Vortec 7.4 keeps blowing up water pumps

[Reluctanse]

Ok, but how did the first pump go bad? It didn't crack or explode did it? If it was a leak, I wouldn't think that to be out of the ordinary. What was the different setup for the others? I assumed it was what you had pictured with the air pump gone.

First pump failed exactly the same way as the next 2, cracked through on the ear near the block, at about 4k rpms.

This is the first pump, both Duralast's failed in exactly the same spot. When this happened, I was still on the belt setup that was on the truck when I bought it.

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I think actually the autozone pumps might have better castings.... the first duralast didn't actually crack, which is partly why this took me so long to figure out. It was just starting to separate there when I figured it out and pulled it. The 2nd duralast cracked EXACTLY as the above picture, and pretty fast. The napa pump exploded spectacularly almost immediately.

To the rest, I'm going to start hunting for the correct alternator bracket so i can use the federal style tensioner and routing. I wanted to do this anyways. I don't think it's the root of my issues but I will be doing some thorough step by test testing to make sure.... If I can't find one any time soon I might put the air pump back on, as much as that pains me, but we'll see. I really don't think this is the problem.


For that alt bracket, i see lots even reprods that say they fit the 4.3/5.0/5.7, but none listed for the 7.4. Internet searches/google seems more retarded than ever these days and it's all promoted ads when I search for anything. I'll keep digging, but right now I can't even find the part number for the 7.4.

Maybe one of you wizards knows if the small block vortec bracket is the same-

 

[454cid]

No the small block brackets are different. They're also aluminum not cast iron.

You're best bet for finding the part number is from one of the dealers that sells parts online and lists part numbers.

 

[Spareparts]

I have one in my garage. Here is the only number on it.

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[454cid]

I have one in my garage. Here is the only number on it.

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How appropriate considering your username, lol.

 

[Schurkey]

1. Hopefully get my shattered water pump replaced under warranty by Napa. Shhhhhhhhhh....

That's not a warranty item.

2. Throw some kind of goup on the radiator to keep it from completely leaking while I test all these scenarios (will replace rad when everything works)
3. Reinstall water pump, connect hoses. Leave Fan, clutch, belt OFF. fill system with water and leave rad cap off
4. Idle run up to temp, without fan or water pump or any accesories
5. Rev it up a few times before it gets super hot

Marvelous way to create localized hot-spots and crack castings.

7. Install accessory drive, but leave fan/clutch off, test again to 4k rpm's.

Now you're talking. Water pump is pumping, coolant is circulating, but without load from fan/clutch.

8. If all is good, install NEW fan and clutch, test again
9. See where we are at, and what has failed.

Every broken water pump I've been around has been a result of an unbalanced fan, or disturbed airflow across the fan so that the fan loading isn't symmetrical. (Except for the ones that broke due to crash damage, of course.) I'm thinking of a sheet of cardboard across half the radiator in the winter. For example, the left side of the fan has blocked airflow while the right side doesn't. As each blade spins from the "dead zone" to where it bites into air, the blade gets stressed and that passes through to the pump shaft and bearings, and into the casting. Hard on the fan, too.

Usually, the fan has lost a blade. Yours hasn't, which makes it unusual. Therefore, "I guess" the root cause may be unusual--failed accessory, improper tensioner, etc. But my best gues is, it's the fan.

 

[HotWheelsBurban]

That's not a warranty item.


Marvelous way to create localized hot-spots and crack castings.


Now you're talking. Water pump is pumping, coolant is circulating, but without load from fan/clutch.


Every broken water pump I've been around has been a result of an unbalanced fan, or disturbed airflow across the fan so that the fan loading isn't symmetrical. (Except for the ones that broke due to crash damage, of course.) I'm thinking of a sheet of cardboard across half the radiator in the winter. For example, the left side of the fan has blocked airflow while the right side doesn't. As each blade spins from the "dead zone" to where it bites into air, the blade gets stressed and that passes through to the pump shaft and bearings, and into the casting. Hard on the fan, too.

Usually, the fan has lost a blade. Yours hasn't, which makes it unusual. Therefore, "I guess" the root cause may be unusual--failed accessory, improper tensioner, etc. But my best gues is, it's the fan.

Fan might be slightly bent on one or two blades....

 

[HOPPER]

Be sure the anti-freeze is the correct 50/50 ratio, it may be too pure.. If so, it will wash the bearing in the pump by leaching the seal.. I would check the harmonic balancer also, if the rubber insulators on it are off balance ANY, it will transfer to the pump via the belt.. A pressure test on the coolant system would be a good idea, to be sure no cylinder pressure is entering the coolant system..

 

[Reluctanse]

Realized I never replied here:

It was 100% the fan clutch causing the issue. New fan clutch, problem solved.

 

[Supercharged111]

Way to leave us hanging! Did Napa give you a free pump or not?

 

[Reluctanse]

Way to leave us hanging! Did Napa give you a free pump or not?

You know, I ended up just ordering a new one, I didn’t have it in me to ask on that one. Blame @Schurkey