'80 GM 350 4x 4sp 1 ton C&C. All stock. 40-60k on crate motor.

3 blade factory fan (good clutch- I think)

17" 3 core radiator (good condition)

new thermostat


Began heating 1 year ago only when climbing and over 16k gross. Now heating, open road, 10k, both into and out of head wind. Engine at stable operating temp when not at highway speeds.

Coolant clean. Fan clutch has resistance.

I pulled the waterpump- impeller in good condition and fixed to shaft.

I am thinking about upgrading to a 4 core, 19" radiator and a 7 blade fan. I picked up the fan, clutch and new 19" radiator mount from a salvage yard yesterday.

Now ready to purchase new 19" 4 core radiator. My only concern is that the truck was not heating until recently and that I may be covering up or ignoring another problem.

Comments / Suggestions?

Recommenations for good GM engine parts? Problems with recent Napa clutch pressure plates.

-Mike

 

What does the oil look like? Might be worthwhile to cut open the oil filter and look for metal particles. Has there been any noticeable difference in performance, fuel mileage? A lean condition and/or timing issue can cause heating problems. Just some thoughts, aside from radiator/ water passage blockage.-P.

 

The idea about a lean condition / timing issue was really good. I did not notice any change in fuel consumption- still drinks heavily. The timing has not be messed with and it is electronic- so it should not change... should it? Power / driveability remain unchanged. The truck continues to run and pull really well for what it is.

Oil looks excellent- recent change found nothing out of the ordinary- no particles at the plug - no metal. But your idea to check was really good. Nothing smells hot or seems odd- just the temp gague tipping past 240. When I pull over the radiator hoses feel really hot and the truck cools down quickly.

Would a slight deteriation in the fan clutch do it? I mean, could it still seem like it was working when in fact it was slipping a lot more than it should at high temps?

-Mike

 

Hmmmm. I guess the clutch could be the problem. Have you considered using electric fan(s)? They free up a few horsepower, and can improve your mpg too. Still, it's kind of a mystery why it would just start running hot all of a sudden, under certain conditions. I love a good mystery, but not when it comes to my vehicles...

 

Yeah, I thought about electric fans. Then I thought about complexity, cost, time and the fact that the factory system should work. Electric seems like a good idea for A/C and for BMW's and Corvettes where you only need extra airflow at idle. This thing needs all the air it can get when it is working. In order to do that, my alternator would have to carry lights, work lights, crane, truck electrics, AND cooling fans. With everything in place to run mechanical fan, and it bing an easy upgrade from a 3 blade to a 7 blade fan, that seemed cheapest (15$ salvage) and easist option. But I did think about electric fans either from salvage or from LMC truck. A 7 blade seemed easiest.

-Mike

 

I'd upgrade to the 7 blade fan, and get a new fan clutch. I don't know if you can do this with a 350, but if a fan clutch for a 454 will work, I would use that. The reason I bring this up is one of our plow trucks(Ford) has a 351 in it and it had a tendancy to overheat. Our mechanic we use when we don't have time to do our own work put a 460 fan clutch in the truck, and the problem is solved.

 

Thanks for the post Zane. I matched a 454 w/ AC specification fan with a clutch and radiator. I looked up the parts and then pulled everything I need from a scrap yard except for the radiator. Of course my new (junk yard) clutch may be bad as well- but I'll cross that bridge when I come to it. I'm only out $15 so far. I'll bolt it up when I get time next week.

The only question I have left is why the heating problem arose. I am beginning to think that it was a number of factors all at once- tired fan clutch, old radiator, low spec. radiator and fan- all conspired to gradually reduce the cooling capacity of a truck that is always over loaded.

-Mike

 

I think your on the right track with the fan. That fan clutch might not be engaging an running the fan at high enough speeds to cool the engine. Kind off a hard thing to diagnose when your driving the truck. Looks like your problem will be solved hopefully. Good Luck an keep us posted.

 

Thanks.

It is hard to spend much money on an old mule. But it has a Dana 60 front, a 14 bolt rear, a really solid, dry, strong non-oil using 350, a PTO winch, a crane and an excellent service body- so I hold on to the truck because it is a cheap tool for the money. And unlike the new trucks, you just don't worry about this one.

But it has to work when I need it and so I have to fix this new issue. Still, I can't really justify going to the GM dealer and replacing everything with new parts untill it stops heating. So I am stuck trying to fix it with out rebuilding something that may not be worth rebuilding. I figured the salvage yard was a good compromise for everything but the radiator.

I pulled the build sheet from the glove compartment this afternoon. On the second row, the sheet specs "Heavy Duty Radiator". But when I look up the radiator I have and all GM radiators used in CK trucks from '73-'97, the one I have is the smallest. I wonder what a non-"Heavy Duty" radiator would have looked like. Did they cover 1/2 of it with tape at the factory unless you checked the "Heavy Duty" option? Only fill it 1/2 full? Pour a tube of cault into it?

Anyhow- I'll bolt it back up after I pick up a new 19" 4 core radiator next week- the radiator specified for all 454s up to 79, only 454s with A/C to 81, only 454s with AutoTrans to 84, and only 454s with A/C AND AutoTrans to '87.

It's like in the 80's they kept cutting costs and making their trucks lighter until their truck was actually worse than their competitors' truck.

I'll post something about the temp issue when I am done. Problem is, because I have changed so much, it really won't tell us what the problem was. I will have either solved the problem, covered up the problem with more cooling capacity, or I have a different major issue and I simply threw time and money down a hole.

We'll see.

When I put the water pump cover back on and re-install the pump, would you guys recommend:

1) real gaskets
2) Form-A-Gasket, or
3) Real gaskets + Form-A-Gasket

And if I replace the one exg. manifold with a hair line crack, do you recommend the use manifold gaskets with the GM 350 or should they be installed bare?

-Mike

 

IMO I'd use real gaskets all around. Also, many of the gaskets they sell now-a-days for water pumps and t-stat's have a sticky side, need to peel off the slippery tape covering it before install. I'd also use the red RTV High Temp Silicone gasket maker on the water pump gasket, just don't overdue it. Finger tighten or loosely snug down, wait 15-20 min for it to form skin and torque in order and to spec and you're good to go.

 

I would try a clutch fan first.

 

Thanks-

Mike

 

The more I think about it, the more it seems like you are correct. But I have a tired radiator that appears to be the smallest one specified by GM- And so if I am looking at spending money to replace it and it only costs me an additional $15 in parts to fit the upgraded radiator, (larger shroud, fan, clutch and mounting bracket) I figured why not upgrade.

And I had a cooling issue even running loaded into very very strong head winds- a condition which suggests that airflow alone is not the single cause of the issue.


-Mike

 

If I were you I would get a lab thermometer or a candy thermometer and find out what the temperature really is for a start. It would be ironic to go through all this and find out that the temp sender was failing.

I agree with you on the air flow issue.

A three row radiator is not small. It should be very adequate. The thicker the radiator the lower it's overall efficiency becomes. If it is good, (did you have it flow tested?) and it was working for a long time before, it makes no sense that it needs to be "upgraded."

Are you losing coolant?

 

If it overheats on the freeway then the fan would not be the problem 50 mph + wind blowing through the grill is way more than any fan can pull. I would say you have a partialy cloged radiator unless the air flow through the radiator is obstructed. Also are you running a thermostat? Chevys can over heat without a thermostat to slow the flow through the engine. They need a thermostat or restrictor. Use gaskets for waterpump and if the exhaust manifold and head surfaces are good dont use any exhaust manifold gaskets they have a tendency to blow out in HD use.