Overheating, tried (almost) everything.

[dagnabbitt]

This is a barn find I picked up a couple years ago, I have done the usual stuff that you do to a truck that sat for 15 years. New brakes all round, axle seals, new carb, plugs, wires, etc.

The truck is a hodge podge of what I imagine were spare parts. Its a 1981 with a pre-1976 stepside box, and a 1983-1984 front end. It seems like the interior is built the same way. When I got it it had a 1975 gauge package (or so), and nothing worked. I bought some NVU gauges, and thats when I found out I definitely had a cooling problem. The truck idles nice, and I can drive 40 mph all day long and itll stay at 180. When I take it on the highway though it climbs and climbs, it hit 250 today and I had to pull over.

So far I have:

- flushed the cooling system 3 times
- replaced the thermostat with a 165F
- replaced the rad cap
- moved the temp sensor from the head to the intake and back again.
- changed the oil, set the timing, and all the other stuff that can make a 5 degree difference.
- Although a new rad cap should eliminate the problem I still checked the hoses and none of them are collapsing under revs.


Am I avoiding the obvious... that I just need a new rad, or is there something I am missing?

Thanks all.

[geezer#99]

Hoses won’t collapse if you sit there and rev it. Gotten get it real hot and look at them. Especially the bottom one.
You might need a coil. Easy to make and install one.
You could try putting an air dam under the rad cradle to help air flow thru the rad.
What’s your timing set at?

[Greenlee]

My guess is your radiator is clogged up. Mine did this, mostly if I put a load on it like when pulling a trailer. I kept flushing the radiator and thought the radiator looked fine. Finally, I replaced the radiator and now it almost seems like it runs too cool. I can pull a trailer or do just about anything with it and the temp hardly rises.

[Dead Parrot]

Verify the temp with a laser temp reader or a second temp gauge. Your gauge reading of 250 seems out of bounds as 50/50 antifreeze mix boils at about 234F. Even a new gauge can be bad out of the box.

Didn't see any mention of a new water pump. Possible the impeller suffered some corrosion during the 15yr sit.

What does the flow through the radiator look like with the cap off?

If the heater return is to the radiator, how is it flowing?

Was the air out of the heater hot with the fan on high?

BTW - for a mix-master truck, it looks pretty nice.

[Bandit130]

If it still has original radiator, then it is possibly clogged, or partially. My 75 had original radiator and thought was cooling normally till I had AC redone in 2016. Technician found coolant was chugging (so to speak) through the upper radiator hose. I could see it and tell. Not many places will re-core anymore due to the age. Had to replace radiator. Another possibility is fan, clutch, shroud, etc. All these can cause issue. Fan blade should be half blade width in, half out. This I found out from many sources. Hope you find the problem.

[nonstop]

Another thing to consider is your thermostat. Especially on the highway, the coolant is not being kept in the radiator long enough. You might consider at least a 180.

[dagnabbitt]

Originally Posted by geezer#99

Hoses won’t collapse if you sit there and rev it. Gotten get it real hot and look at them. Especially the bottom one.
You might need a coil. Easy to make and install one.
You could try putting an air dam under the rad cradle to help air flow thru the rad.
What’s your timing set at?

The bottom one has a spring in it, I know that one is not the problem. The top hose is pretty soft and I am not sure its the right application. But I don't think its the hoses, I've certainly seen worse.

[dagnabbitt]

Originally Posted by Dead Parrot

Verify the temp with a laser temp reader or a second temp gauge. Your gauge reading of 250 seems out of bounds as 50/50 antifreeze mix boils at about 234F. Even a new gauge can be bad out of the box.

Didn't see any mention of a new water pump. Possible the impeller suffered some corrosion during the 15yr sit.

What does the flow through the radiator look like with the cap off?

If the heater return is to the radiator, how is it flowing?

Was the air out of the heater hot with the fan on high?

BTW - for a mix-master truck, it looks pretty nice.

When I pulled over you could hear it boiling in the top hose, its pretty hot. I have verified the temp with laser.

The air out of the heater was very hot, with fan on high.

With the cap off, engine warm, you can see nice flow through the rad. That's why I was hesitant from the start to replace it. But I am down to just a couple more possibilities here.

I will check the heater return to the radiator. All hoses are very hot, though, so I believe that the flow is there.

And thanks, its a bit of a head turner, I have a few other project trucks but it is my hope that this one be my daily driver, so I am anxious to maximize my summer driving time with it.

[mMad Dawg]

Do you have a fan shroud. If you don't the is probably not being drawn through the rad.

[mMad Dawg]

Sorry I meant the AIR is probably not being drawn the rad.

[tucsonjwt]

Same thing happened to me. Classic sign of needing a new radiator. This is one case where I think the cheap Spectra brand is a good choice. Look for 20% off sale at Autozone with free shipping that they sometimes have, or just google the part number for your truck. Mine was less than $100 including the brass/copper scrap radiator I had. (cut the brass tanks and core away from the steel mounting parts for more scrap value.)

[dagnabbitt]

Originally Posted by mMad Dawg

Sorry I meant the AIR is probably not being drawn the rad.

Thanks, I should have mentioned this because its important: I do have a fan shroud.

[dagnabbitt]

Originally Posted by tucsonjwt

Same thing happened to me. Classic sign of needing a new radiator. This is one case where I think the cheap Spectra brand is a good choice. Look for 20% off sale at Autozone with free shipping that they sometimes have, or just google the part number for your truck. Mine was less than $100 including the brass/copper scrap radiator I had. (cut the brass tanks and core away from the steel mounting parts for more scrap value.)

Yeah in Canadian funds I have found a couple at around $170 delivered, which is pretty good for us up here.

I'm thinking I need a new one based upon some of the feedback I have received here.

[3drburb]

Maybe drill 2 very small holes on opposite sides of your thermostat install it then with your radiator full start the truck without the cap on and let it run for a while, if it burps any coolant out replace that and put the cap back on and test it out.
It's most likely trapped air because it doesn't do it sooner.
Btw I had this problem and did this to my 425 Olds about 15 years ago and never had a problem since.
Good luck, overheating can keep you on edge and drive you nuts.

[Dead Parrot]

Since you have access to a laser temp reader, put your 180-195 thermostat back in and do the 40mph drive to get it to normal operating temps, preferably on a cooler day or morning. Once it is normally hot, take several readings from many different spots on the radiator. If you find a lot of cool spots, probably places where the water isn't flowing. Even better would be if you could use a night scope.

Couple more questions, type and number of blades on your fan?

Does it have a fan clutch? (fan clutch + flex blade fan = poor air flow)

You mentioned flushing the radiator, have you made sure the air flow passages aren't full of 15yrs of dust and barn fluff?

[burkeftm]

Another thing to check is the heat riser in the r exhaust manifold ,from sitting so long it may be seized restricting the exhaust( this is if it has the original exhaust set up won’t apply if headers were installed) I had a small block manny years ago that was overheating because of this. Just something simple to check ,also as another member stated ,check for debris/dirt in rad fins,nice looking ride Bob

[tucsonjwt]

z2 on the fan clutch. I would only buy AC Delco on the fan though. A proper shroud is also critical

[3drburb]

Also check or replace your belts and make sure they are tight and not slipping at higher speed.

[Wgesnerjr]

If this is a "hodge podge" of parts. Consider the fan and water pump. They might be one from a serpentine set up. Those have a reverse rotation water pump and fan.

[v30crewcab]

easy to check a clogged radiator. it will be hot to touch on the top, and colder down lower where its clogged.

[Nick_R_23]

I had a truck years ago that had a cooling issue similar to that. At idle, or low speeds, the truck had no problems, but at highway speeds it overheated quickly. Cooling system was in excellent shape. I noticed one time as I was trying to diagnose things, that I was feeling air being pushed forward instead of being sucked into the engine bay through the radiator. I inspected the fan, and sure enough someone had installed a fan with blades facing the opposite way. Being that there was still air flowing over the radiator, it cooled it just fine until you ran into oncoming air at highway speeds, and with two opposing air forces it just created a dead zone right at the radiator. The correct fan solved the problem.

[dagnabbitt]

Hey guys I really appreciate the feedback and suggestions. I have checked my clutch fan and everything else, but finally I took the advice of several people who posted, removed the radiator and shined a shop light in it to get a good look at it. It looks like despite my efforts at flushing the system that it is likely clogged.

After toying seriously with the idea of submersing it in pure CLR (but searching the forums and learning that was probably a bad idea), I figured that I needed either a replacement or a recore.

I was just about to pull the trigger on buying some online whatever for about $600 Canadian (shipping, exchange rate), when I found a shop that would not only recore it, but would turn it from a 2 core to a 3 core for about half that.

I am hoping to get it back next week and be driving again. I will keep you posted.

[dagnabbitt]

Just to circle back: I had the old rad recored and replaced the fan with a seven-blader for good measure. Runs so good now.

[Pontiac1976]

Glad to here it's good now.
What a did the re-core cost for the 3core out that way.
Last time I got my 73-80 3core 12 yr. ago it was about $240.

[dagnabbitt]

Originally Posted by Pontiac1976

Glad to here it's good now.
What a did the re-core cost for the 3core out that way.
Last time I got my 73-80 3core 12 yr. ago it was about $240.

I paid more than $300: they added restrictors to make it the equivalent of a four-core, which was probably overkill but I was sick of overheating. Despite the expense I was very happy with the job they did. A new 3-4 core delivered in Canadian dollars would have been more money and then who knows if it fits properly.

Yesterday it was 34*C and I was on the highway doing 80 mph, temp gauge never went higher than 175.