My '97 Jeep XJ Cherokee w/ 4.0L inline-6 engine runs a little hot and it overheats when driving on the highway for longer then an hour. The coolant temp slowly creeps up until it boils over. I've seen it boiling and puking out of the radiator cap, so I know it's not a bad sensor/gauge. There's two fans: a mechanical fan w/ clutch, and a small electric fan that only comes the coolant temp rises above 215*. The electric fan works and is running when it's overheating.
I've replaced the:
- water pump
- both radiator hoses
- radiator cap (tested that it works and holds the right pressure)
- mechanical fan clutch
- thermostat (new one is Stant SuperStat 195*)
I've also flushed the cooling system more times then I can count. The iron block has rusted because the old coolant sat in there too long. I used, in order:
- Blue Devil Flush additive
- Prestone Flush additive
- Oxalic acid (wood bleach mixed with water)
- Evapo-rust Thermocure (did this just a few weeks ago)
After all that I'm sure that the rust has been removed from the system. I replaced the coolant with about 30% anti-freeze and 70% distilled water and 1 bottle of Water Wetter coolant additive.
Last Thanksgiving, it was unusually hot the day I drove 3 hours to my parents house, and the damn thing overheated. So... problem not solved! I was able to get home by airing up the tires to 40 psi and driving at 65 mph.
Maybe the head gasket is blown?
To test for a blown head gasket:
- I used a radiator pressure testing tool (rental) to see if there was a leak. It held the pressure perfectly fine for several minutes.
- I used a testing tool (rental) to test for combustion gases in the coolant. It looked fine.
- There is no white smoke coming out of the tail pipe. No milky fluid in the oil.
- The coolant seems to get brown very quickly, but I don't know if that's because of the rust or from exhaust gases.
Do you think I could STILL have a head gasket leak?
I have a compression gauge at home. Can I use that to check for a blown head gasket??
When I was flushing the cooling system a few weeks ago with the Evaporust Thermocure, I was finishing up putting fresh coolant back in and getting the air bubbles out. Coolant started flowing out of the radiator cap port before the thermostat opened (normal) so I put the cap on and waited for the stat to open. Once it did I took the rad cap off and when I did I noticed some smoke and/or steam came out of the radiator. ???
Winter is almost over and I want to fix this problem before it gets worse. If it's not a blown head gasket I'll replace the radiator again - I replaced it before doing all the rust flushing so maybe rust has plugged it up a little - and swap the mechanical fan for an electric one.
[update] I sent an oil sample to Blackstone Lab and they said there was signs of coolant in the oil. I took the head off and it was warped so I had a machine shop fix it and look for cracks. Put it back on with a new Felpro head gasket. Went for a test drive and it