Overflow tank boils over after truck is parked, temperature reads normal

[xzaviergomez]

Okay, I have a 1993 4.0L 4x4 Ranger. I have been having issues with the cooling system. I flushed the radiator six months ago and I have replaced the following:

thermostat (old one was good though)
radiator cap (pretty sure old one was good)
water pump (failed)
bypassed heater core (leaked)

I have not replaced the temperature sensor, but it does seem to function... i.e. it goes from cold to normal as it should.

Anyway, the truck runs fine. I live in Houston and we're dealing with temperatures over 100°. Sometimes, whenever I park and turn off the truck, I can take the cap off the overflow tank, and the water is at the proper level and is not boiling. About a minute later, it starts boiling. Sometimes it boils so much it overflows out of the tank. The temperature gauge doesn't read past normal, though I have seen it get a little higher in the past before the new water pump.

I really don't know what to do. It's worth mentioning that I've been losing so much coolant troubleshooting the radiator, that I started using water instead. I'm going to flush the radiator again today and fill it up with 50/50. As far as I can tell there are no air bubbles.

My main fear is head gasket issues. Anyone have any input? Thanks a lot.

Have a good weekend, guys

 

[BLOODBANE]

I had this problem with a 302 that we had rebuilt. The heads werent torqued to the right specs(used old torque specs), it would run normal temps, but when I would stop it would throw the anitfreeze/coolant into the catch res. I know you haven't done a rebuild, so you may be right on your gasket idea.

 

[adsm08]

Go to NAPA and get a block test kit. Test the cooling system per the kit instructions and go from there.

If your system tests OK, I'd use a 60/40 mix if temps are up over 100.