Jimbad

Hi, All,
I'm about to jump out of my skin. I have just spent (misspent?) two hours on the web and in the Adams book looking for water pump info for my '66, so, once again, I am turning for help from the Forum.

My car is a 327/300 with AC. The original water pump was replaced with an aftermarket unit about 20 years ago so I can't judge by what's there now. The fan, however, is original and it takes 4 bolts.

Here are my questions:
1- Should the hub on the water pump have 4 or 8 bolt-holes?
2- John Z points out that the numbers on the pump cannot be seen when the pump is in place but I would just like to know what number(s) should be on the correct pump.
3. Does an AC-fitted car have a special pump?
4. The threaded hole in my current pump, which takes that little (bypass?) pipe, is 3/4" in diameter. Is that correct?

Thanks,
Jim

Powershift

Jim:

I can help answer some of your questions.

For a 1966 327/300 car, the original water pump should be a #3782608. The hub should have 4 holes. Replacement hubs have 8 holes and will also work, but are not original.

AC cars do not have/require special water pumps.

A #608 pump does not have a threaded hole for a bypass. This bypass was used for the SHP (special high performance) engines, like the 327/350 HP.

If you require a bypass for some reason/change, then you may want the 327/350 HP engine water pump, which is a #3859326. The hole is threaded for 1/2 NPT fitting (which is approx 3/4 inch diameter hole)

To get a correct water pump call Bill Mock at (918) 333-0748, or ChevyCool at (480) 720-8000, or Arthur Gould Rebuilders at (631) 269-0093.

Hope this helps.

JohnZ

1. 4 holes is "correct"; most rebuilts and many GM Service replacements had both bolt patterns. Minor deduction for both patterns.

2. The correct pump is casting #3782608 (without any reinforcing ribs/fins on the front - only Tonawanda 3782608 pumps had them, and they weren't used on Corvettes).

3. Nope - A/C cars used the same pump as non-A/C.

4. Your 300hp pump shouldn't have any bypass fitting - that feature was only on 326 pumps, which were used on the 350/365/375hp engines with a bypass hose nipple in the front of the intake manifold. Photo below is a '67 300hp, but your '66 300hp should look exactly the same (except for the shape of the valve covers) - no boss on top of the pump for a bypass fitting, and no bypass nipple on the intake.

65 vette dude

I believe the correct pump for your motor is 3782608. Very common pump, and I 'm pretty sure it was used on both non A/C, and A/C cars. It does not have a bypass. The bypass was used on the higher HP S/B's. Are you sure the W/P on your car now is a aftermarket? The reason I ask is, the corvette specific 3859326 pump has the small bypass hole that measures 3/4" across and takes a 1/2' I.D. bypass hose and was used on 63-67 340-375HP small blocks. That pump is rare and desirable. There is another, more common 326 pump, with a bypass that measure's 1" across, and was used on truck motors, and they are fairly common.

Jimbad

Firstly, I thank you guys for taking the time to write and putting me back in my skin!. This Forum (people) is just one terrific resource.
Secondly, I just checked photos of my engine taken before I began my restoration and I have one big hose and one smaller hose going to/from the pump. I was describing the small-hose fitting as the bypass; maybe that was wrong. John Z will tell me. (I don't yet know how to post pics here so I cannot show you what I am talking about.) There is a large screwed-in plug on the pump and maybe that is where the bypass is for certain applications.
Thanks Again,
Jim

65 vette dude

Jim it sounds like you have one large hose that goes to the bottom of the rad, and one small hose on the side that goes to the heater, and no bypass. Like you said, it's probably a aftermarket with a brass plug in where the bypass is located. I may be wrong about this but I think I remember that GM didn't start date coding water pumps until November in 1965. If your interested in a 608 pump that might be date coded correct for your car, you might give Arthur Gould a call. He's been rebuilding pumps for classic cars for a long time, and uses only top notch parts. I got my 326 pump from him. Google Arthur Gould Rebuilders.