The neverending OVERHEATING problem...please help!

My dad own a 1996 E-150 with the W351. The thermostat stuck a few months back and caused overheating, and without notifying me managed to damage a head gasket. A few buddies and myself decided to make this a project and do a complete rebuild.

Anyway we have the van back together completely now, solved a few minor leaks that we had and today have been a driving it a few days. With temps in the 40-50s, i didnt think overheating would be an issue. So over the last two days ive watched it go thru heat cycles, watching the temp gauge drop a little to show the thermostat opening ect. So today i decided to take it on the highway, and gradually over a few miles the temp gauge went up, and continued to until i got off the highway miles down with the gauge between the A-L of "NORMAL", so about 3/4 of the way.

Now i know this isnt overheating, but its definetly hotter than it ran before, and im thinking with more miles on the h-way, it would have kept going up. So i got off the highway, and it gradually cooled down and i noticed the heat cycles starting up again, and operating normal. Then back on the highway and same thing, temp back up. I got off the highway to head back to the shop i work at to check for leaks and on the way the temp dropped some, but not all the way back down at a little under half way. Then after parking and letting it run, the temp went back down to normal and is cycling back and forth now completely normally. I am totally stumped, and im praying to God this isnt another breach somewhere causing air in the system.

BTW-the heads were decked ect at machine shop, also we did complete bottom end rebuild. Also replaced water pump.

Any questions to assist in helping, please ask.

TIA
Dan

That was written a few days back, heres an update from today.

Scanner hook-up UPDATE:

So i brought the van up to work today to hook up the scanner and go for a run from there.

So i drove up to work thru traffic, about 5 miles and parked the van and let it run. It ran for about 5 minutes while i went and got the scanner, after hooking up it read 194-195 for temperature, perfect.

So i started moving and it slowly made its way up gradually to about 201-203 after a few miles, thats only expected. So now on a busy street for a lil bit before the highway and it made its way up to about 212-213. Got onto the highway and watched carefully.

After a minute or two it went to about 219, sat there for a mile or two and then started to flicker between 219-221, until finally stopping on 221 and spending the next few miles there. then flickering 223, then solid, then 225, solid, 227, solid. Oh boy. I decided i was going to get off and turn around, and see what happens. Right before i got off the highway it pegs 231 and im not happy. Current speed was at 67mph and timing was at 32 degrees according to the scanner.

So off the highway with the heat on, temp drops to about 226 and stays there till making my way back on the highway. With the heat full blast, i pulled the temp back down to about 219 in a relative hurry, it holds between 217-221 with the heat on. So at this point im eliminating getting air in the system (ie cracked head gasket, cracked head ect). So then i shut the heat off, temp goes back to about 226, then a mile or two, then 228 another mile and back to 230. Damnit, i decide to turn the heat on and watch it again. Within just a few miles, the temp now drops to about 215-217, which as far as i would think, would be normal without heat on.

I get off the highway with the temps at about 220, turn the heat on and help it cool. Now on regular street driving again it slowly creeps back up, not above 223, but higher than 212 like it did before. Heat on full charge, temps drop to 199 before parking it again, now this is weird: after parking and letting it run a few minutes it warmed back to about 210. So basically after a highway trip it wont keep itself cool at a stop like it did before.

Ok guys, i tried to explain that as well as possible. Please if u have any insight please help, im at a total loss here.

Any questions to help let me know please.

Dan

Did you use a factory thermostat, or an aftermarket one? If an aftermarket on, replace it with an OE, you will likely solve your problem.

The symptoms you post are COMPLETELY consistant with a thermostat that is not opening fully.

I work at a local shop and have for some time. My thoughts on the over heating wouldn't be thermo it would be fan clutch. It should not spin more then an inch or two if you spin it by hand with the moter cooled off.(over night) good luck.

Tha fan clutch adds nothing to the cooling ability at highway speeds. Put another way, a bad fan clutch will cause overheating at LOW speeds (stop-and-go, or at idle for example), not at highway speeds.

Tha fan clutch adds nothing to the cooling ability at highway speeds. Put another way, a bad fan clutch will cause overheating at LOW speeds (stop-and-go, or at idle for example), not at highway speeds.

Not to say you don't know what your talking about but that is incorrect.
The fan clutch is stiff at idel to move more air through the rad and air con to make both of these work to full potenchal. It is stiff cold(it idle) because the grease is cold. It then loosens up tell it hits a pre deturmend temp at this temp the spring winding on the front of it causes it to lock up agine......Like one of those old spring wound thermomiter.
So what your saying is only half true.
if you would like an example take a drive on a steep hill or over some hot road and you will here it turning its self on and off, the motor will roar or get a little loudder depending on how good your fan clutch is.

Tha fan clutch adds nothing to the cooling ability at highway speeds. Put another way, a bad fan clutch will cause overheating at LOW speeds (stop-and-go, or at idle for example), not at highway speeds.

This is what i was thinking also, but at this point, im willing to try anything.

I pulled the thermostat last night and boiled it, to me, it doesnt look like it opens completely, i have pictures on my computer and on a few sites, i cant get them on here tho. Try this link... http://nloc.net/forum/showthread.php?s=&threadid=107494

See if that works, if not, how open should the thermostat be? Does the side with the spring go all the way and seat so the copper piece is fully extended?

Dan