Intermittent overheating after cylinder head rebuild

[Pete M]

1 minute ago, derf said:

He put in a lower temp thermostat so in theory it shouldn't run that hot.

 

 

thermostat doesn't control the upper range, only the lower range. 

[Airborne Janitor]

Water pump was replaced 7 years ago. I am contemplating getting a flowkooler replacement, I've been running one in my XJ for years with good luck. 

 

I need to get my temp gun to confirm temps, but I drove this truck last year without issues until the head gasket started leaking....

 

I'm running 3.55 years with 33s which sucks but is doable, I have 4.56s in a box which I'm going to install once I fix this overheating issue. 

 

I'm going to try burping the system again at the temp sensor in a bit. 

[derf]

2 hours ago, Pete M said:

 

 

thermostat doesn't control the upper range, only the lower range. 

Sure, but an engine should get to an upper limit above the thermostat rating and stay there for the most part.

 

If you're getting to 240° something else is wrong.  It's one of a couple of thing.

 

1.  Corrosion inside the block that prevents heat transfer to the coolant mix.

2. Corrosion or sediment in the radiator preventing heat transfer to the air.

3. Insufficient water flow.

4. Insufficient air flow.

5. Too much heat being generated by the engine for the cooling system to handle.

 

#5 usually happens when you add forced injection to a naturally aspirated engine, but also can happen working then engine hard (possibly when its running lean).

[Airborne Janitor]

So on the drive home tonight I took the state roads, average 50-55mph. Stayed right under 210* unless I was stopped at a light, then it would go to 210, then drop back down on acceleration. I bled the air at the temp sensor tonight, the truck ran right around 185-190* for 30 mins. After turning her off and tightening the sensor, I turned the vehicle back on and the gauge was at 230*, then dropped down after a few mins. 

 

Will grab my temp sensor tomorrow and report back. 

[derf]

You will get higher temps shortly after shutting down.  The coolant will soak in residual heat and spike a little.  As soon as you start it running again the pump will push cooler water through and should bring it back down in short order.  So I wouldn't worry too much about that.  Focus on temps while driving and idling.