Hello I have a 78 250 Crew Cab, w/ 460 motor. It keeps getting hot up to 220* looking for more ideas to try.
We put AFR aluminium heads on it w/ new waterpump, headers, intake and the old 650 edelbrock carb.
It runs great, but tends to just keep climbing the temperature gauge. So we installed a new 4 core aluminum radiator with electric fan
and installed a 160* themostat. this held it at 180* for a little longer but if I get out on the highway it will continue to climb.
I took the hood off to try that and it didn't make any difference. I adjusted with the timing each way but it started pinging on acceleration, so
I put it back. Also run premium gas.

It's such a simple system! I thought maybe I could replace the waterpump again, altho it only has about 200 miles on it. I thought maybe we left out the backing plate but It
can see it between the gaskets. I got a new airfilter and fuel filter, just to rule out the simple stuff, might try some of that water wetter stuff, but it seems there is another underlying issue.
Any ideas or things to check?
Thanks

 

How old is the coolant? I'm assuming it's l new because you did the water pump and heads. Either way I'd buy a tester from an auto parts store and test your mixture.

If you take the radiator cap off, start the engine and let it warm up, do you see coolant moving when the thermostat opens? This will tell you if your system is severely plugged or if the pump is shot.

Could also get a digital temp gun and check the temps of your upper and lower radiator hoses and tanks. The lower ones should be cooler.

When you did your engine work, did you flush your cooking system out 100%?

Did it overheat before the engine work?

Could it be the thermostat is upside down?

Where do you have your mechanical gauge plumbed into?

 

Hello Dave,
Thanks for the reply, I can test coolant mixture, will try that.
No it wasn't overheating before but it was not the same motor either.
The thermostat was just exchanged for a cooler one, I had a shop do the radiator install, I could check also that while im in there.
Altho it acts normal in that respect, the gauge is plumbed in on top of the thermostat and i doesn't start to read until it opens at 160.
These AFR heads dont have any other spots to plumb in a temp gauge.

I do have a temp gun, and can check the radiator, but when it gets to 220* I will stop and let idle and nothing happens just stays there, so I will shut it
off (diesels sometimes) and let the electric fan cool the radiator, fire it up for a minute to let circulate and the temp immediately drops 10-15* I'll usually
do this a few times to get it cool then take off again. Lately it has been boiling the gas and vapor locking. I then have to put a little gas in the carb to get it
to pick up again. Complete Nightmare!!

 

Make sure both the mechanical and vacuum advance is functioning correctly. You mentioned advancing the initial timing till it pinged, but that isn't the whole story. Disconnect and plug the vacuum advance port and spool up the engine with a timing light and see that the timing moves smoothly to a total of 34° or 36° at around 3000 and moves quickly back down to base timing without sticking.

Then Re-connect the vacuum advance and also check to see that it adds more timing, in neutral with no load this might be 50° or more. Retarded ignition timing tends to runs very hot, not gonna say this is your problem here but it's important to eliminate all possibilities one by one.

Running a lower temperature thermostat will not really help with overheating, thermostats only set the lowest average temp the engine runs, not the highest, so if there's a defect somewhere it will still overheat. It will only slow it down by a few minutes. Generally it's best to run the factory spec thermostat. This was probably a 190° F. high flow or better.

WAG territory: Sure the electric fan isn't running backwards?

Have you flushed the engine well? Since it's getting hot on the highway, this points to something other than radiator or cooling system. Try opening the block drains and clearing with a coat hanger, a lot of rust sediment and scale have built up since 1978 I bet.

 

I know this isn't proper, but try taking the stat out and leaving it out and see if that stops the issue. Ran into this with my 390...it would overheat and actually spill out the overflow. Took the stat out and tried it that way and haven't had a problem since...have you tried boiling the stat to see if it opens? Today's new parts aren't very reliable and a stat could be junk right from the box. Just a thought to see if that will rule out a potential pump issue

 

Are the gaskets correct on the backing plate?. They are not the same.


pump to plate

plate to block

 

Thanks guys! this will give me some new stuff to try! Might take me awhile to get these Items checked off, but will re-post as soon as I find something!

 

Put the 160* t/stat in the bin and fit the 180* one back in.

Did you fit just one fan?

Did you fit a shroud with the fan(s) ?

Is the fan(s) powerful enough to work efficiently ?

Post up a picture if you can as a picture speaks a thousand words.

 

1973/74 with factory A/C and all 1975/79 trucks w/a 460 came with a Super Cooling radiator and a fan shroud as standard equipment.

If the shroud is missing, it will overheat.

 

Hi ND.

Yes, totally agree.

But !

The lack of a shroud should not be an issue at highway speed.

Just read the OP's 1st post again.

Is there any chance that the 460 head gaskets can be fitted incorrectly and thus block a coolant passage ?
(Something similar to the earlier water pump gasket post.)

 

OP is in Alaska where there aren't too many highways where one can speed.

In fact Juneau has no interstate highway, the only state capital without one.

To get to Juneau, you either have to fly in or take a boat.

 

Hi ND,

The OP seems to have found a highway.

 

My 74 highboy with 460 and stock radiator does not have a fan shroud. I live in Arizona... just drove to Phoenix last week in 105* weather... my truck doesn't overheat even while towing.

And there are lots of smooth roads and highways in Alaska...been on all of them.

 

Your 1974 F250 4WD was not available with a 460, so it was swapped in.

1983 was the first year the 460 was available w/a M/T & 4WD

 

What does that matter???He still has a 460 without a fan shroud and it runs cool.I have a 79 Bronco with a SWAPPED in BUILT 460 that doesn't have a fan shroud with the 351m radiator and it NEVER overheats weather I am in traffic or running wide open on the hiway.I still have the a stock clutch fan on it.The problem is the op is overheating and he is trying to find out why.Why should it matter weather other peoples trucks are stock or not???