While dropping my stuff at school today the truck started smoking and dumping coolant out the over flow hose. The temp gauge or sensor does not work and was on my list of things to fix, the truck seemed to be running slightly hot lately, but we've had it loaded up with about 700 lbs and drove it farther than today and it did fine. Any ideas on what the problem is?

The tuck is an 85 F150 4*4 4spd with a 300 and all the usual bolt ons.

Thanks,
Sean

 

It got hot. There could be several reasons. You could have a small leak and the coolant just kept getting lower and lower and running hotter and hotter (which you couldn't monitor without a temp guage) untill it blew like ol' faithful. You could have a thermostat that stuck. You could have blown a head gasket. If the cause was 1 or 2 you may have a blown head gasket now. If it blows coolant out of the radiator while running before it gets hot-it does. Refill the radiator and run it with the cap off and make sure it has good circulation after the thermostat opens (if it opens) . Another problem could be a clogged up heater core or radiator. Bubbles in the coolant or coolant in the oil means a tear down. If the flow seams slow, (it should run like a river), flush the system (you can get a kit from your local auto supply with all the directions if you don't know what to do). Finally, if you are lucky enough that no major damage was done to this motor, DO NOT PASS GO... do not run this vehicle untill you trace the problem with the temp. gauge. It is probably a loose wire-(free) a sending unit, or the guage itself, none of which cost squat compared to a rebuild.

 

Double post and I can't figure out how to delete.

 

Does it only overheat when going very slow or stopped? Could be your fan clutch or could be the thermostat.

EDIT: Well, there's a more detailed answer above, I've just had this page open, waiting in line on Firefox, lol.

 

So it seems as though replacing the thermostat it what I should do first? I am almost positive there isn't a small leak unless its small enough that it wouldn't leak unless the truck was running. I was under the impression that thermostats usually got stuck open so it would run very cool if the thermostat was bad, which is why I didn't replace it when the truck seemed to be running hot.

 

My 80 will leak so slow and slight that you can't tell it. When it gets to the point the that there is not enough coolant to keep up, it overheats, the radiator turns into a pincushion with lots of very small pinhole leaks. Up to that point, it runs fine and as soon as it gets refilled and cooled down, the pressure drops and the leaks dissappear, but obviously they are letting minute amounts of coolant escape. There is a special thermostat on the market designed to stick open if it fails- all others stick closed. Do yourself a favor- when you replace that thermostat, take the old one, (and the new one ,as far as that goes), and put them in a pot of water on the stove and monitor the temp. at which they open. This will erase all doubt as to whether that was or will be a problem. Make sure that you install the thermostat facing the right direction. It goes without saying , that you should keep a close eye on the coolant level for the next few weeks.

 

I've owned 2 Ford trucks with the I6 engine. It's a darned good engine if you're not doing heavy duty work. The 1st one was a '78 F-150 with the 3-spd. + OD manual trans. The current one is an '84 F250 4WD with T18 4-spd. Both of these trucks ran warm in the summer and when hauling.

The '78 needed a new radiator, so I took it to a shop to see what they could do. Turned out that they had no 300 type rads so tossed in a 351 type for the same price. The new rad was a little bigger than the old one but there was plenty of room for it, so no problem. That was either a good deal or they were getting a little extra from the 300 rads. Either way, the new rad cooled that 300 perfectly. Even in stop and go city driving on a 100+ degree day it never over-heated again.

I'm considering doing the same thing for my '84. It has AC and heats up on hot days when the AC is used. The temp needle gets up to the "A" in Normal, where it usually runs in the N-O area. Seems to me that the stock 300 rads are marginal at best and an upgrade to more cooling capacity seems a good idea.

Ed

 

I'd still suspect the fan clutch. Dont just start throwing $$ at the problem. First, get your gauge working!

The sender is under the intake manifold on the passenger side of the truck at the back of the head. Single wire connects to it. If you ground the wire to the frame, the gauge will swing all the way to hot. If that happens, replace the sender. Its cheap.

 

It was good enough advice to be posted twice.