Coolant sensor bad and boiling coolant

[M. Robbins]

I started getting a "Coolant Sensor Bad" on the display every so often on the display. Now, every once in awhile, after I turn off the engine, boiling hot coolant is flowing back into the antifreeze resivior.

I took it into have a mechanic do a computer diagnostic on it & nothing showed up! The only thing they could find was tht the radiator cap was the wrong pressure. Changed out to the right cap, but now the "Coolant Sensor Bad" display and boiling coolant flowing back is starting to happen again.

The only other suggestion the mechanic had was that I might need a $2,000 head gasket replacement job? ARRRGH!

Any other possible solutions?

[pkucan]

Year and model would help?

The radiator may be clogged or the water pump is not pumping?

You should be able to rule out head gasket with a compression test.

Are you going to replace the sensor?

[fredjacksonsan]

Diagnosing cooling system issues is usually pretty straightforward. The first thing is that the bad temperature sensor might not be telling the fans to come on, which would let it overheat in traffic or around town [but it would be ok on the highway]. I'd replace the bad temp sensor first; if you could answer the questions below it would help:

Have you been you using any coolant; as in you've had to add it frequently?

Is coolant leaking out anywhere, when the Jeep is parked?

With the radiator cap off, if you let it run awhile will you see flow going across inside the radiator?

Does the cooling fan come on once it is hot?

[mastertech1964]

the coolant sensor bad your seeing displayed is for the level sensor in the overflow bottle its not gonna be related to your boil over issue