driving and turning the engine off, within 2-3 minutes the engine bay starts to smoke and crackle. Popping the hood, its clear that the coolant reservoir is dripping from below and the drops fall directly onto the hot exhaust pipe exiting the engine, thus smoking/smelling/crackling. It last about 5min. During this time, the oil temp reads at max too!

The drops are about 2 sec apart. So even after this has happened a few times lasting for a few minutes each time, the overall coolant level does not appear to be low.

This has happened only two in the last month, with no correlation to driving intensity, driving time, or outdoor air temperature that I can tell. Seems random.

While driving or any other parking I have never seen the oil temp gauge rise above the midpoint. Engine otherwise feels/sounds healthy.

I explained the issue to a local mechanical. He "pressure tested" the coolant system to 18 psi or whatever and said there were no leaks or other signs of malfunction. I don't think he probed very hard into the issue.

I have not fully inspected the water pump but from the outside I see no signs of leaking.

Sounds like some kind of heat soak right? Like the engine can't clear its residual heat after being turned off. But its a mechanical water pump so of course turns off with the engine.

Any ideas??

 

[03GoingStrong]

Well, one possibility that comes to mind is a faulty thermostat. Maybe some rust and debris in the coolant system causes the thermostat to stick occasionally. Don't know when the last time your system was flushed but maybe it's time to flush and refill the system? Or maybe the thermostat is going bad, in which case it should be replaced. There are other things that could be causing the intermittent condition such as the water pump as you mentioned, but based on you description, the thermostat just pops into my mind.

Also check condition and proper tension of your fan belt(s). That water pump needs to be turning when the engine is running.

Thermostats are easy enough to clean and check. Just plop them into a pan of water on the stove and heat the water until the thermostat pops open. The hard part is getting to the thermostat and of course there is the dealing with the loss of coolant in doing so ...

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[LibertyTC]

Check the reservoir cap is it a 16psi? Also look at the bottom of the reservoir gasket to make sure no cracks or tears.

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Has the water pump ever been replaced? If it has more than 120,000km, I'd consider changing it anyways.
Flush very good idea, and always use the Mopar thermostat for your kJ, the black ring is the sealing gasket & has the air bleed hole built in.
Would also be a good time to consider replacing hoses.

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Mopar Hoat or Zerex G-05 coolant only to be used for our Kj's.

 

[Squamish_Steffen]

Thanks for the thoughtful replies folks!

Reservoir cap is 16 psi indeed. Coolant is pink/red. Water pump appears to turn fine with the engine speed.

I don't have the full service history of the vehicle unfortunately. But its at 125 miles now so perhaps time to renew some minor components such as hoses and thermostat. I have more faith in the water pump for some reason but may do it anyway if draining the system...

Next time it happens I'll also start the engine again to check the cooling systems pump etc. I'll report back if anything interesting arises.

 

[tommudd]

I've removed water pumps that barely had any blades left on them.
I remember 5-6 that way people brought to my place with overheating issues
changed everything else but thought since WP wasn't leaking it was fine

 

[Royy]

Thanks for the thoughtful replies folks!

Reservoir cap is 16 psi indeed. Coolant is pink/red. Water pump appears to turn fine with the engine speed.

I don't have the full service history of the vehicle unfortunately. But its at 125 miles now so perhaps time to renew some minor components such as hoses and thermostat. I have more faith in the water pump for some reason but may do it anyway if draining the system...

Next time it happens I'll also start the engine again to check the cooling systems pump etc. I'll report back if anything interesting arises.

When you drain the system, make sure you get a complete flush, and then fill it with the proper HOAT coolant. HOAT is always yellow/orange, so whatever you have in there now is not the proper coolant for the KJ.

 

[tommudd]

When you drain the system, make sure you get a complete flush, and then fill it with the proper HOAT coolant. HOAT is always yellow/orange, so whatever you have in there now is not the proper coolant for the KJ.

Not true on color
It is usually yellow
BUT,.......
it also comes in pink, blue, red and orange which leads to a lot of confusion, since many just go on color instead of really checking
One way , well another way is to look for GLOBAL on the jug, manufactures often refer it as global on the packaging
and will indicate that it meets G-05 requirements

 

[Squamish_Steffen]

It turned out to be the radiator fan motor!

Strangely, it didn't fail out-right, but was working intermittently. But when the clip reads 12V and the fan doesn't spin despite free blades, its pretty clear the motor is shot. $180 CAD and 5min swap out in the parking lot. Phew.

I didn't see the pattern at first, but the clue was in the low-speed of previous overheating events. It had only happened after driving for a while at very low speed where the fan is necessary for the radiator to be of any use.