3859326 Water Pump Install on a 65 L76

[Jack W.]

OK, so I got ahold of the correct (3859326, 1/2" NPT, undated) water pump for my 65 (April build) L76. I recall reading somewhere (here, no doubt) that these pumps came from GM with a plug or dowel of sorts to block off the internal bypass when used in a SHP config? Or did I imagine that? If this was the case, what if I don't block the internal bypass when I install it? (It sure did not come to me with such a thing). Thanks, you guys always seem to know just what I am asking, even if I am asking it wrong!

[Joe L.]

Re: 3859326 Water Pump Install on a 65 L76

Jack-----

GM SERVICE waterpumps of the 3859326 casting were supplied with 2 plugs. One was a 3/4" NPT pipe plug to plug the upper bypass fitting if the pump was used on an engine with internal bypass (later '326' pumps all used the 3/4" NPT upper fitting). Also included with the water pump was a 3/8" dowel pin and this was the plug for the internal bypass if the pump was used with an engine with external bypass.

I don't know if earlier '326' castings had the provisions for internal bypass, or not. I think that they did, but I'm not certain. In any event, it's easy to tell. Simply look at the passenger side leg and look to see if there is a 3/8" hole below the large coolant passage hole. Also, check to see if there is a matching hole in your block. If either one doesn't exist, then your internal bypass is, effectively, "plugged".

If both holes are there, then you can install a 3/8" dowel in the hole described in the water pump leg. I really don't think that this is absolutely necessary since I don't think that having both "bypasses" would really hurt anything. But, you can do it if you wish.

[Jack W.]

Re: 3859326 Water Pump Install on a 65 L76

Thanks Joe. My block, an "HH" block, has the internal bypass hole, and the undated "326" water pump has a matching hole, just to add to your factoid database. If you say not a big deal, I trust that advice and I guess I will let it go. I have bigger fish to fry right now anyway - the freakin' bolts that hold the old pump's flange to the pulley and fan are not budging one micron, and I foolishly have the whole thing off the car (I now suspect having the belts still snug against the pulley would have been a tremendous help . . . . .)

[Tracy C.]

Re: 3859326 Water Pump Install on a 65 L76

Jack,

Shoost a little WD-40 on the bolt/nuts and go after it again tommorrow. Hold the pump from turning by using another wrench on the bolt adjacent to the one you are trying to loosen.

tc