3757248 Water Pump

[William M.]

Lately there has been much discussion about 3782609, 3839175 and 3859326 water pumps on the NCRS Technical Discussion Board. Please look at the four pictures of a 3757248 water pump. One picture shows the difference in the bypass fitting boss between a "248" water pump on the left and a "609" water pump on the right.
Your comments please.
Regards,
Bill Mock #93

[Twan B.]

Re: 3757248 Water Pump

What year Corvette!!

Twan

[Joe L.]

Re: 3757248 Water Pump

Lately there has been much discussion about 3782609, 3839175 and 3859326 water pumps on the NCRS Technical Discussion Board. Please look at the four pictures of a 3757248 water pump. One picture shows the difference in the bypass fitting boss between a "248" water pump on the left and a "609" water pump on the right.
Your comments please.
Regards,
Bill Mock #93

Bill------


I've never seen this casting before. I'll bet it was a "truck-only" piece. If so, it represents some further support for my theory that Chevrolet considered the external by-pass pumps used on cars, including and especially Corvette, to require a pulley relief. However, apparently, they didn't see that need for truck applications.

The '609' and '326' pumps, which were the primary external by-pass pumps used on Corvettes and those few other passenger cars that used such pumps both have the cast-in pulley relief. The 3757248 and the 3839175, which I theorize were probably primarily truck pumps (except for those used on L63-64 Corvettes) and don't have the cast-in relief (except for apparently later SERVICE '175' castings).

Since you're the man that's probably seen more waterpump castings than just about anyone else out there, I have a few questions for you to help me in sorting this all out:

1) Of the original '175' castings with 1/2" NPT bypass that you've come across, are all without the pulley relief?

2) If any of the original '175' castings have the pulley relief, does it appear cast-in or created later by machining?

[Jack H.]

Re: 3757248 Water Pump

I won't put words in Bill's mouth but I'll offer what I know from my experience, Joe.

First, I said in a prior thread that I'd never seen a '175 pump with 1/2" NPT bypass hole. Bill enlightened me that he has and the number of such was QUITE small...

Second, I've never seen a '175 pump without the pulley clearance depression on the front of the boss. Bill enlightened me that such critters apparently DO exist!

Third every '175 casting I've seen/had provided a front boss depression for additional pulley clearance. ALL were molded in and NOT machined in.

Taken together, these facts open a new page in the water pump book. That's a page that says there were running change(s) to the '175 castings' mold. Interesting...

[Jack H.]

Re: 3757248 Water Pump

Yes, I've seen 3-4 of these pumps and simply walked away because they're not documented (or even 'hinted' at) as being Corvette or Chevy applicable...

[Joe L.]

Re: 3757248 Water Pump

I won't put words in Bill's mouth but I'll offer what I know from my experience, Joe.

First, I said in a prior thread that I'd never seen a '175 pump with 1/2" NPT bypass hole. Bill enlightened me that he has and the number of such was QUITE small...

Second, I've never seen a '175 pump without the pulley clearance depression on the front of the boss. Bill enlightened me that such critters apparently DO exist!

Third every '175 casting I've seen/had provided a front boss depression for additional pulley clearance. ALL were molded in and NOT machined in.

Taken together, these facts open a new page in the water pump book. That's a page that says there were running change(s) to the '175 castings' mold. Interesting...

Jack------

I have no doubt that the later SERVICE versions of the '175' pump (i.e. those with dates and 3/4" NPT bypass fitting) have the pulley relief as a feature of the casting. However, what is of more interest is if all the original versions (i.e. no dates and 1/2" bypass) have the relief and whether that relief is a feature of the casting or machined.

[William M.]

Re: 3757248 Water Pump

Joe and Jack,
The only undated "175" water pumps with 1/2" NPT bypass fitting boss that I have had(only two since 1978) and have personally seen have had the bypass fitting boss rounded on the front without the pulley relief. Two pictures are of a late "175" water pump with the cast pulley relief on the 3/4" NPT bypass fitting boss and dated(in this case: k13(November 1,1973)).
Also, two more pictires of the 3757248 water pump bypass fitting boss. One of the boss itself and the other comparing the bypass fitting boss on a "248"(on the left) and a "609" on the right.
Regards,
Bill Mock #93

[Joe L.]

Re: 3757248 Water Pump

Joe and Jack,
The only undated "175" water pumps with 1/2" NPT bypass fitting boss that I have had(only two since 1978) and have personally seen have had the bypass fitting boss rounded on the front without the pulley relief. Two pictures are of a late "175" water pump with the cast pulley relief on the 3/4" NPT bypass fitting boss and dated(in this case: k13(November 1,1973)).
Also, two more pictires of the 3757248 water pump bypass fitting boss. One of the boss itself and the other comparing the bypass fitting boss on a "248"(on the left) and a "609" on the right.
Regards,
Bill Mock #93

Bill------


It looks like the 3757248 does, effectively, have a pulley relief that's a feature of the casting. It's a different sort of configuration than the '609', '326', or the version of the '175' with the relief, but it looks like it would accomplish about the same thing.

I understand the reason for the change from the '609' casting to the '175' and '326'-------a larger boss was necessary for 3/4" NPT tappings. How the 3757248 figures into it, I can't figure out, though. However, I still don't understand the need for the other pump castings. There may have been minor INTERNAL changes, though.

[Michael H.]

Re: 3757248 Water Pump

Please look at the four pictures of a 3757248 water pump. ,
Bill Mock #93

Just a guess but I would say the 3757248 was first used on HD trucks in about 1958? It was possibly/likely the correct pump for 61 Corvette also.