70 L-46 radiator

**Joe L.** · July 4, 2005, 02:00 PM

Re: 70 L-46 radiator

Dennis-----

Most, if not all, 1970 Corvettes with L-46 used a copper brass radiator of GM #3018803. This radiator has a 26" core width and an integral filler neck on the right side tank. It has NO provisions for transmission oil cooler. This has been a very difficult radiator to find. It was used in PRODUCTION during 1969-72 only and it was discontinued from SERVICE in June, 1974, and repalced by the GM #3108802, a nearly identical radiator except that it has oil cooler provisions.

I know that DeWitts offers a reproduction of the above radiator in aluminum. I don't know if they currently offer an exact reproduction in copper/brass, though. If they don't, I expect that no one else does.

The radiator support for the 3018803 and 3018802 radiators is not the same as the support for cars with the 3155316 aluminum radiator. The basic frame is the same, but that's where the similarity ends. The 3018803 uses a completely different mount system than the 3155316 and so the supports are different in this regard. Also, the 3155316 support uses welded-on plates which, effectively, reduce the width of the opening. These could be removed from a 3155316 support, of course. However, you'd then have to remove the lower radiator supports and weld on the "stirrup" style supports used for the 3108803. Then, you'd have to drill new holes in the upper portion of the supprt for the mounting bolts for the upper "stirrup" mounts. So, a conversion could be done, but it would be quite a bit of work, you'd have to find a source for the "stirrup" mounts, and you'd need to get all the correct dimensions for modifying the support.

1968 radiator supports are different than 69+. They are one-year-only items. They are what you might call "crossover" or "transition" parts---they contain design elements "akin" to both the 66-67 big block supports and the 69+ supports. They are not directly interchangeable, though, for any other model year and no other mode year support is directly interchangeable to a 1968.

**Jack H.** · July 4, 2005, 08:36 PM

Regarding the fan/clutch...

you mentioned your fan and fan clutch you have for your '68 came from a '71 SB A/C car. Bad news here pardner...

That was the first use of wide bolt pattern hubs on SB fan clutches. If you have a factory correct water pump on your '68, it's NOT going to match the narrow bolt pattern hub on the stock water pump. That's UNLESS the original pump has been rebuilt with a service replacement dual bolt pattern hub pressed onto the water pump's input shaft.

**Dennis D.** · July 4, 2005, 08:52 PM

Re: Regarding the fan/clutch...

Joe. Thanks. I'll search for a correct rad, and if I can't find one, I'll probobly use the dewitt alum version.

Jack. Sorry for the confusion. My car's a 70 with a few "creative changes". The radiator, and I believe support, are 68. The Water pump, clutch, fan, pulleys are 71. Have all the correct elements for the 70 now. 608 pump,139 clutch, 904 wp pulley, 8533 crank pulley, and a 182 fan,(I know should be 5 blade 366).

All accomplished with the help of many here. Thanks to all.

**Terry M.** · July 4, 2005, 08:55 PM

Re: Regarding the fan/clutch...

Jack,
The dual bolt pattern is NOT evidence of a replacement hub, as is commonly believed. My early 1970 WP which has never been off the engine, has a dual pattern hub. Of course, there is no way to tell that without some minor disassembly, but I have been there.

**Joe L.** · July 4, 2005, 09:56 PM

Re: Regarding the fan/clutch...

Dennis and Jack-----

I don't understand how anyone mounted the 68 radiator support in a 1970. There must have been quite a few "mods" made to the support.

From the standpoint of "correctness", you want to use all the 1970 parts. However, from the perspective of functionality, you're better off with the 71 parts. The 71 waterpump is much stronger and more durable due to its 3/4" shaft. Also, using this waterpump you can use the FAR superior fan clutches used for later C3.

If you use the 71-E72 waterpump casting, GM #3991399, you can make the overall set-up look very close to the 1970 configuration, too, EXCEPT for the fan clutch. The only other visible differences would be the bolt pattern on the fan clutch hub and the bolt pattern on the fan clutch fan attachment. These things might not even be noticed.

To use the 71+ configuration, which can actually be used for any 68-70, one has to use all of the parts---water pump, pullies, fan clutch, and fan. It's the whole deal or nothing.

**Jim T.** · July 5, 2005, 12:00 PM

Re: Regarding the fan/clutch...

Terry my original 1970 July 8th late year production Corvette #608 water pump has 8 drilled and tapped holes. The casting date is L 5 9.

**Jack H.** · July 5, 2005, 12:43 PM

Re: Regarding the fan/clutch...

Discerning the difference between a '70 SB equipped with correct/original 3782608 water pump housing and '71-72 3991399 water pump housing is quite easy on the judging field. As Joe says the '399 pump has a FAT body surrounding the input shaft with LARGE fins on it while the '608 pump's nose is small and un-ribbed. All a judge has to do to detect the difference is look behind the water pump pulley and it stands out like a sore thumb...

It's kind of interesting that Chevy timed the upgrade/change over for a more sturdy, big shaft, water pump with improved side-loading strength characteristics to come on board JUST as they were cutting compression ratio and downsizing the realized HP/torque characteristics of engines...

**Dennis D.** · July 5, 2005, 04:31 PM

Re: Regarding the fan/clutch...

Joe

I'm not sure about the support. Could be 69 & up. It does have welded plates on the sides that would seem to make it fit the alum rad width. Also have the metal shroud and lower baffle. All was surrounding the 71 pieces.

It worked great for the last 33 years. I just started collecting the correct pieces and figured I'd put them on and then the entire car would be correct. Going back to donnybrook from black this fall as well. Guess I'm feeling nostalgic in my old age.

As someone mentioned, it's strange that GM" beefed up" these parts just when the power curve was coming down. Think I'll keep the 71 parts though, for when I change my mind again.(in another 3 decades, Ha)

**Joe L.** · July 5, 2005, 05:09 PM

Re: Regarding the fan/clutch...

Jack-----

As I mentioned, I wouldn't recommend this change for anyone considering entering their car for judging purposes. However, if someone wants to maintain near-original configuration for other purposes AND have the benefit of the stronger pump and the ability to use the much improved later fan clutches, then this is a way to go. I would expect that very few folks that observe one's engine compartment are going to go looking behind the waterpump pulley to see if the neck configuration of the waterpump is correct, or not.

**Joe L.** · July 5, 2005, 05:26 PM

Re: Regarding the fan/clutch...

Dennis-----

The 1968 supports have the same basic support "frame" as the later, but they have large "braces" welded to either lower side to mount on the frame horns. I suppose that these could be "hacked off" and, then, what's left might work ok for a 1969+. I couldn't say, for sure, though as there may be other differences.

The change in the waterpump configuration for 1971 was, basically, a change to improve pump durability. There's really no "performance advantage" or, even cooling advantage. Both the pre-71 and 71+ small block pumps use the same pump volute configuration and, for several years after 1971, used the same cast iron impeller (later, they went to a stamped steel type for all small block pumps). However, the 3/4" shaft pump provided much greater durability. Most small blocks from 1971-on used the 3/4" shaft and a 5/8" pilot. Corvettes and some MD/HD trucks were one of the main exceptions. They used a 3/4" shaft with a 3/4" pilot. I don't know why they did this. It doesn't make a lot of sense to me from a standardization perspective, but that's what they did.

Big block pumps always used a 3/4" shaft. So, all of the big block pumps used from 1965+ are 3/4" shaft models. For Corvettes, which always used the "short leg" style big block pump, any of the 4 CASTINGS used over the 65-74 period are functionally interchangeable. However, in 1971 the big block waterpump pilot for Corvettes changed, too, to the 3/4" pilot. So, the complete pump ASSEMBLY for 65-70 Corvetees is different than the 71-74. The only functional difference is the pilot, though.

**Jack H.** · July 5, 2005, 08:27 PM

Gotcha!

I must've read too fast, Joe. I thought you were saying one couldn't really detect the difference!

Plus, I agree--the '399 pump is the stout MONSTER that was really needed for the high horsie SB cars. Too bad they didn't go to it sooner...

For those of us who need a '399 due to judging considerations, they're not all that easy to come by. Guess I'd 'prefer' to see the early Shark guys sticking with what's factory concours 'correct' and leaving the few '399 pumps all to us....

**Joe L.** · July 6, 2005, 12:41 AM

Re: Gotcha!

Jack-----

Also, if one pays attention to the bolt circle for the fan clutch hub and the fan-to-clutch, then one doesn't even need to look for the incorrect waterpump snout configuration. If the fan clutch and the fan are incorrect as determined by these measurements, the waterpump snout will be known to be incorrect without even the need to do a close inspection.

As I mentioned, 99% of the folks that look at the installation will not recognize the discrepency in these dimensions. However, for a judge, that's really all he/she need to look at. Further inspection becomes a moot point.

The 3991399 pump castings were only used on Corvettes and, POSSIBLY, some HD truck applications in the 1971-E72 period. I don't really understand why they aren't near-impossible to find. They should be about as rare as 69-70 alternators. But, they don't seem to be that rare. One reason why there might be a scarcity of these things, though, is ME. I've been buying up every one I see for years. I just love the 3991399 casting. Don't ask me why.

**Terry M.** · July 6, 2005, 03:31 AM

Thanks Jim

My 70 has a January 29 date on the trim tag, engine assembled Jan 14, #3782608 water pump casting date: L 12 9. Looks like we are almost bookends -- I got the front, and you have the back.

70 L-46 radiator

70 L-46 radiator

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