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02JagCat.
I recently had a 3.0L 200 hp efi rebuilt. Runs great, but overheats after shutting down. It has new water pump and housing, poppet valve, etc. It only happens after I’ve been idling awhile. I thought that maybe the probes were wrong, but checked the temperature with a temp gun. The temp is correct. It never overheats while running, just after shutting down. Any ideas?
It’s obviously a sensor in our opinion. It could also be trash in the thermostat clogging flow.
Since you double checked the temp the block is heating up when you shut down.
On the rebuild was the thermostat replaced? Reason I ask is the water is leaving the engine block too quickly after shutdown without cooling off the cylinders or cylinder head. Or as BCB suggested there may be blockage of the water ports.
Let us know what you find.
Just a thought. Because coolant flow stops immediately when the engine stops running, gasoline engines have heat soak for up to 10 minutes after shutdown. As Bass Cat said, maybe you have a sensor that is being tripped by the heat soak and you are seeing that normal temperature rise on your temp gun.
Two new thermostats, water pump and housing, plus a new poppet valve. It is going back to the mechanic today, he believes it is the poppet valve. We will see.
My first guess would be poppet valve. If it sticks, it will let water drain from the block pretty quickly. T’stats are at the top of the block, so it is not likely the problem is up there. If it is not poppet, I’d be hard-pressed to offer another guess assuming your temp measuring of the block is right. Note do NOT measure in the center on the back. That carries exhaust out and it will definitely get hot. Measuring the heads should give you a good idea of temp, just don’t get too close to the exhaust path in the middle. If the head temps are good, replace the temp sensors on both heads.
Not that is is not that uncommon to have one head reading hot, other reading normal. Computer won’t like that. Even if it is not crazy hot, that will trip the alarm.
Thanks old-timer, I measured the temp at the cylinder heads, right were the temp probes are installed. The two agreed within a degree or so. I sure hope its the poppet valve, the mechanic did say he had an issue installing it. Hopefully I will know soon.
My 225 Opti had similar overheating after shutting down. Also had some erratic temps while idling. Water pump was less than 6 months old but when I took things apart I found that the base plate gasket was blown out. Replaced everything and it was good after that.
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