Checking to see if you guys can help out. I've got a friend with a '94 F-150 with a 4.9L and 5 speed. It is a chronic overheater. To date, he's changed the Thermostat, Radiator, Water pump, fan clutch, and flushed the block. It's got a weepy head gasket (about half a gallon every month). He doesn't want to change it untill he finds the problem, because he's afraid it'll blow the new one too. It runs on the high side of normal around town, and gets to 260 deg. on the highway. I'm baffled, because my 96 runs super cool, and I have to partially block the radiator in the winter to get it to stay warm when the thermostat cycles. Any thoughts?

 

Is it the original head gasket? It might have just blown do to age and not a problem with the cooling system especially since everything is new. The only other thing I can think that would cause overheating is timing, not everyone knows that but incorrect timing can cause overheating.

 

A good point, but I forgot to mention that we did check base timing timing too and it was right on the money. Suspecting a spun balancer, we tried 5 degrees advanced and retarded to see if this would help the condition, but it made no difference. The truck runs like a bear and has great pickup and response. Yes it is the original head gasket. Like I said, I'm baffled on this. If anything, my truck overcools, so I am at a loss.

 

As a general rule of thumb, both the 240 and the 300 Sixes, as you posted about YOURS, run quite cool. With the host of parts you have replaced, with the tests you have done, and with the flushing you have done, another alternative to a head gasket blown between a cylinder and a water passage is a LOWER radiator hose that collapses as the engine speeds up. It can--and does--happen; the lower hose may have age in it and it kinks until it eventually practically closes up as the engine speeds up and the engine heats up due to the restrictive flow.

Since the truck is a 5-speed, obviously, an automatic transmission can't be overheating its fluid and that winding up overheating the coolant in the radiator.

It is, of course, POSSIBLE that the new thermostat is defective or the water pump is defective. A defective pump is somewhat rare, but I have seen them right out of the box and the impeller is so loose on the hub shaft that one could hold the hub in one hand and spin the impeller as freely as could be. Obviously, that pump did NO pumping at all.

Finally, is the belt routed properly around the pump pulley?? If it is NOT routed properly, the pump impeller will be spun in the wrong direction and it will NOT pump water. If the belt is routed properly, make sure the pump part number your friend purchased matches what the 1994 engine should have!! It is possible the counterman at the parts store accidentally got the wrong pump.
Truly, I hate to ask this question; still, I have seen it done before: Did your friend install the thermostat with the temperature-sensing "pellet" facing the ENGINE?? If he installed it backwards, of course, it won't operate correctly. I have seen that mistake happen several times. I am NOT trying to be critical; rather, I am merely trying to think of all the possibilities.
I really do these thoughts will help you out!

Please post what you all figure out and how you rectified the problem.

 

I don't take it as critical at all, and I appreciate the thought you guys are putting into this. The hoses are new (but that doesn't mean they can't be sucking shut). We'll have to check the water pump for impeller tightness. I'll keep you posted, and once again, don't worry about being critical. You guys have an outside perspective and can point out things that we might not see being so close to the situation. I think it's unlikely, but we'll check the thermostat too. The belt is routed correctly, though.

Thanks again, I'll let you know what we turn up.

 

Here's my 2 cents.
I'd like confirmation that the temp reading on the gauge is anywhere near correct.
A quick and dirty first pass would be at 260 degrees you wouldn't be able to even touch the upper hose. If it were running at 200 or so, you could count to two full seconds before you had to release.
Look into that. Good luck.
Steve