My dad has a 85 F-150 with a 302 efi and four speed 4x4. We rebuilt the motor two or three years ago it has .030 overbore and a rv cam flat top pistons. We have had overheatin problems with it for the past year now. Its usually only when we tow or when we drive up a canyon and work it a little. The first time it did it was last year when we were movin I have a single axle trailer with about 1500 ponds of stuff in it along with a full bed. I was goin up a slight incline at about 45 in 4th and it boiled over about halfway up the little hill(probly not more than 1 or 2% grade). The other time it started to over heat was when we had a 77 f150 on a trailer towin it back home it was on the free way this time, it didnt boil over but was startin to heat up got to about 210 or so, my dad was drivin(hes a truck driver so he knows how to pull heavy loads). When we got off the freeway and got down to about 45 it started gettin real close to boilin over till he put it in 3rd and wound er up to around 3000-3500. The last time it did it was yesterday he was takin a trailer home from my grandpas(60-70 miles) and he said it started doin it again. He has about give up on it and is ready to trade it to my cousin for his 75 2x4 with a 360. I used to have it and gave up on it when the rear end blew up. We dont know what to fix on it to get it to quit heatin up on us. Sorry for the long post thanks.

 

Well, there are many things that contribute to overheating, but one thing that definitely doesnt help is the .030 overbore. The less cylinder wall you have, the l;ess efficient the cooling system works. So, I would first make sure your stock setup is functioning properly. Give the rad a good flush with a garden hose in the top rad hole and let it drain out the bottom hole, then replace the coolant and flush out the block. also, make sure your thermostat isnt plugged or defective thereby blocking flow. However, if this doesn't help, you will need to invest in either a larger ford rad such as a four core unit or an aftermarket unit to overcome the overbore.

 

How much bigger is the four core in the 80s trucks. The one in there now is a little skinny bugger. I put a supercooler 4 core in the 76 but never messed with the one in that 85.

 

Had the same problem while towing (86F250 SC with 351) Turns out the fan clutch was the problem. Same small radiator.

 

Fan clutch got replaced with everything else when we rebuilt it. Could it go out in two years?

 

Well, and easy way to test it is line up one of the blades with some object and spin it by hand. the next blade shouldnt pass the object you lined the first blade up to by much. However, that would be more of a problem if you said it overheated in town or at slow speeds, since while your cruising, the truck moving is enough to provide airflow over the rad.

 

Well it does overheat at slow speed when we go up a canyon out here. Its steep and its dirt roads all the way to the top with very bad washboards so you have to drive in either second and bog it or granny low.

 

I bought a new fan clutch from one of the box stores 2 years ago for an '85 Oldsmobile. I had to replace it this past weekend after the car overheated in traffic.

It was a chinese junk fan clutch. Since it is under a lifetime warranty, they gave me a new one. Another Chinese junk clutch. Oh joy.

Bruce

 

210 degrees is not overheating. First thing I would do is put a real temperature Gage under the dash. See what temp it is really running. I would not worry about any temp till it gets at 230 and above.

If you find it boils over at a temp 230 or lower, then you might just need a radiator cap. You should have at least a 13lb cap on that truck, and it should be a recovery type cap and you should have the overflow reservoir hooked up too.

 

I know 210 isnt overheatin but its on its way and once it gets past that it moves alot quicker.I have put an aftermarket water temp volts and oil pressure gauge in it along with a tach. I have all the recovery stuff hooked up but not sure what the poundage on the cap is. It boils over above 230.

 

Did you try my method of testing the fan clutch? Also, another thing you should notice is after the engine is warmed up and idling, you should feel a good breeze behind the fan.

 

Well since it didn't start doing it till after a couple of years the first thing that comes to mind is the thermostat isn't opening all the way.

 

Boggerted I dont have the truck here with me its at my dads 60 miles away. I will be out there this weekend and we will see whats goin on with it. Also how could the thermostat not open all the way?

 

A thermostat failing is very common. They get gummed up and quit opening. Also make sure the bottom radiator hose isn't collapsing.

 

The lower radiator hose collapsing is a common problem with highway overheating. Some of the new lower radiator hoses don't come with the spring inside, so you have to pull the old spring out of the old lower radiator hose and re-use it. The waterpump can suck the lower hose shut at high rpm during highway use.