Vortec 7.4 keeps blowing up water pumps

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Reluctanse

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First, thank you all for the responses! They have definitely helped me think through this process. You all are great!

I have formulated a plan to start testing through the possibilities, let me know what you all think.

1. Hopefully get my shattered water pump replaced under warranty by Napa. Shhhhhhhhhh.....
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
6. Put radiator cap back on, rev to 4k a couple more times
7. Install accessory drive, but leave fan/clutch off, test again to 4k rpm's.
8. If all is good, install NEW fan and clutch, test again
9. See where we are at, and what has failed.

Let me know what you think-
 

454cid

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Updated pulley/tensioner setup without air pump
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Ok, here's a theory. You're still using the tensioner for the CA Emissions smog pump. It has a smooth pulley, and it's on the loose side of the belt, as the crank turns clockwise. The Federal Emissions engines, like mine (most are 49 state) use a ribbed pulley and push the belt out. The belt can't/won't run off the ribbed pulley. I bet yours is drifting off the pulley if not breaking, and the engine is yanking on the pumps so hard it breaks or cracks them.

Your passenger side bracket is different, but I wonder if it would still allow the Federal Emissions tensioner to bolt up. If not, the correct bracket is easier to find than your CA bracket.
 
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HotWheelsBurban

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There are at least two 11 blade fans. There's a white one, and a black one. I have the black one, and its listed as a 454 fan. I think it was either a late van fan (for the 454) or it was retroactively applied to the 454.

The bolt patterns on the gas engines are all the same and will fit either style clutch.
Good to know! Learn something new every day....
 

Vanishing Point

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I'll take a stab at it, just in case all else fails. But by any chance did someone accidentally put the fan blade back on backwards when it was put back together? Sure looks pretty close to the radiator in one of your pics and I couldn't tell if there was a fan shroud on it! But what I'd know, I have a 5.7L 350ci and not a 7.4L 454ci. Just my 2 cents worth.
Anyway good luck with your fix, and do let us know how it all turns out.
 

termite

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I'd test the cap and check for combustion gas in the coolant after verifying pulley alignment etc. upon reassembly. Perhaps even blow some air through the coolant passages while apart just to ensure they are clear and not obstructed resulting in pressure spikes.

Hope napa will warranty that exploded pump for you at the least.
 

Erik the Awful

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I'd replace the tensioner just in case. If it's rolling smoothly most of the time and occasionally locking up for a split second, that's going to hammer the water pump and other accessories.

Second, I'd check the balance of the water pump. Spin it by hand on a water pump without the belt and see if it's out of balance.

It is not a pressure problem. If it were you'd blow out an end tank before it would crack the water pump.
 

Reluctanse

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Ok thanks again everyone I feel like I’m getting somewhere.

It’s obvious I need a new fan and clutch, so I’ll get that going-

There are at least two 11 blade fans. There's a white one, and a black one. I have the black one, and its listed as a 454 fan. I think it was either a late van fan (for the 454) or it was retroactively applied to the 454.

The bolt pattern on the gas engine fans are all the same and will fit either style clutch.

Do you have a part number? Or is there a specific year I can look at for the Tahoe fan? And yeah I have a 454 so-

Ok, here's a theory. You're still using the tensioner for the CA Emissions smog pump. It has a smooth pulley, and it's on the loose side of the belt, as the crank turns clockwise. The Federal Emissions engines, like mine (most are 49 state) use a ribbed pulley and push the belt out. The belt can't/won't run off the ribbed pulley. I bet yours is drifting off the pulley if not breaking, and the engine is yanking on the pumps so hard it breaks or cracks them.

Your passenger side bracket is different, but I wonder if it would still allow the Federal Emissions tensioner to bolt up. If not, the correct bracket is easier to find than your CA bracket.
So the first pump went out on the original setup, with air pump, old tensioner and belt… later pumps went out on a different setup. I have the air pump stuff still and could put it back on, just to have correct routing. I looked at brackets for the federal setup and eBay wants like $300 which just seems criminal. I would like to get the correct setup at some point but not at that price, just need to keep eye on the yards around here. Maybe I’ll put the air pump back on for now. I don’t think it’s the new tensioner itself.

Getting fairly certain now that it’s the clutch.
 

454cid

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Do you have a part number? Or is there a specific year I can look at for the Tahoe fan? And yeah I have a 454 so-

This is a post in my thread about what I did. If you scroll up, you can see explanation and pictures.


So the first pump went out on the original setup, with air pump, old tensioner and belt… later pumps went out on a different setup.

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.

I have the air pump stuff still and could put it back on, just to have correct routing. I looked at brackets for the federal setup and eBay wants like $300 which just seems criminal. I would like to get the correct setup at some point but not at that price, just need to keep eye on the yards around here. Maybe I’ll put the air pump back on for now. I don’t think it’s the new tensioner itself.

Getting fairly certain now that it’s the clutch.

Yes the used Vortec 454 parts got super stupid expensive a few years ago. You're probably finding the same auctions I did, where it's the whole serpentine setup. I did find a completed auction for the passenger side only, that was cheaper. The key is probably to find the part number and search using that... or finding it in a local yard.

As far as your new tensioner, it's not that its new or old, it's that the design may not be adequate for the job without the air pump. High revs are going to take tension off the belt and that design of tensioner has no way to control the belt other than tension.
 
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