4.0 Weird Behavior After Overheating

[Things2do]

Sorry about the wall of text, but I’ve already tried just about everything that I can think of.

For some background I bought a 1994 Ranger XLT 4x4 for $500 this summer. Clean title, 4.0, 5 speed, 192k miles, pretty much rust free, and supposedly it had a new clutch before it was parked for oil leaks 10 or 15 years ago. Including the tires, the battery, and the starter for which I had no core to return I’m about $1,500 into it in parts. The fan, water pump, and radiator were also missing, so I picked up an automatic radiator with the downward pointing lower hose connection from a junkyard figuring that the cooler might be useful as a power steering cooler in the future.

Last weekend I overheated it pretty badly. I managed to drive about 15 minutes across town without realizing that the lower hose had dropped off of the radiator on a speed bump because its clamp had failed. It was at least 50 degrees outside at the time. I checked all of the other gauges and lights once it started complaining under load, so I still can’t figure out how I missed the temperature gauge. From the sound of the pinging I thought something was coming loose around the clutch or in the transmission, and by the time I parked it even barely touching the gas in neutral was enough to make it ping. The offending bump had a nice antifreeze trail leading from it when I retraced my route that evening.

The engine got hot enough to burn off a lot of the oil from the valve cover leaks and the thermostat is now stuck open. I also think that the heat may have damaged the passenger side motor mount. I put the hose back on, replaced the clamp, waited 45 minutes or an hour for it to cool, refilled it with straight water, and then drove it all the way back without issue.

I’ve read quite a bit about the 4.0, so after driving for 15 minutes without coolant I figured that I had blown a head gasket and/or cracked a head. Well, the exhaust sometimes dumps an appreciable stream of water when revved while cold, and when it’s hot the exhaust randomly coughs and spits out a little steam cloud. Even though it isn’t visibly steaming the hot exhaust has enough moisture to make my hand damp with or without the little steam puff that comes with the cough. But the coolant level hasn’t dropped in either the bottle or the radiator since I got all of the air burped out after refilling it. The exhaust doesn’t visibly steam when it’s warm except for that random tiny puff that you have to be looking for, it doesn’t smell sweet, there is no water in the oil, there is no oil in the radiator, the radiator doesn’t bubble, the rubber glove test was motionless, and there isn’t enough blow by to lift a receipt off of the oil fill. It also hasn’t lost any power. I crawled underneath while it was running and from underneath the engine I can’t hear anything in the exhaust like the little cough that’s audible from the end of the tailpipe. I cranked it with the gas pedal floored to check the compression and it sounds even on all 6. I even misted the spark plug wires in the dark in case one of them melted and was shorting out.

Since it overheated the engine has been vibrating a tad more than it used to at idle, but not by a lot. Nothing like what it was doing before I replaced the old spark plugs and wires.

I have driven it 40 or 50 miles since that happened. I’ve been driving it hard trying to make whatever problems it developed become identifiably bad, but aside from sometimes running a little cool from the stuck thermostat nothing unusual has happened. In fact, after I ran about 60 MPH in 3rd gear for a few miles it almost seems like the exhaust is doing a little less of the coughing and the cold dripping than it was before that drive. I haven’t looked at the spark plugs or ran my little camera down the cylinders yet, but I don’t expect to find anything useful. Other than that I’m pretty much out of ideas. It still runs better than it did with the heavily worn copper spark plugs that it had when I bought it, so I don’t want to tear into the engine unless I’m pretty sure that I’ll find something in there. The check engine light has never come on. It's OBD1 and the bulb does work.

So… What should I check or do next? Or should I just replace the thermostat and then wait to see whether anything gets worse?

 

[bobbywalter]

you start by looking at the plugs.

likely just a good idea to replace them but they might just need cleaned up.

may have uneven valve sealing or some stuck/cracked rings now...or some minor cracks that are fine under normal conditions.

with the even cranking sound though, that is a pretty good sign. the rough running could be a minor vacuum leak from cooking it a bit. that unit should have a aluminum intake but possibly egr. this may have been affected by the heat cycle.

or it never really got too hot and your just freaking out.

they are sensitive to overheating though historically. the castings were better by 94 and then they went to a new setup with new issues.

if its running....and not consuming coolant and copius amounts of oil...and the oil pressure is ok at hot idle....like more then 18 psi on a real gauge...and its not crunching plugs its likely ok.

 

[superj]

the gauge stops reading temp when the fluid drains so you probably didn't miss it reading high, it probably just stayed at the temp it was at when the fluid dumped out.

i had the same thing happen on a jeep. the radiator cracked at the bottom and dumped the fluid. once the sensor tip is not in liquid, it stays where it last read. the whole time i was driving thinking all was good till it started knocking, just like you had happen

 

[bobbywalter]

the gauge stops reading temp when the fluid drains so you probably didn't miss it reading high, it probably just stayed at the temp it was at when the fluid dumped out.

i had the same thing happen on a jeep. the radiator cracked at the bottom and dumped the fluid. once the sensor tip is not in liquid, it stays where it last read. the whole time i was driving thinking all was good till it started knocking, just like you had happen

not really. it can see temp and will vary...still hot in there. ...provided it is variable...

 

[Dilligaf1]

Or should I just replace the thermostat and then wait to see whether anything gets worse?

That's what I'd do, and just not take any long trips for a couple months. Pull the plugs when you replace the thermostat, make sure nothing is burning lean or too rich. If it was still running rough after that, you could get a 1994 Powertrain Control/Emissions Diagnosis shop manual off of e-bay like This and start chasing down whatever sensor/valve that got partially cooked and is sending weird data. I couldn't even point to any direction because I could think of a half dozen things it could be just off the top of my head and you just be throwing parts at it.