I have a 1993 Explorer 4X4. 4.0 Pushrod V6. It has been leaking coolant for a few weaks, so I put some leak sealer in it and it stopped for a couple of days. Now its leaking again, I cant see the leak, nothing hitting the ground. But I do notice , after the engine is hot and I turn it off, a hissing sound like water hitting a hot surface. (Duh). It seems to be around where the thermostat housing is, or on the very right side (passenger) top of the water pump, because I can see a small amount of water on it. Could i just need new hoses? Or is it the water pump? I am ruling out the thermostat because the upper hose is hot. Any suggestions?
I just did this job on my 1991 Explorer 2wd, and it was a leaking thermostat housing (along with a bad thermostat inside) spilling coolant all over the top of my water pump, and being flug by the belt all over the intake tube and other parts. I could eventually see and hear steam shooting from the bottom of the thermostat housing and the truck was overheating bad with all the lost coolant and no circulation. It sounds like you're having the same issue since you saw coolant on top of ur pump (the thermostat housing is directly above it) and you were losing massive amounts of coolant. Take off and inspect the upper radiator hose for leaks . If the hose is the problem (you're a lucky sob) and have a quick fix. If the hose is good, you're gonna need to replace the thermostat housing ($24 Compression Works at autozone, comes
with paper gasket) and thermostat ($6 Duralast at autozone, comes
with rubber gasket attached). Both gaskets are crucial to sealing up that housing chamber. You DO NOT need any sealant.
Repair: Make sure u have good light, you'll need to disconnect neg battery cable, drain coolant (can reuse if good), remove air tube, you already have upper radiator hose off, remove belt, and you can get to the three housing bolts pretty easy. The bolt on top right and bottom are easy, the top left is a little harder. It sits right up against the belt tensioner (which u DO NOT have to remove) and will require maybe a deep socket with small extension on a small ratchet and some finagling. If it gives u a hard time, dont lose patience. I was able to get that bolt off by having the socket slanted and not even all the way on the bolt. There was also a cable running down to the crankshaft right in between that bolt and the housing pipe that is a pain and will be in your way. You should be able to move it slightly to get a little more room.
My old housing
As you can see, the thermostat housing was seriously in need of replace, the top had corroded so bad and when i took it off, it was bulging in a couple of spots, and there wasn't even a paper gasket on it! There musta been some kind of silicone sealant instead. :/
Now once u have the housing off, you'll see the themorstat poking out. PAY ATTENTION to how it is installed, with the the small hole (air relief valve) at the top and the bar on the thermostat horizontal, as u want to install the new one the same way. Try rotating the thermostat with small flat nose plyers, or something u can grip the bar with, to loosen it up a bit (spray a lil wd40 on the rubber edges of the thermostat , it'll get in there and help u rotate it). Take a small screwdriver and put it behind the bar on the thermostat, tap the screwdriver with a small hammer or something to pry and pop out the thermostat
Old Thermostat
You can see the rubber gasket that goes around the thermostat is pretty much gone, and just nasty. And it is all rusted up from years of running water periodically in the cooling system.
After you have that old thing outta there, stuff a rag in the engine opening, and clean off any gasket or rust residue with a degreaser and a gasket scraper if necessary. Also a good time to clean off any coolant residue that got on ur pump or any other parts of ur motor while you have good access in there. When ur finished cleaning, put a lil wd40 on the edges of the new thermostat and install with Air Valve at top, make sure its nice n snug in there. Install your new Thermostat housing
with paper gasket. The gasket might require some patience. It was easiest to insert the top right bolt through the housing with the gasket on and attach to engine, screw it in slightly with ur fingers, and align gasket with other holes and put other two bolts in slighty with fingers. Screw them in nice n slow, you don't want to rip that new paper gasket. Tighting down bolts evenly and torque to
10 ft lbs. If you dont have a torque wrench, just make sure they are nice and tight. Take a moment to admire the new nice looking thermostat housing you just put on and pat yourself on the back, if you will. Reinstall your belt, upper radiator hose, intake tube, add your coolant back , and reconnect battery. Double check your connections before you start it back up. Your leak should be solved!
Total cost should be about $30-$50 bucks for parts and coolant, maybe 3-4 hours depending on the cleaning required. I ended up replacing the upper radiator hose, and belt while i was in there, as they were badly worn as well, as well as cleaned all my pulleys before i put on new belt (I was using belt dressing for awhile and that stuff gunks up all over them). And buy some latex gloves for $2!
P.S. If your upper hose was hot, that confirms the water pump is working. And your leak probably stopped because of that leak sealer u added before. I guess somehow its working at the moment. It has been 4 days since i did this repair and everything is cooling great and I have no more leaks. I'm going to eventually replace the thermostat sensor also. If you have any problems or need any more help message me. Good luck!