Truck overheating under load.

[LD1]

What was not mentioned in the original post is at what speed is he moving? If it's a real hard climb at slower speeds, yes he needs the help of the fan and shroud. No doubt about it. As to highway speeds, I think any help would be pretty marginal.

The problem with the non-clutch idea is that an OEM application is not available. When the 5, 6 and 7 bladed fans came out, they were with a clutch assembly, and the fans won't bolt to the water pump hub. There are a few small 5 bladed units around. There are also some 6 bladed aftermarket flex-fans, but they are more show than go. The best is to have an OEM 7 bladed on a clutch.

Yea, I am not sure what compatability issues therre might be.

But the block is still the same. It would probabally be possible to get a waterpump for an older 350 that did not use a clutch. It should bolt right on the block and give the correct hub/bolt pattern to use a rigid fan (also from earlier 350)

 

[bigtiller]

I had one that was built in '88. The water pump on it did leak but it was slow enough that it seldom left a spot on the floor. It got to a point where I was having to add coolant every 1000 miles or so - ( once a month ) - . I put 3 pumps in that truck before I sold it with 118,000 miles on it.

 

[75H2]

Plugged cat?

 

[hrcarver]

Plugged cat?

I think with all these replies, I should be able to pin it down this weekend, but I didn't follow that one, cat converter?

 

[PoorMansCat]

Only overheats under hard load...
I WOULD suggest that you check temp. differential across the cooler, it would be THE most reliable way of determining where the issue lies.. but that may be hard to do on a piece of mobile equipment, so...
If the truck is equipped with any other coolers that are in front of the radiator (i e a/c condensor, trans. cooler, p/s cooler) then verify that there is NOT a build up of road grime between the coolers that is restricting air flow.
By using compressed air with the engine off and holding your hand on the inside at the same time, you can determine whether or not the cooler is restricted on the air side. If no compressed air is readily available, use a GOOD flashlight and a friend to shine the light thru from one side while you follow the light from the other.... YOu SHOULD see light everywhere, if light does not come thru, then neither can air..
Make sure you ahve a thermostat installed, without it, the coolant wont stay in a properly functioning radiator long enough to strip heat out of the coolant. (when working hard)
Yes, pump impellers can erode away, usually its due to poor cooling system maintenance.
As 75H2 stated, a partially plugged exhaust system will cause the engine to run hot. It wil be exponentially worse as heat, load, and engine speed are increased. Another possible issue could be engine timing. Can't remember which specific years, but if you have the flyweights and springs inside your particular year of distributor, if those wear out or the springs break, the engine timing will NOT be correct for engine speed/load.

 

[timswi]

If that were to plug up, the truck would quit running in a few days or run very poorly.

True, a clogged cat is a short term problem, as is a stuck thermostat...My first check would be the condition of the cooling system. If the antifreeze has never been changed, this could cause restricted flow that may only show up at times of abuse.

I had a 91 & 97 5.7 and they never ran hot. Was towing a 32 ft travel trailer with 175,000 on the clock with the 97 and it never complained.

I would not put a 160 thermostat in that truck. They are designed to run on a 195 and the performance will suffer.

Is the rad original or may it have been replaced with a budget or 6 cyl light duty version at some time?

When this overheat happens, do you lose heat from the HVAC? I'd also check that. Sometimes that will tell you if the cooling system is "stalled'.

The clutch fan could be bad, but I also think this would show up in non towing situations unless high RPMs and a heavy load are causing the clutch to go to idle due to a bad clutch. Never personally experienced that. Summit Racing does sell a variety of non-clutch high volume racing fans. I've used these on big-block Chevy cars with much success.

 

[Mace Canute]

A rad cap that has lost some of it's pressure rating or isn't seating absolutely right on the radiator neck can also cause an over heating problem and a lower rad hose can collapse and restrict coolant flow because the internal coil spring corrodes away over time. I've seen grunge from coolant that should have been changed a long time previously cause a rad cap to not seal properly and cause an overheating problem.

I believe the problem is airflow related and that the rad and/or AC condenser needs all the bugs and dirt and stuff cleaned out from between the fins. That would be the first thing I would make sure was correct. The second thing is probably the rad cores have become restricted by grunge building up inside the tubes over the years and need cleaning out at a rad shop or maybe a new rad is more cost effective. You can get an idea of how much there is yourself by removing enough coolant to be able to see the end tips of the tubes. (FWIW, I've owned Chevys with 350s in them for decades and have never seen a bad pump impeller in any of them....bad seals, yes but never a bad impeller.) It might be a bad thermostat and if you decide to replace it, use the same temperature rating as the factory calls for.