Overheating '78 F150

[shortbed]

My 4 wheel ‘78 F150 straight 6 started overheating last summer. It was alright around town, but on the highway it would take about 15 minutes and she’d start boiling.
I replaced the thermostat first thing, not it, then finally was able to get the right radiator and replaced that, which seemed to fix the problem. Last weekend I drove across the state (Roanoke to Richmond) and had no problems, but on the way back (the next day) it started up again until I could only drive on the highway for ten minutes or so before it would overheat.
Recalling last summer, I waited until dark and was able to limp home. The highway speeds and summer daytime heat is what it takes to overheat it.
When I got home I replaced the water pump and the thermostat (I ran it without a thermostat to get home), and filled with the proper mix of coolant but it still overheats during the day at highway speeds.
There is no water on the dip stick. There does not seem to be anything different with the exhaust. And she runs great otherwise.
Does anyone have any ideas . . . ?

 

[blacksnapon]

If your timing is ok, and it starts all right, I'd take a look at the fan clutch.

 

[Mil1ion]

How are you determining it is overheating ?

Temp gauge ? .. Don't go by the temp gauge they are prone to read wrong

Blowing fluid out ?.... are you overfilling the radiator ? people do it all the time.

The proper level is 1" below the sealing ring of the rad cap....no higher.

 

[flathead95hp]

Check the radiator cap, I had the same problem, turns out the seal was split and only did it on the highway. Also may want to check to see if one of the radiator hoses are collapsing on themselves. Hope it helps.

 

[shortbed]

Thank you guys, for the replies, but
1 -- there is no fan clutch
2 -- I’ve changed out the cap (tried it loose, tired it with a 7 pound cap and 13 pound cap. I don‘t think that’s it
3 -- I’m not overfilling the radiator
4 -- hoses are not collapsing
5 --And believe me I’m not going by the gauge alone, which, though it’s very accurate, would not account for spewing green liquid when I loosen the cap.

This truck is a great, I mean great, truck. It starts like a dream on the coldest days, runs terrific, has few problems, for the most part, and . . . most importantly for me . . . is a working truck. I depend on it. I'm a carpenter and use it every day. So, besides loving it, I NEED it.
Any other ideas of what I could do to figure this thing out ?

 

[flareside_thunder]

does it still have the fan shroud?

 

[bucks77ford]

does it still have the fan shroud?

I was also wondering that. How far is the fan away from the radiator?

I would get a manual gauge and see what exactly the temp is.

 

[flareside_thunder]

I had a 78 that kept overheating cause it didn't have a fan shroud......I had to get a junkyard one and that fixed it.

 

[Mil1ion]

ok i'm curious about what level the coolant is filled at.

btw, you don't remove the cap until it is cool

 

[bucks77ford]

ok i'm curious about what level the coolant is filled at.

btw, you don't remove the cap until it is cool

Dangerous to do so too.

 

[shortbed]

Well, okay, there is no fan shroud. When I was limping home the other day I talked to everyone who worked in a parts store along the way, and everyone who owned an old Ford truck and everyone who looked like they might have owned an old Ford truck or knew someone who did . . . and the fan shroud did come up once or twice. Thing is I’ve owned this truck for ten years and it ran fine without one all that time.
One of the other things I was thinking is that the last radiator might have gotten clogged with engine rust or debris. The truck did sit without much use for a couple of years and I thought maybe this one could have gotten clogged too. I did drain and rinse out the hoses and what I could of the engine when I replaced the radiator the first time and the water looked fairly clean, but . . . . Now I’m thinking the only other thing to do is replace the radiator again . . . What else can I do . . . Oh and ‘MiL1ion’ about not taking off the cap when the coolant is hot . . . I found myself impatient. I’d been driving all day and wanted to get home and the truck was overheating every half hour, so I would stop, wait and then turn the ignition key on to see just how hot the radiator was and when it would get down to about midway on my gauge I’d crack the cap and let the pressure off a bit. My worry was not about my safety. I was pretty careful, my worry was about putting even lukewarm water into a hot radiator and still wonder if that couldn’t have done some damage.
But anyway, the radiator is now the only thing I can think of to be changed. If anyone has any other ideas, I’m all ears.

 

[flareside_thunder]

yea I was ansy 2 weeks ago and kinda ticked at my Fiance's dodge....started spewin coolant all over the place went n bought a new one and replaced it in the parkinglot of the parts store...burned my right arm up past my elbow, got my left hand and in the face...i wasn't thinking but I can tell you I was cussin up a storm....so be careful.I know you said you just replaced the thermostat...what temp stat did you replace it with? It's possible you got a defective one right off the shelf....I've had that happen more times than I'd care to count. Just to rule that out check the temperature and post it up...if it seems right to us on here then I'd suggest pulling it out and test it in a pan of boiling water on the stove...all you need is the stat the boiling water and a thermometer....

 

[shortbed]

Hey, flareside_thunder, I don’t doubt parts can be defective right out of the box. I had one of the national parts chains sell me a defective or incorrect starter solenoid two times in a row a few months back. And, boy I’ll bet you were . . . I keep wanting to say, ‘hot’ or ‘burned up’ about that coolant, except I know how scary and dangerous those volcanic radiator eruptions are and I’m glad to hear you weren’t hurt any worse than you were.
I did try several things with the thermostat: I had been running a 180 degree thermostat and when all this started I tried running without any thermostat at all . . . and then I tried running it with a 160 degree thermostat. Neither of those choices changed anything. The book calls for a 190 or maybe its 192 degree thermostat. When I put the 160 in, my gauge showed the temp. exactly where it should be if the gauge was working (just a bit to the left of where my 180lb had read)
My gut tells me there is something else going on, and I can’t help but feel its something simple that I’ve overlooked, at least I hope so.
Thanks again for your help. I’m going to check back after church.

 

[Blue Goose]

You might look for some "tattle tale strips" to put on the radiator tanks. My neighbor is a mechanic for a Caterpillar dealer and when we were having similar issues with my parents motorhome, he stuck some temperature "tattle tale strips" (that's what he called them) on the tanks of the radiator. Those told the temperature drop from one end of the radiator to the other and helped determine if the radiator was doing it's job.

 

[bucks77ford]

You have already made changes to your thermostat and radiator. I'd have to be a pretty unlucky coincidence for both to be defective, but it does happen. I would get a fan shroud. That would help out some anyway. The other thing that I'd probably do is to change out the temp sending unit, unless you've done that already. This way you can be sure the gauge is reading correctly. It still would help to get a manual gauge to see exactly where your engine is running, but if you do get a gauge, make sure you do change the sending unit just to be sure. You'd hate to spend the cash getting a new radiator when something simple could be the problem.

 

[Mil1ion]

one must remember the t-stat is merely a switch.
it should be wide open at its designated temp value. they rarely close at hotter temps.

these engines run at 208-210"*F your 160 t-stat means nothing as far as the gauge goes at normal operating temp.

I would be putting a candy thermometer in the rad cap opening to get a good idea of normal coolant temp at idle.

Is the engine timing correct ?

Absolutely make sure the coolant level is 1 - 1 1/2" below the lower sealing ring of the rad cap opening.

any higher will cause coolant blow out

 

[flareside_thunder]

I completely understand man and something else is bothering me about this.....You said you'd already replaced the water pump. However, it'd put my mind at ease if you would pull the radiator cap off and make sure the coolant is actually flowing when at operating temp....

 

[shortbed]

Hey BlueGoose, I like the idea of the tattle tale strips. I’ve tried something like that before by putting my hand on the front of the radiator . . . Feeling around to see if the coolant was circulating evenly or if one area was cool. With my last radiator I found that, in fact, there were cool areas and that was one of the reasons I replaced it. I will try that again with this new one and see if I can’t find irregular temperature ranges on the fins.
And Bucks77Ford, I don’t usually trust gauges, but this one is right on the money every time, still that is one of the reasons I’ve cracked that cap when it was still hot, just to make sure, and gentlemen, I can assure you, my truck is overheating.
And MiL1on, like I’ve mentioned, I’ve run the truck without the thermostat . . . That is NO thermostat at all and it STILL overheats. If the thermostat was causing my truck to overheat, don’t you think removing it and not having a thermostat at all would rule out the thermostat as the cause of the problem?

As far as the engine timing. A friend, who knows how to check timing, and I did check it about two months ago. It was reading just a bit off exact. I forget if it was advanced or back a bit from right on, but it was not fussed with then or since and the truck runs exactly like it always has, except for this overheating thing. If the timing was the problem, would the truck be sounding or running badly? I’ve never done much with timing, all I recall about timing is watching old timey mechanics time a vehicle by sound, turning the distributor and tightening it down when the engine sounded . . . Sweet. My truck, as everyone who has ever listened to it will testify, has always and still, sounds sweet. She’s just got something on her mind these days. Something, guys, seems to be troubling her and she gets fit to be tied and then blows her stack every time she thinks about it.
Well, kidding aside, right now this is where I’m at:
Check the radiator for uneven cooling (thanks bluegoose)
And make sure, make absolutely sure, that the coolant is absolutely not higher or lower then one and one half inches below the lower sealing ring of the radiator cap opening (I want Mil1ion to be able to sleep tonight).
I'm going to keep on checking back here to see if there are any new ideas and keep you guys posted about my progress.
And, by the way, thanks for all the suggestions.

 

[flareside_thunder]

the only other thing I can think of would be a gasket leak...either intake or headgasket.....my truck ran like a top with a headgasket leak but overheated and overheated..sho nuff that's what is was......

 

[shortbed]

Hey, flareside_thunder. that's also a good suggestion. I did that with the other pump and I could see the coolant flowing. I replaced it anyway because I thought that the pump might be working only intermittantly, you know slipping on the shaft, when I took it out it seemed right as rain, but I replaced it anyway. But I will do that again, first chance I get and see if the coolant is moving. Good idea. . .