Overheating 4.6L? Not sure... HELP

[soylentgreen]

Okay, so my 98 4.6L RWD is giving me a problem. The temp gage stays pretty low for a long time, then it will get up to "normal" quickly...then suddenly jump to the top of the range. Temp light comes on too. Then, with continued driving (or even turning the engine off briefly...just a few seconds), the temperature will go back to normal and stay there for the duration.

I thought it could be the themostat is acting up...sticking. So, I replaced it. The problem persists.

Also...the heat will blow hot when the temperature is in the "normal" range...but cold at all other times. In other words, even when the engine is supposedly overheating, the heater blows cold (both front and back).

Now I think either the system has an air pocket in it or the water pump is doing some weird gymnastics. I've never seen anything like it. I'm fearful that it could be a head gasket too.

Any opinions or fixes or known issues would be appreciated! Thanks!

 

[soylentgreen]

Bump.

 

[Big Brian]

I would verify that it is actually running hot

When its cold, start it and let it warm up and monitor the temp by touching the upper radiator hose.

Cou8ld be nothing it wrong and you have a bad temp sensor

of course using a handheld thermometer of some kind would be the best way but it doesn't sound like you have that

 

[1955moose]

I was conferring with my friend, he concurs you've got an air pocket that needs to be removed. The best way is with a adapter cap on the expansion tank where you fill the coolant. Apply vacuum it will suck that air pocket right out. You might get lucky doing it with front end elevated, and running it squeezing on top hose, but that may or not work. Also replace the tank cap, their cheap enough, and why guess. My guess is someone did cooling system work recently!

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