C3 Correct Radiator???

[Norm C.]

This may be a question for Joe Lucia or Chuch Berge, but welcome any & all experience!!! I have an older friend who refuses to enter the computer age, and has stumped me with his question.

He has a small block 72 4-spd with air. Owned for several years, is the 2nd owner & believes it to be un-molested. Radiator has a small leak & he is on the fence if he should repair or re-core. He asked me if he goes new, what to order. It's very possible I'm reading the JG & GM parts book wrong.... but the JG calls for a 26in copper core for 72 4spd/Air. Yet the GM parts book only refers to the 27.5in which is what he has. It also makes the distinction between 4spd vs TH (Turbo Hydro Auto) by showing W/Oil Cooler,,, which makes sense, & of course he would not need. Doubt the owner will ever have the car judged, but he doesn't want to depart from being correct.

Questions? 1. While the JG says 26in copper, is there a history of this application having the 27.5in copper as well? 2.Is there any history of a change or modification during the 71-72 production for radiators. 3. Is there any experience with judges seeing differences than what is listed in the 70-72 JM? On a side note, not important to the owner,,,,,but JG also refers to a tab sometimes seen on 71-72's with a 2 letter code,,, yet GM book shows those not being used until 73???? Thanks to all for your help!!!!

[Chuck S.]

Re: C3 Correct Radiator???

There aren't very many cases where I would believe the JG over GM parts books, but this may be one.

According to Tom DeWitt's site and previous posts in the archives, the 26" core is used for small block radiator with THM or AC, and the 27.5" core is a big block engine radiator. The original radiator for my 70 base engine w/AC measures 26.25" from tank flange to tank flange.

Your friend's probably should have come with a 26" core, but if push came to shove a 27.5" might have found its way onto his car in St. Louis. Now he has a choice...he can put it back like it should have been, or he can put it back like it is.

http://www.dewitts.com/pages/productdetail.asp?ProdID=263

OR: http://www.dewitts.com/pages/product...asp?ProdID=262

[Terry M.]

Re: C3 Correct Radiator???

"JG also refers to a tab sometimes seen on 71-72's with a 2 letter code,,, yet GM book shows those not being used until 73?"

I have a Corvette parts book dated 1972 with a chart that refers to those letters as a means of ordering the correct replacement radiator. That chart is lacking in earlier dated parts books, at least the ones I have, but I would not use that lack of a chart to deduce that the earlier radiators didn't have those tags. I suspect the chart was published someplace else earlier.

I a not sure what GM book you are looking at, but I can assure you all 1968-1972 OEM radiators had the tag with the broadcast code. A year or so ago there was a survey done on this board as a means of filling in some of the missing codes. Quite a few members responded with information from the radiator tags on 1968 and newer Corvettes.

The guys on the line didn't measure the radiator -- nor did they look for the holes for the M40 transmission -- they looked for those two letters on the tag to insure they were installing the correct radiator because the inspector checked that tag also.

[Norm C.]

Re: C3 Correct Radiator???

Thanks Chuck,,, I kind of felt the same way...EXCEPT.....When you ck the parts book,,,,can you see a part/radiator number for a small block 4spd with air??? Each of the 26's are shown for the THD W/Oil Cooler.

We know the original 4-spd radiators didn't come with the oil cooler,,, although I've seen those used as replacements with the oil cooler connections capped off. Parts book shows # 3018802 = 69-72 W/TH = 26 W/Oil Cooler; #3007436 =70-72 350 W/HD 4-spd H/Per = 21"

The only other explanation I can think of (assuming the JG is correct) is the GM parts book I have has an inadvertent deletion of the part/radiator # for the one in question. Mine is 53-82 effective 12/83 with several AIM pics. BTW.. AIM doesn't solve the mystery either. Anyone else have other possibilities???

[Chuck S.]

How To Back Into The Right Answer...

The parts book I have (Corvette Parts Book, 1953-1972) is a publishers compilation of GM parts books...imperfect but a good reference.

If I look through the Group 1 listing for radiators (1.219), I find as you did, no direct listing for small block air-conditioned cars in 70-72...no listing at ALL. What I do find is a single listing for the 69 small block w/CAC (exc. THM, 427)...PN 3018803. Was there any reason to change this radiator after 69...ummm, no don't think so.

So then I plug 3018803 into the NCRS Archive search feature, I come up with the following thread: https://www.ncrs.org/forum/archive11.cgi?review=65873 . Joe can help us even when he's out of town. My conclusion is the listing for the 3018803 listing was never updated after 69 to extend the application to newer cars...an editorial error.

[Chuck S.]

More...

During the 69-70 model years, the broadcast code that Terry describes was MK followed by a small 9 for the 3018803 radiator. I don't know that this broadcast code remained the same through 72 (broadcast codes did not change every year like they do now). The broadcast code tag should be about half way down the passenger side tank on the engine side of the radiator.

[Joe L.]

Re: C3 Correct Radiator???

Norm-----

The correct radiator for a 1972 with small block, 4 speed, and C-60 is GM #3018803. This is the 26" core, copper brass radiator and it has no integral oil cooler. The GM #3018803 was discontinued from SERVICE many moons ago and replaced, for SERVICE, by the GM #3018802 which is exactly the same radiator except that it does have the oil cooler (unused, of course, when this radiator is used to SERVICE 4 speed applications).

For 1972, the small block copper brass radiator had the 26" core. The big block had the 27-1/2" core. However, ther is another notable difference between the two radiators which easily identifies them----the 26" core radiator has a filler neck on the top of the right side tank. The 27-1/2", 69-72 big block radiator has no integral filler cap, at all-----it's designed for use with an external supply tank.

If the radiator happens to have a 27-1/2" core AND a filler neck on the right side tank, then the radiator is the 1973 radiator used for all 1973 applications. Could said radiator have been used for late 72's? I suppose it's possible, but I have no reason to believe that was done. Also, I doubt it. The 73 radiator was coded "MC".

As Terry mentioned, the radiator broadcast code tags were used prior to 1973. However, they did not always appear in the parts catalogs prior to that time.

[Norm C.]

Thank You Chuck & Joe

Chuck & Joe,,, You have solved the mystery!!!

So the GM books should have continued to show PN 3018803 which is the same except the right side tank doesn't have the oil cooler. Interesting that the replacement PN was an earlier number than the original. I knew Tom DeWitts was where to send the owner, just couldn't figure out which core.

Joe or Terry from earlier in this thread..... do you know what the broadcast codes were for the 71-72 radiators,,, Were the codes the same for both sizes? Or was the MC code the first broadcast code for radiators? My book starts with the MC code in 73 but then doesn't include the core widths. Also Joe, the JG refers to the broadcast codes being available inconsistantly for the 70-72's.... out of curiosity, do you know why they weren't used consistantly......OMG..I HAVE passed over to the dark side!!!

[Joe L.]

Re: Thank You Chuck & Joe

Norm-----

I don't know why the broadcast codes were not used consistently. I have seen some radiators that didn't have them. However, what I don't know is if they ALWAYS didn't have them or if they lost their somewhere along the way. Also, I think that there may have neem another paper label somewhere on the radiators which had the broadcast code so that it could be easily discerned by assemblers. This label may have been in an inconspicuous location with the radiator installed in the car or it might have been removed subsequent to installation.

The GM #3018802 and 3018803 radiators were released at the same time for the 1969 model year. However, after PRODUCTION use of the radiators ended in 1972, GMSPO probably felt that there was no need to keep both radiators available in SERVICE----the 3018802 (the one with oil cooler) could be used to SERVICE applications which originally used either radiator. The exact same thing occurred for the 69-72 big block copper brass radiator----the once-available unit without oil cooler was discontinued in favor of the unit with oil cooler to SERVICE all applications.

The 1969-72 code for the small block radiator with oil cooler (3018802) was "MK9". I'm not sure what the code was for the 3018803.

[Chuck S.]

Re: Thank You Chuck & Joe

After Joe's reminder about the 27.5" core big block radiator not having a filler neck in the tank, I realize your friend can't make his big block radiator correct for judging by a simple core change.

Even if it's the later 73 copper radiator with the filler neck in the tank, changing the core to 26" won't really help on correctness if the 73 tanks are configured different.

Your friend has an interesting decision to make...put it back like it has been with a 27.5" core, or make it like it was supposed to be by springing for another MK9 radiator if he can find one. You have deinitely passed over...bitten by restoration vampires.

[Terry M.]

Re: Thank You Chuck & Joe

Sorry Norm, but the only broadcast code I am sure of is the MK9 Joe already mentioned – it is the one on my car. I hope the soon to be released 1970-72 TIM&JG will contain the rest of them. You might try emailing Tom Dewitte for the codes -- he was the main researcher on the thread I mentioned earlier. I believe his desire was to make the tags available in reproduction to go with his reproduction cores.