Replaced the water pump on my 1999 Dodge Durango today. Also replaced the water inlet tube. It keeps leaking where the tube is inserted into the pump regardless of what I do. The O ring, that came with the tube, seems to be a little on the skinny side, but anything thicker won’t fit into the pump. Would have been easier the have a threaded insert. I don’t think I am supposed to use anything else, but the O ring on the inlet tube, is that correct?
You coat the O-ring with antifreeze before installing.
Tester
I used vaseline
That works too.
Tester
I replaced the water pump on a 360 magnum years ago. I remember the tube with the O-ring. But I don’t remember installing it lol. I don’t recall doing it, but could you not use rtv around the outside where the tube goes into the pump?
I am tempted to do that, but wonder if that is a long-term fix. On the other hand, this thing has 288K miles on it and there is nothing long-term left on it.
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Yeah, the rtv looks kind of sketchy. I have seen it done, but don’t recall if I did that or not. The tube may have already been installed on the replacement water pump - it was from Napa. Been a while ago, so it’s fuzzy.
I think I’d give the rtv a shot if you already installed the o-ring properly (lubed it before install). If it leaks already, you don’t have much to lose lol. Only other option, get another o-ring in case that one got torn or something and reinstall the tube. Slap some rtv on it for good measure!
The problem is, that connection is under pressure from the cooling system.
Tester
Does the old o-ring measure the exact same size as the new one? Both the inner and outer diameter of the “o”, and the thickness of the ring material? The pumps and inlet tubes are probably used in several makes and models and model years, so the o-ring may not actually fit your vehicle. Or somebody might have swapped it with another one at some point. When I purchased a replacement water pump for my Corolla, which requires 2 O-rings, one where it meets the engine, and one where it meets the inlet tube one o-ring was missing entirely, and the o-ring that came with the pump wasn’t the correct size. I had to order two more o-rings.
I’d guess silicone grease (plumbers grease) would work pretty good to coat the o-ring prior to install.
Agree, but I don’t think you’ll have much pressure past the o-ring. Just coolant seeping past o-ring. I could be wrong, it might not work, and I don’t like the way it looks because it just looks backyard and unprofessional. But I’ve seen it done quite a bit and I assume it stopped the seep.
One other option, take the water pump off, return it, and buy one with that tube pre installed. The more I think about it, the more I believe that Napa pump I used already had it installed.
I guess the issue could be a poor quality casting on replacement pump. O ring and install could be fine. Hole where O ring and tube fit is slightly oversized due to casting. 
If it came from Tha Zone - I might take it back and get something better.
Rockauto has a bad return policy, unless a part is defective on delivery. I looked again at the inlet tube and believe there is sufficient space at the indent to place two O-rings on it. It’s a quick and easy try before I go the RTV route. The tube is enamel coated. Not a good surface for any adhesive unless I take the coating off. Looks is not a concern on this car. It’s under the hood.
I like the double o-ring idea if there’s room 
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Problem solved. The tube has an attached (welded) bracket that mounts to the engine block via a bolt. The position and size of the bracket hole prevented the tube from being fully and deeply seated. By re-shaping and enlarging the hole I was able to push the inlet tube a 1/4in deeper into the water pump fitting.
Thanks for posting the sol’n OP. Good diagnostic work there. Proof that sometimes you just gotta bite the bullet and start taking things apart tor find the cause of a problem like this.