C1 '58 493 water pump heater hose nipple

[Ted S.]

Was the 3736493 ever produced with a 3/8 npt heater hose outlet? In Paragon's catalog they sell the curved nipple with a 3/8" npt for a 5/8" hose for '58 and a 1/2" npt for '59 and up for a 3/4" hose. I contacted a gentleman that has several old 493 pumps and he doesn't have any that have a 3/8" npt for the smaller nipple. He also looked in his books and can't find any reference to one being produced with a 3/8" npt water pump opening. The TM&JG indicates that '58 had both heater hoses 5/8". Did they use a reducer out of the factory to covert from 1/2" to 3/8"? Was a different water pump used in '58?

Thanks, Ted

[Joe L.]

Re: C1 '58 493 water pump heater hose nipple

Ted-----

What part number does the 1958 AIM show as being used for the waterpump heater nipple?

[Ted S.]

Re: C1 '58 493 water pump heater hose nipple

Joe, the '58 AIM shows 3144968 for the nipple. That's the same nipple shown in my '60 AIM.

There are a couple of revisions in the '58 AIM but I can't find the part there refering to. I think the reference is to the number in the circles on the drawing. For example that would indicate the nut that goes on the fresh air intake for the heater changed from 3140546 to 274754 on 3/17/58.

If my understanding of how to read the drawing revisions is correct, it doesn't show the part changing fro 7/31/57 through 9/22/58. The first date is when the drawing was released and the second date is the last revised date. The same part number shows up in my '60 AIM which has a release date of 5/28/59.

Thanks again, Ted

[Joe L.]

Re: C1 '58 493 water pump heater hose nipple

Ted-----

Unfortunately, that's a nipple for which I have no specs. As a matter of fact, I can't even find that it was ever available in SERVICE. However, it's possible that it was available in SERVICE under a Chevrolet part number. The 3144968 is a Harrison part number; there may have been a Chevrolet part number for exactly the same piece.

[Ted S.]

Re: C1 '58 493 water pump heater hose nipple

Joe, The hose that ran from the water pump to the heater core was 3747132 and the clamp at the water pump is 272852. Any reference to these? If all the part numbers are the same in both the '58 and '60 AIMs wouldn't it indicate that the TM&JG is incorrect in indcating that the '58 had a 5/8" hose and the '59 - '60 had a 3/4" hose?

[Joe L.]

Re: C1 '58 493 water pump heater hose nipple

Ted-----

I can't find anything on the GM #3747132. This was a PRODUCTION-only part number and I can't find any specs for it. However, the GM #272852 search proved somewhat fruitful. This is a Corbin (spring wire) type clamp and it's designed for use with hose with 1-1/16" OD. GM heater hose of 5/8" ID generally had an OD of about 15/16", so I don't think that this clamp would have worked with that hose, even considering for the slight expansion when the hose is drawn over the nipple. Curiously, GM 3/4" heater hose generally has an OD of right at 1-1/16".

[Ted S.]

Re: C1 '58 493 water pump heater hose nipple

Joe, I certainly appreciate your help in looking this up. This all started by looking for a 493 pump with a 3/8 npt. If I would have looked on the next page of the TM&JG they state "The 1958 nipple is 3/8" pipe thread and requires a 1/2" pipe thread sleeve; 1959-60 nipple is 1/2" pipe thread. So it appears the 493 pumps were drilled and tapped for the 1/2" NPT.

It seems the TM&JG is inaccurate though. When looking at the '58 and '60 AIMs the parts numbers in question are the same for 58 - 60 (i.e. Noland's book also states they're the same but I assume part of his basis was the AIM drawings), so it would appear that all three years used the 3/4" hose off of the water pump and the 5/8" hose off of the intake verses the TM&JG position that '58s differed by using a 5/8" hose off of the water pump like earlier models.

The only way the TM&JG could be correct is if the parts themselves were revised without a part number change. Also the AIMs only indicate 1 part for the nipple off of the water pump verses a sleeve and a nipple on the '58 so the part number would have to of included both pieces. Having been in engineering this doesn't sound probable.

Would you agree with my position based on the evidence?

Thanks, Ted

[Joe L.]

Re: C1 '58 493 water pump heater hose nipple

Ted------

Yes, I would agree with your position. However, my knowledge of C1's is very limited. Vaguely, way back in my memory someplace, it seems to me that, perhaps, there were different heater hose sizes used for the 1958 model year. It may be that early cars used 5/8" on both heater hoses whereas later used 5/8" on the top and 3/4" for the lower. I don't think that the waterpumps were any different, though; just the fittings/adapter used. It may be that some of this information is not in the copy of the AIM that is available.

[William M.]

Re: C1 '58 493 water pump heater hose nipple

Joe and Ted,

I've had many 3736493 water pumps(like several thousand) over the last 30 years. 99+% of them had the 1/2" NPT(National Pipe Thread) heater hose fitting hole. I've had several that have had the 3/8" NPT heater hose fitting hole. And, I've had some with the 1/2" NPT that have a reducer sleeve(bushing) to 3/8" NPT. The 3/8" NPT heater hose fitting was used on all 1957 Corvettes and into 1958 Corvette engine production until the change from 5/8" ID heater hose to 3/4" ID heater hose.

1957-1960 Corvettes only used the "493" water pump with no casting date,no "T",no reinforcing webs and no bypass hole on top. The other variations of the "493" water pumps were used on other Chevrolet applications(passenger cars and trucks). Some had a "T"(also "TX") embossed or cast below the 3636493 casting number and were made in Tonawanda,NY for Tonawanda small block engines. Some had a casting date(usually a 1959 date). Some had two reinforcing webs on the driver's leg of the water pump and were for truck application. And, some had the boss tapped on the top for a 3/8" NPT water pump bypass fitting and were for truck application(this was replaced by the rarely seen 3757248 water pump with a 1/2" NPT water pump bypass hole on the top).
Hope this helps.
Bill Mock #93