91 overheating

Any chance you have the thermostat in backwards?

Did it begin when when the exhaust was replaced? I have not had this particular problem yet but while researching MY overheating problems I read that a blocked catalytic converter could cause overheating.

I'm about to replace my radiator and fan clutch in a few minutes. I'm pretty sure my fan clutch is bad (it turns freely when the engine is hot and I never get that "whoosh" sound any more) and my radiator is clogged. If that doesn't work I'll be doing all the other things that you did (not sure about drilling holes in my thermostat though) so please post any progress you make and solutions you may find. I thought I'd solved the problem on my '92 but the temp gauge went up while I was going up a steep hill. The rest of the time the temp gauge barely moves. I put in a new thermostat not very long ago. I guess I'll have to yank it out and test it. At least it's not dumping coolant any more when I shut off the engine. My '91 is close to being undrivable right now unless the outside temp is 90 F or less.

That theory seems like it fits the facts. The thermostat would still work, but delayed since heat would have to conduct thru the body of the thermostat to reach the expansion capsule part of the thermostat. The capsule is supposed to be immersed in the hot water of the engine block. So the spring side goes toward the radiator, the capsule is on the hot side and expands and pushes the valve open against the spring.

By drilling holes in the thermostat, hot water from the jacket is able to jet against the capsule, causing it to expand and opening the valve. That explains why the holes help, and why the engine even overheats in very cold weather- it's going to be a lot harder to get that capsule hot enough to open if it's on the cold side, and the cold side is below freezing.

I think Ashton's right.

-Paul

That theory seems like it fits the facts. The thermostat would still work, but delayed since heat would have to conduct thru the body of the thermostat to reach the expansion capsule part of the thermostat. The capsule is supposed to be immersed in the hot water of the engine block. So the spring side goes toward the radiator, the capsule is on the hot side and expands and pushes the valve open against the spring.

By drilling holes in the thermostat, hot water from the jacket is able to jet against the capsule, causing it to expand and opening the valve. That explains why the holes help, and why the engine even overheats in very cold weather- it's going to be a lot harder to get that capsule hot enough to open if it's on the cold side, and the cold side is below freezing.

I think Ashton's right.

-Paul

Well, my fan clutch was all oil and goopy on the thermostat and there was so much mud on the radiator that it was probably only working about 15-20%. Considering that I now have 3 Exploders I decided to just go ahead and put in the new radiator and keep the old one for a spare.

I went up some steep dirt hills in 4WD with the AC on and now the temp goes up about halfway (100 F here today) and then drops back down to about one forth of the way up. It will now idle at a stop with the AC on without overheating. That's a big improvement but I have not given it the windy mountain road test yet.

Thanks for the try -

The thermostat is in the correct way. I have tried a couple of thermostats over the past couple of year. It took a while to figure out that three holes were necessary to make it work - two holes were not enough.

Randy

Not sure about right after the exhaust work. When it was done, the temperature gauge stopped working. That was replaced and all seemed well at that time.

We don't use the truck very much the past couple of years - about 4,000 miles a year.

The temperature problem became evident when we pulled out pop-up camper on a trip that ended up abruptly in West Virginia when the pump blew out on the transmission. Stupid me had the transmission rebuilt instead of junking the truck. Since then any time you go over 2,200 or so RPM - the temperature climbs about 30 seconds after you hit the gas.

The radiator hoses are also new and don't appear like they could collapse. I havent found any that have the coil spring inside like some others.

Any other ideas?

I had a pickup that would sound like it was overheating when I shut it off, you could hear the coolant start to boil. I replaced the radiator cap and that fixed it. Since caps are cheap and you've tried most stuff I give a new cap a try. You should also consider the fan clutch, the difference between good and bad doesn't feel like much to the "hand" but can make a big difference. On my old mustang a new clutch cooled it down about 20 degrees and changed it from nearly overheating on a hot day to running like it should. You may have already done this stuff, I don't recall the start of the thread.

Those holes can't let thru nearly as much hot water as an open thermostat. Is there an obstruction or something that's keeping it from opening? Is it sticking and then popping open? Try putting the thermostat in a pan on the stove and see how it opens. Stick a meat thermometer in with it to measure the temperature at which it's opening. They usually start opening at 180 degrees F. It should be wide open as the water nears boiling. You can also try installing a 160 degree thermostat. That might solve your problem by brute force.

I just can't believe that three little holes work if the thermostat is installed properly and working properly.

You say "Hit the gas and watch it jump for a minute or two and go back to where it started." That seems to eliminate the rest of the cooling system- it wouldn't heat up and then "go back to where it started" after a lag if it was the radiator or waterpump. It sure sounds like there is a lag in your thermostat opening.

-Paul

First of all *most* of us have had the transmission repaired/replaced and I have no regrets (did it on 2 Explorers, 91 and 92).

Ok, here's what I did, for what it's worth. I replaced the radiator and cap on both Explorers (both were overheating and boiling over the reservoir after the engine was shut off. The '92 was billowing white smoke when it was first started in the morning. I replace the fan clutch on the '91. On BOTH I added a can of J&B Stop Leak. The '91 is now pretty much perfect except the new fan clutch seems to be causing a lot of noise. The white smoke is gone on the '92 and one time going up a hill the temp gauge went up to about halfway and then went back down. I think the thermostat may be sticking open most of the time so I need to check that.

The reason I used the stop leak in new radiators was to try to determine if there was a coolant leak in the heads or someplace. If there was the J&B seems to have stopped it. I'm thinking I was getting some exhaust into the coolant on both Exploders and that was causing air pockets in the coolant and bubbling in the reservoir. I also think my radiators were clogged.

The J&B stop leak says it fixes cracks heads and leaking head gaskets. I don't know how long it will last but for $5 I'd say it's worth a try especially if it is barfing coolant out of the reservoir after you shut it off.