Anyone ever had their water pump bolts break? This is the fourth time it's happened. Once causing the fan to hit my rad.

Here's the pesky bolt.


And here is where it's located.

Seems to alsways be the bottom bolt. Though, one time it broke the bottom and it cracked the water pump at the other bolt.

This a common thing? Am I doing something wrong?
It seems to only happen when it's cold. Was -37 C here the other day and had a bit of a hard time starting.

Any help would be apprieciated.

Thanks.

 

I've gotta ask, how come you've had your H2O pump off 4 times? Or does the bolt just break so you have to take the pump off to put in new hardware? Is there room to use studs? That'd be a cool solution.
g

 

If you are not over tightening it sounds like you might need to check on the grade of fastner you are using. Torque should be 18 lbs-ft or 24 Nm. It may be the wrong bolt for that application. Some high grades do not react well to extreme temperature changes. I can not see the top of the bolt to determine the grade but it looks like it might be a high grade, high temperature fastner. There are generally three SAE grades Grade 2 is pretty soft, Grade 5 is common and grade 8 is high strength. The hash marks on top of the bolt signify the grade. None on top for 2, three is grade 5 and six marks is grade 8. Unfortunitly I cannot find which bolt goes in the water pump. If it is in the Service Manual I haven't found it yet.
I just checked your profile and it appears I may be preaching to the choir on this one. Have you run a tap in the hole to see if you are bottoming out before the fastner torques up?

 

Yes I have run a tap and checked the bolt going in to see if it bottoms out. It doesn't. They are metric bolts, so the grade is a little different.
What I figure is they are about equal to grade 5. Guess I'll look for some 12.9. Strongest metric I could find on the net.
I used the same ones that were in it originally. Maybe someone changed it?

And yes, I had to replace the hardware four times.

 

i have my water pump out twice and everything has been fine with my stock bolts

 

I wouldn't suggest this if you hadn't had four bolts to break; but, if it were mine, I would consider drilling and tapping to the next size larger SAE and use grade 5 bolts.

I would suspect either warpage of the block casting where the pump attaches or the surface is not milled true.

 

Hard to tell from the picture for sure, but it looks as though the bolt was half broken for a while and then finally broke completely. Did you check out the stain on the broken piece to see if it broke in stages, etc.?

Since the water pump does not rely on clamping force to seal, I would suggest using thread-lock (or better yet, buy a ny-lock screw) and cut the torque in half. -37 C is cold enough that if you had a faulty alloy in the fastener, it might cause it to fracture under much less stress, but four times would pretty much rule that out.

It doesn't make any sense to me at all. Under what conditions did it break the first time?

 

It always breaks when it's this cold. Usually the first cold spell. We are talking -25c to -40c. Real cold. Truck is hard to start when it's that cold. Maybe the shaking?
I replace the bolt, then it lasts till next year. I am starting to think I may have a bad batch of fasteners. I bought a few at the same time. Have to look at other problems now that I am the only one with it.
I don't know if threadlocker would work with the heat build up? Maybe the red stuff?
Nylock screw? I thought they only made nuts?
Now that I look at it, it does look like it broke in stages. There is some rust on it. I am going to go get some fasteners from a different source. Glad it's not all back together yet.
Might have to wait. -37 tonight. Brrrrr.

Thanks for the help.

 

My '91 did exactly the same thing, except in the summer time. The first time was totally by the surprise, the second time was a couple weeks after replacing the tensioner. Figured the extra spring pressure might have contributed to the problem. The first time, I ended up drilling the lower bolt out and installed a heli-coil. Didn't have M8 so I put in 5/16-18 grade 5. It's within .002", so I figured it would be ok. When it happened the second time, I upgraded to grade 8 and added lock washers on both bolts. Mine didn't have any, don't know how it comes from the factory as it was 7 years old when I bought it. My theory was that maybe one of the bolts had worked loose and vibrated itself in two. Sold the truck a few months ago, so I won't know if the problem ever reoccurs. I wouldn't recommend nylock or loctite since it would make it that much harder to remove if it happens again. My knowledge of cryogenics is very limited, but it's hard to believe that temperature would have much of an effect on the strength of the hardware. It's somewhat comforting to know that I'm not the only one. When it happened the second time, I posted on this board, but no one else had a similar problem.