95 explorer 4.0 I bought it for little to nothing knowing that it had been over heated due to previous owner running it with no thermostate in it. I knew one of the obvious things was going to need fixed , possibly the head was cracked, or maybe the head gasket or intake gasket was going to need work. After six months had passed I made different plans pertaining to projects and needs of mine. Which left the explorer open to ideas or the who cares about it category. So i went and did an experiment with a product that i had never used and out right wanted to test it and it's claims. With the explorer as my ginnie pig I purchased a big bottle of Blue Devil Sealant. I followed all the directions and to my surprise it worked, and worked great. The explorer was running great, sounding great and not one leak of any kind coming from the cooling system. I drove the explorer for the next month or two muddy like I have just told you and was never light on that throttol. The tempore gauge always stayed about one quarter of the distance shown on the gauge marked as normal operating level. Then, with not much warning my Blue Devil began to fail me, and once again the 4.0 had engine coolant leaking issues. But unlike the previous time I now could see directly where it was leaking coolant from the engine, and took all the work of diagnosing and investigating the source/ problem. It was clearly the intake gasket which was the issue at hand and by this time the the dang thing had grown on me. Which meant fixing it, and fixing it the right way. So gaskets were ordered and job was completed. At first I did not notice anything strange or not right about the gasket job that was just completed, and actually the explorer ended sitting a lot and not being used more then a couple days in a two month period. The first time I used it and drove it for a full day I was not getting any heat, and found that the radiator was just low. I filled it, and then had plenty of heat, and the temputure gage steadily sat at the three quarter mark of the gauge that was marked as normal. But I do want to point out, it was way higher then the previous temputure observation while running under the Blue Devil system. So I excepted it visually and ran with the punches, which again had left the explorer on the side lines not being used. Three weeks or so go by and again I was able to use the explorer from the side lines for a full day of adventures. Immediatly I knew that something was different then the time before, I recognized that the temputure gauge was showing an engine that was running very warm, semi hot and once again no heat. I thought, what the heck, I'm pretty sure it was completely fixed and all coolant systems had been topped off with antifreeze. I was clearly in shock and awe over the the idea that possibly my friend had not completely filled up everything and again I was having this no heat and engine running hot issue going on. So I checked the radiator levels and found it very low, with a reservoir completely filled. I poured a completely brand new fifty fifty antifreez one gallon jug into the radiator. Scratching my head, I thought to myself, how odd, with questions it left me standing there wondering if i had a leak some where, was it just not filled completely the time before or something else. After filing it, I had heat and temputure gauge say at the quarter way spot on the normal range line. The next day I was able to use the explorer again and again the temputure gauge was running way high up on the normal line and again no heat. So of course I immediatly assumed it was low on fluid again and had a leak some where. Out on the high way with the gauge border line out of the normal and just a smidge under the red dash that says hot. I felt it was bees to pull over and obviously get some liquid into the old girl , so I started gathering snow into buckets that I had with me while my buddy proceeded to pop the radiator cap off. Which showed me and others that obviously we did not know **** about the situation.
Because all of my antifreeze that I had just put in the day before i believe was now on the ground. I filled the radiator back up with snow water and was able to physically blow the reservoir antifreeze over to the radiator physically blowing it over. I headed hom, and was very nervous concerning the temputure gauge running so hot and so close to the red line and actually over the normal safe zone line. I ran around in the explorer for the rest of the day, constantly watching that gauge and it continued to stay right there in the same area, just pad the normal zone and just under the red hot line.
Next day I bought new thermostate and tested my old one, to find that the old one is completely fine and in good working order. To wrap this up, I'm left at a loss. I have no heat, the gauge shows that I'm running border line hot, visually it seems that I'm running hot, the sounds of the truck sounds like I'm hot, but I can not find any leaks, thermostate is in working order, when shutting off the explorer, one can hear the fluids boiling. So close, so close to that Hot mark but yet never completely over heated..

What is it, what do I do, please help, some one...

 

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Lets face it , you got a deal, with some possibly heavy baggage.

Something you might consider, get hold of a "Cooling system pressure tester" pump the pressure up to no more than 15psi , watch the gauge and see what it does.
If it starts dropping look for anyplace where you can see coolant leaking out. If external, you will see it and can make the necessary repairs if,however , the gauge goes down and you can't see any leaks that could mean it is leaking internally. Sometimes if it is leaking into the lubricating system , the oil will appear grey and soupy looking.
If it is leaking into one of the cyls , remove the spark plugs and look for heavy deposits on one of the plugs . If that is the case further testing will be required to confirm if it is a head gasket or something worse. The band aid you used sometimes works and sometimes doesn't. Only you know if the expense to remove the head(s) and confirm if they are OK will be worth it. Do you think that might be the reason you got ,"such a deal" ? Anyway, now you know what you might do.
Sounds like you like doing engine work and you just might enjoy tackling the job.