Truck overheating under load.

[hrcarver]

My old one ton(1989 chevy, gas 5.7L) is overheating(near the red on long hills) under load on a pretty regular basis. I do not recall it having this trouble before this year. Do water pumps go bad before leaking? Anything else it could be besides the thermostat?

 

[Thomas]

Maybe good rad. flushing plus outside rinsing also thermostat first.

 

[Diamondpilot]

As cheap as it is for your truck I would put a new water pump on it anyway. The real reason is your radiator. It needs professional acid cleaning or simply replace it. My dads Corvette was doing the same thing and I found a new old stock rad for $160 on the net.

Why I say to go ahead and replace the pump is you might as well while you have the Rad out. These old 5.7L motors are so cheap to work on. I would guess its less than $40.

So go shopping. Get a pump, T-stat, and a Rad.

Chris

 

[chips papaw]

well have you checked for any leaks.that would be the first thing.if you have to keep refilling rad its going somewhere pull the dip stick look for water in the oil this could be a sign of bad head gasket if not check the freeze out plugs they can look good on outside but they rust out from the inside they can just seep untill under pressure. if your truck has a lot of miles on it check raditor hoses they can cause same problem this truck should have a plastic jug for over flow from raditor they will crack on the bottom with age.heres something else if the truck has been driven a lot at night the cooling fins on raditor can be pluged up with dead bugs keeping it from running cool because the air flow is restricked.also check carpet under heater core see it it is wet that is a sign that a heater core could be leaking. these are things that can cause your problem that can be check without costing you money while trying to find the cause of your problem

 

[zzvyb6]

Do the easy things first. Pull the thermostat and see if the problem goes away. If there is a fan slip clutch, make sure its engaging when it warms up.

Look into the radiator opening and see if there is fluid flowing when the motor is running. Drain the radiator and see what comes out and how much. If you are loosing fluid, see if its a leak or its being burned. Look into the tailpipe and see if there is antifreeze residue at the end. Do you have a burp bottle? If it has a leak of its own, the fluid's just being pumped out. Fan belt tight? Manifold gasket any good?

 

[zene55]

Several things to check.

1. Level in the radiator before and after event
2. Fan belt - may be slipping - poor air circualtion and poor water circualtion
3. Water condition in radiator - if dirty flush it.
4. Oil in engine - does it have any water contiamination - may have head gasket leak.

 

[LD1]

I had a similar problem with my 03 chevy.

It was the fan clutch.

What type of fan do you have?? It could possibly be one of 3 types. Either a flex fan(fiberglass blades), it could be a rigid fan bolted directly to the pully with steel blades, or it could have the clutch. It is an aluminum looking housing that the fan bolts to and IT bolts to the pully. It's about 8" in diameter and has several "fins". This is the type I am talking about. If it is either a rigid or a flex fan, there isnt a lot to go wrong.

But the clutch fans are filled with a viscous fluid and they also have a bi-metallic spring. They are supposed to turn hard when cold, then get easier to turn, and then get more difficult as temps get even hotter. If one fails, the fan will still spin when the motor is running, just not as fast as it should. When you encounter an overheating event, pull over and shut the engine off and try to see how easy the fan will turn. If it has a decient amount of resistance, you are okay, but if it turns easy, it is probabally the problem.

Aside from that, if it is due for a usual service, it wouldn't hurt to change the coolant/flush the system, and maybe spend $5 and put a 160 degree t-stat in it. But chaning the pump and radiator and removing the t-stat ISNT going to help if the clutch is failing.

 

[LD1]

I just checked autozone and they do offer 3 fan clutches. A standard duty which is used without AC, A heavy duty which is used with AC and a higher rear end ratio, and a sever duty which is used with AC and lower rear end gears.


http://www.autozone.com/autozone/parts/1989-Chevrolet-K3500-1-ton-P-U-4WD/Fan-Clutch/_/N-ih5ohZ9pd92

So if your truck doesn't have AC and didn't come with the lower ratios in the rear, it probabally only has a standard duty chutch which wasn't meant for heavy towing. It may be worth upgrading to the sever duty clutch.

 

[SandburRanch]

My old one ton(1989 chevy, gas 5.7L) is overheating(near the red on long hills) under load on a pretty regular basis. I do not recall it having this trouble before this year. Do water pumps go bad before leaking? Anything else it could be besides the thermostat?

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Water pump impellers can wear to nearly nothing, but to check for pumping capability remove the heater hose supply and elevate it as high as possible. If water pumps out the pump isn't the problem. Replace the radiator or have it cleaned. Being a 89 don't be too surprised if the radiator shop says you need a new one because yours won't tolerate a cleaning.

 

[LD1]

I don't think a fan clutch would be much help. The fan itself is generally out of the cooling picture above about 35mph. The clutch type probably has more to do with fan size and number of blades. The fan could be 5, 6 or 7 bladed with different diameters. A 7 bladed 20" fan would put more of a load on the clutch than an 18" 5 bladed unit. The clutches also tend to disengage at around 2000 rpm of fan speed. While I'm on the subject of low speed cooling comments, the fan shroud is important too for low speed cooling.

I respectfully disagree.

While under normal circumstances this is general true, but under a heavy load, the fan is still able to deliver more airflow even at highway speeds, and still has a lot to do with helping the engine stay cool.

And regardless of what fan is on it, a heavier duty clutch can still be used. It will make the fan run more whereas a lighter duty clutch will let the fan start "slipping" at an earlier rate.

Or even better yet, if you can get a fan from an earlier motor that does NOT have the clutch, that would help out even more. The fan clutch came about to try to help improve economy by taking load off the motor when not needed. But I'd rather have a fan running all the time anyway. And in a 89 1-ton with a 5.7L, I doubt there would even be a noticable economy drop.

 

[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.