Vortec 7.4 keeps blowing up water pumps

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Reluctanse

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Today was #4 and the most spectacular, explanation below, but first, pictures

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Why would my truck keep blowing up water pumps? Never seen anything like this before.

First pump cracked by where it attaches to the block last november, while I was doing a crank relearn. At ~4500 rpm a burst of steam came from under the hood and I found this:
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Being the pump that was on the truck when I bought with ~175k miles on it, I didn't think too much about it.

Pump number 2 was a Duralast from Autozone. It didn't crack, but started weeping coolant after just running in my driveway, at about the same spot.

Pump number 3 was a warrantied replacement Duralast, that failed at the same spot the first one did, and doing the same thing.

Pump 4 was a Napa unit after I returned Duralast #2 in disgust and drove across the street. Exploded at about 4k rpms, again, no load, in my driveway.

Other weird cooling issues since I bough the truck:

-blew the lower rad hose while pulling my trailer up a pass. It ran really close to the AIR pump pulley and wore a hole in it. Thought nothing of it. But the truck was getting hot as well, about 230F, before I pulled off at the gas station.
-blew the hose clamp APART on the lower rad hose after installing pump #3, on a short drive. Figured the hose clamp failed.

So what the heck you guys.

My only theory at this point is a blown head gasket sending too much PSI into the coolant system and BOOM.

Help!!
 

BNielsen

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I would think a blown head gasket would blow out either the radiator or possibly the overflow tank before it would shatter a water pump like that?

Could it possibly be a belt tension related issue? Like maybe the belt is tight and when it goes under heavy load it cracks? Hell of a thing regardless of the issue,
 

Piratehunter

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Im inclined to think a bad pulley or tensioner transferring too much pressure on the impeller shaft. Does the PS pump pulley line up with WP pulley, and the crack pulley on a flat plane? Got a straight edge that will catch the outer edges of those and not rock or have a gap in the inner edges.
 

454cid

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Possibly the clutch/fan out of balance somehow? When I put a Gates pump on my truck it lasted a year or two before the seal went, but it didn't break the casting.

When replacing the pump, are you getting all the old gasket material off the block? If not, I wonder if it could be sealing, but still putting a tension in the pump casting causing a crack.

Did your radiator get trashed?
 

HotWheelsBurban

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Maybe there is metal fatigue or a casting flaw? Seems hard to believe you'd keep having the same thing with different pumps though. I would look at the pulleys and tensioner too, to verify they're not off axis somehow and making too much tension/stress/force on the pump. And that all accessory shafts are straight and true. Even a few thousandths off axis can make a lot of force at higher rpms.
 

Reluctanse

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Yeah the radiator ate it on this last one.

The spectacular failure of the napa pump does lend towards seeming mechanical issue, pulley/ps pump/tensioner etc, but the 3 other failures make me not so sure. Especially the first duralast pump, which never actually cracked. It would only weep coolant once at temp at higher revs. Coupled with multiple hose failures/blowoffs, it seems like a system pressure issue.

I do think a new fan clutch is in order, it's been on the list anyways.

When the first pump went, it was with all the stock belt/tensioner/idler pulley stuff, and the AIR pump still installed.

When that went, I had wanted to do some accessory clean up anyways, so I got rid of the AIR pump, got a new tensioner and idler, and a belt. the belt is shorter than the stock one, but alignment seems fine? I've certainly idled it quite a bit this way, and again keep in mind the first pump did not explode.

first pump and 2nd duralast looked like this
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first duralast SEEPED only at that spot, but did not crack.

original belt and tensioner and AIR pump setup:
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Updated pulley/tensioner setup without air pump
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I thought a lot about this over dinner... especially with the blowing radiator hoses, it really feels a system pressure related issue, more than something mechanical binding enough to cause this.

I guess one thing I could test, once I replace the pump again, is maybe some revs with no belt drive hooked up? Also no fan/clutch... I will be getting a new fan clutch for sure, as well as a radiator, because well I have no choice on that one.

Radiator cap somehow? It doesn't feel like it's bad...

Edit: but then again I think with how suddenly and violently the last pump failed that out almost has to be a mechanical issue causing it..
 
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HotWheelsBurban

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One common factor I see is, you're using the same fan blade. Is it bent or out of balance? A good upgrade is the 11 blade fan from a later year Tahoe or similar.
OP's truck is a big block, aren't the Tahoe fans like the 4.3/5.0/5.7 small block Vortecs use, the ones that have the fan clutch with the giant nut that threads onto the water pump snout???
If it IS the same fan, would be easier to find one though.
 

454cid

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OP's truck is a big block, aren't the Tahoe fans like the 4.3/5.0/5.7 small block Vortecs use, the ones that have the fan clutch with the giant nut that threads onto the water pump snout???
If it IS the same fan, would be easier to find one though.

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.
 
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