Overheating Issue

[aPanzerIV]

Hello all,

I bought a 1998 Frontier with a well-overheated KA. I had the head machined and pressure checked, tossed a gasket set on it, head bolts, thermostat, water pump, and a few hose clamps, and it ran great for about 1500 miles. (by great I mean as good as possible with 90psi comp and 20* timing.)

Then at the end of a 3 hour drive or so (all highway and hills) the temperature gauge went from normal range to fully pegged in about 20 seconds. I shut it off and coasted into a gas station, but by the time I it was stopped it was already back in the normal range. I waited 30 minutes or so, popped the cap, and put maybe a quart of water in it. I started it up and let it warm back up, didn't see any leaks, and started driving. About 5 minutes later it did it again. I stopped, it cooled down, I got it back to my house (only another mile away).

The next day I got a flush kit, new fan clutch, and a thermostat. I put the old one in a pot of water on the stove and it seemed to work, the old fan clutch was also tight. An un-alarming amount of crap came out with the flush. I let it run for about an hour to be sure the system was bled, took it on a drive, got about 20 or so minutes out and it went from normal range to pegged in 20 seconds, and cooled off just as fast again. I played the game of pulling into gas stations and parking lots and letting it idle around the parking lot to see when it would do it for the whole day, but it wouldn't overheat unless you were at speed.

I got home and let it cool off completely, got a multimeter out to test the temp sensor and when I started it up it finally started burning coolant. The sensor tested good so I hopped back in to the auto store, I didn't even get out of the driveway before it was overheating again. This time there's water in the oil so I parked it.

What went wrong here? Poor headgasket installation? Warped block? Cracked cylinder wall? This was my first time doing a head gasket but I took it slow, kept everything clean and torqued the bolts correctly. What could I have missed? Is the block likely salvageable?

[Desert Rat]

My 98 never overheated even when crawling in 4lo in 110 degree temps. It was rock solid, so yeah, you have an issue, and coolant in the oil points to a head gasket issue. If it got good and hot, any of the possibilities you mentioned could be the issue. Block might be OK, but the head could be toast. That said, these motors are cheap in the wrecking yards and you might be better off dropping a complete JY engine in.

[whomadewho]

If there is coolant in the oil the main & rod bearings are probably gone. Could be a cracked head or an internal crack in the block. I wouldn’t mess with it. Check your radiator hoses could nave one that is collapsed?

[amc49]

New motor time. People just can't grasp that commonly, and for sure if the overheat is deep enough, both the head AND the block crack or warp. Saw it more times than I can count when I worked garage long ago and now the engines use much thinner wall casting procedures to save material making it even easier to happen. I myself NEVER buy a car with a very overheated engine, just too much possibility of losing your butt on those.