Water Pump Leak, small crack in rear of housing

[Oxyacetylene]

I recently used my truck to pull an equipment trailer and tractor on a couple hour trip. On the way back I stopped and noticed it was dripping coolant. Bought some at the gas station and filled the overflow tank between the sight glasses. Within the next 2 hours it had leaked all of that out. The truck never ran hot though. When I got home and had time to look at it, I discovered that on the rear of the water pump housing, there is a tiny hairline crack. I feel like this may have developed at least 3 years ago and just now got worse with me actually working the truck some. If I think back a few years to when the winter temps dipped into the mid teens, I remember it having a very slow drip. At the time I thought it might have been a loose hose. So now I need to replace or repair the water pump. Questions for those of you who have already:

• Any particular brand that I should stay away from? I see I can get one off eBay for under $120 including shipping. Looks like a no-name replacement.
• Has anyone disassembled the actual water pump, taken the rear of the case off? I need to check it with a magnet to see if it's steel or cast iron. If it's mild steel or aluminum then I think it could be TIG welded. If it's cast iron, maybe brazed?
• Looks like I would need to remove the fan blade in order to replace the water pump belt? I find it a little interesting that the alternator has a double belt and the water pump only a single. Seems you would want the redundancy there too.

 

[simp5782]

Pump isn't common aftermarket. It is quite different from a common 3116 pump. Not too difficult to do. Adeptape has a video on it as well.

Comparison picture of the lmtv 3116 pump vs one if you got one off ebay

I have one with a crack as well. Pretty simple job. I had it off in around 30min

 

[Oxyacetylene]

Pump isn't common aftermarket. It is quite different from a common 3116 pump. Not too difficult to do. Adeptape has a video on it as well.

Comparison picture of the lmtv 3116 pump vs one if you got one off ebay

I have one with a crack as well. Pretty simple job. I had it off in around 30min

Ah OK, good to know the cheap aftermarket variety will not work. I haven't taken mine off yet, but I see it has two numbers on the back housing: one for "with hole" and one for "without hole." I'm wondering if that is the difference. I can't read the numbers without taking it off. Yours is cracked a lot worse that mine, but I am afraid if I try to keep driving mine that it would turn into that. Is the rear of the housing cast iron?

 

[NDT]

Yes the fan has to come off to replace the belt. Not fun, I did a thread on it about 4 years ago. Involves lining up the access holes in the fan clutch with the allen screws and working blind to remove them.

 

[Oxyacetylene]

Yes the fan has to come off to replace the belt. Not fun, I did a thread on it about 4 years ago. Involves lining up the access holes in the fan clutch with the allen screws and working blind to remove them.

Hmm, tempted to just leave my belt as is for now. It's not cracked, but it's at least 5 years old at this point. Link me to your thread if you have it handy? I'll keep digging through search results if not.

 

[simp5782]

Its cast iron. You could weld it up. Knowing my luck I would fix the crack then 2 weeks later the weep hole would start leaking anyway

 

[Oxyacetylene]

Its cast iron. You could weld it up. Knowing my luck I would fix the crack then 2 weeks later the weep hole would start leaking anyway

OK thank you! Yeah maybe I'll look at welding it up. Good preheat and slow cooling and it might do OK. Now just a matter of finding time to fix it.

 

[Ronmar]

What Simp5782 said. they modified the LMTV cooling to send bypass coolant to the trans cooler/heat exchanger, which is why these engine take so damned long to warm up(gotta get the trans warmed up also). it doesn't look too difficult to mod a standard 3116 pump as they simply cutoff the smaller/upper bypass hose nipple and installed a freeze plug. Like in the pics Simp posted, the hose barb needs to be short enough to clear the bypass pipe that runs down to the heatex from the bottom of the thermostat housing... I have contemplated reverting the cooling system back to OEM 3116 and feeding the heatex coolant flow from another source to allow the engine to cleanly come up to full op temp as Cat intended...

 

[Awesomeness]

1. The rear pump housing is aluminum.
2. The reason the alternator has 2 belts isn't redundancy, it's because two belts are needed to handle the force. Water pump doesn't require as much.
3. Yes, you have to take the fan off to get the water pump belt changed, but you don't need to remove the belt to change the pump.
4. I have a used pump with that rear housing brand newly replaced, that I would sell if you want.
5. Take a look in my troubleshooting document here in my signature. It's certainly not always the case, but that pump housing cracking can be a sign of driveline problems, that can escalate until it destroys the engine. That's why I have the extra pump! I had the pump crack, fixed the housing, then cracked the engine block soon after. New engine came with a it's own pump, now I have 2, haha.

 

[Oxyacetylene]

1. The pump housing is aluminum.
2. The reason the alternator has 2 belts isn't redundancy, it's because two belts are needed to handle the force. Water pump doesn't require as much.
3. Yes, you have to take the fan off to get the water pump belt changed, but you don't need to remove the belt to change the pump.
4. I have a used pump with that rear housing brand newly replaced, that I would sell if you want.
5. Take a look in my troubleshooting document here in my signature. It's certainly not always the case, but that pump housing cracking can be a sign of driveline problems, that can escalate until it destroys the engine. That's why I have the extra pump! I had the pump crack, fixed the housing, then cracked the engine block soon after. New engine came with a it's own pump, now I have 2, haha.

I'll check through that thread. I vaguely remember when that happened to you. I didn't mention it above, but the outside bolt that mounts the alternator is missing on mine, so alternator rests inwards a little. That may have contributed to it. Good 'ole expedient fix done by the gov't I guess. I just never noticed it until I was looking closely at the water pump area. I may indeed be interested in the water pump if you want to shoot me a PM with a price. It will probably be a while before I get mine off the truck to further check it out.

In glancing over your document you linked, you talk about balancing the drive shafts. That's something I should probably look at doing either way. For what it's worth, I have found that if I disconnect the CTIS and inflate the fronts to at least 60PSI that the truck is noticeably smoother on the road. When I got my truck from auction, the toe in was way too much and I adjusted that out too. I do sometimes notice a vibration that seems to fade in and out. It could be tires, but could be something like drive shafts too. Thanks for the heads up on that.

 

[ckouba]

Driveshaft balance made a large improvement on my 1088. Didn't clean it all up but made a large improvement. $pendy, but ask around- the consequences are even worse.

I paid ~$1100 for all new universals, one section being rebuilt, and everything balanced.

 

[NDT]

Hmm, tempted to just leave my belt as is for now. It's not cracked, but it's at least 5 years old at this point. Link me to your thread if you have it handy? I'll keep digging through search results if not.

FMTV Water Pump Belt Replacement

I tackled this today as my belt was OE Cat from 1998. That's runnin' on borrowed time. As usual, this was not a simple task. Yes the fan blade has to come off. If you are familiar with working with fasteners you cannot see, you can unbolt the fan by reaching through the blades. Otherwise...

www.steelsoldiers.com

 

[AllenF]

Might sound mickey mouse but you could consider JB weld, it is amazing and since this is a low stress and low heat area may work out well. My $.02.