DeWitts (Yes, again!)

[Joe L.]

Re: DeWitts (Yes, again!)

Ed, Nothing ruins any driving experience like having your eyes glued to the temp gauge and living in dread of traffic slowdowns. So cool running was a top priority for my 66 427 L36 when I restored it a year ago. I'm running a Dewitt's 1249066M black finish (which is the 66 analogue to your 1239069M), aluminum GM ZL1 water pump (GM 3975928 IIRC), NOS GM 7 blade fan and severe duty clutch (Ebay listing 261925929396), OEM fan shroud w/o A/C extension, Zerex green coolant, w/water wetter as extra added insurance. The combination is simply brilliant. In all kinds of California heat, my temp gauge runs at 180 (IR gunned about that) and stays there for the duration. I don't run a front plate for max air flow but if I did it would be a C60 side mount. I've done this with two 66's, one w/an original 427 L36 and the other w/a bored and stroked monster 496, both w/the same excellent and identical results as reported about. I'm careful about my timing, keep them in good tune, and the equipment is all new. Good luck. JCH

Jim-------

The fan and clutch assembly in the referenced eBay item is EXACTLY the combination I recommended. It's a GM #88961768 fan clutch with a GM #342715 fan blade assembly. Apparently, Drew Odabasian (the owner of Corvette Stop) came to the same conclusion as me (or, he read one of my many previous posts on the subject here). Note that he does not disclose the part numbers of the components because he doesn't want folks to put that together themselves. However, I've disclosed them.

By the way, Drew Odabasian is the very guy that once-upon-a-time in Cupertino, CA kicked my NOS parts collection obsession into "high gear" where it's remained ever since.

[Jim H.]

Re: DeWitts (Yes, again!)

Jim-------

The fan and clutch assembly in the referenced eBay item is EXACTLY the combination I recommended. It's a GM #88961768 fan clutch with a GM #342715 fan blade assembly. Apparently, Drew Odabasian (the owner of Corvette Stop) came to the same conclusion as me (or, he read one of my many previous posts on the subject here). Note that he does not disclose the part numbers of the components because he doesn't want folks to put that together themselves. However, I've disclosed them.

By the way, Drew Odabasian is the very guy that once-upon-a-time in Cupertino, CA kicked my NOS parts collection obsession into "high gear" where it's remained ever since.

Joe, Thank you for that feedback. My empirical experience confirms your analysis absolutely. Your knowledge of such interchanges is essential to stay w/in the OEM parts universe while incorporating effective enhancing upgrades - my preferred approach.

Regards. JCH

[Patrick T.]

Re: DeWitts (Yes, again!)

Patrick, sounds like you got their "restoration" radiator. Yes?

Ed

Yep, that's the one.

[Mark E.]

Re: DeWitts (Yes, again!)

Mark------
If you want to keep the original fan, you're going to have to stick with one of the pre-1971 fan clutches. A GM #3916141 is about as good as you can do.

If low speed cooling is your top priority, then follow the advice I gave in the post you referenced.

Thanks Joe!

[Mark E.]

Re: DeWitts (Yes, again!)

This thread inspired me to check my fan and clutch-

I thought 1970 and older cars used a 3" fan bolt circle and 1971+ cars used 3 1/4" fan bolt circle. Is this correct?

Yet my late June 1970 car has a 3 1/4" fan bolt circle. When I aquired the car in 1990 it had an original looking 7-blade fan with the extended tips used on 454 AC cars, and an aftermarket fan clutch.

Is it likely the factory used the 1971 fan/clutch design on this car? Or more likely this was changed in the field at some time?

Maybe I should squint and see if there's a date on the fan...

Thanks again guys!

[Joe L.]

Re: DeWitts (Yes, again!)

This thread inspired me to check my fan and clutch-

I thought 1970 and older cars used a 3" fan bolt circle and 1971+ cars used 3 1/4" fan bolt circle. Is this correct?

Yet my late June 1970 car has a 3 1/4" fan bolt circle. When I aquired the car in 1990 it had an original looking 7-blade fan with the extended tips used on 454 AC cars, and an aftermarket fan clutch.

Is it likely the factory used the 1971 fan/clutch design on this car? Or more likely this was changed in the field at some time?

Maybe I should squint and see if there's a date on the fan...

Thanks again guys!

Mark------


Yes, that's correct; pre-1970 fans used a 3" bolt circle and 1971+ used 3-1/4" bolt circle.

There were 3 different "spike-tipped" fans (big block with C-60).

GM #3969926 and 3993889 were used for 1970 and have 3" bolt circle

GM #3992095 was used for 1971-73 and has 3-1/4" bolt circle

[Mark E.]

Re: DeWitts (Yes, again!)

Well, I guess the good news is that this fan is compatible with Joe's favorite clutch- GM #88961768.

[Edward B.]

Re: DeWitts (Yes, again!)

I know this thread is old, but I wanted to give you guys an update on what's happened.

I FINALLY got a Dewitts 1239069M radiator from Ernie (Wilcox Corvette) a few months ago. He was having a 20 percent off sale and I couldn't pass that up! I also got a new reproduction (date coded) expansion tank, a new Mr Gasket 180 degree thermostat and all new hoses. I also got the recommended 50/50 antifreeze Dewitts recommended. It's 50 percent coolant and 50 percent demineralized water. (Yes, I could have gone down to the water store and got the same thing and mixed it myself, but it would have cost about the same, so I just got the 50/50 premix.)

Anyway, most of Saturday was spent removing the old radiator and installing the new one. That in itself was a MAJOR pain. However, after getting it all installed and test driving the car, the temperature STILL went up to 210 degrees! Needless to say, I wasn't a happy camper. BUT. After examining the shroud, I discovered a lot of gaps between it and the radiator. Apparently, after 50 years, it had become so warped and sagging at the bottom, it wasn't doing its job. There was a two inch gap at the bottom, about a 1 inch gap at the top on the passenger's side, and both sides had about a quarter inch gap as well.

Not wanting to say die at this point, for testing purposes, I duct taped the heck out of the shroud and radiator, and now there's NO gaps and the car barely hits the first marker on the gauge! Even in stop and go traffic. Using my IR temperature gun, I'm getting temps around 177 to 180 all over the engine. The black duct tape looks like crap, but for now, it works, so needless to say, I'll be buying a new shroud in the near future!

All in all, I LOVE the dewitts radiator. It's a well engineered, well manufactured product. The date code on the expansion tank isn't as nice as I hoped it would be though. It doesn't look much like an original. But since I don't "show" my car, it'll be fine.

Hope this helps the next guy that has cooling problems!

And by the way, I have a feeling that my original radiator may be just fine, but with all the gaps from the warped shroud, THAT may have been my problem all along! I'll keep it as a spare.

Ed

[William F.]

Re: DeWitts (Yes, again!)

Only things about all this, I don't know if C3 big blocks came with aluminum radiators(did they??
),but c2's came with copper/brass radiators, not aluminum. The DeWitts "Direct Fit" is aluminum, I believe. They also make original type brass/ copper ones.

[Joe L.]

Re: DeWitts (Yes, again!)

Only things about all this, I don't know if C3 big blocks came with aluminum radiators(did they??
),but c2's came with copper/brass radiators, not aluminum. The DeWitts "Direct Fit" is aluminum, I believe. They also make original type brass/ copper ones.

William------

The only C3 big blocks that were ever originally equipped with an aluminum radiator were 1968-71 with L-88, ZL-1, and LS-6 and also equipped with 4 speed transmission. All other 68-71 big blocks (and, all 1972-74) were originally equipped with copper/brass radiators.

The DeWitts "Direct Fit" is not a reproduction of the 1968-71 big block aluminum radiator, though. That radiator, GM #3007436, is also reproduced by DeWitts but it's quite a bit more expensive than the "Direct Fit". The latter is, basically, an aluminum copy of the copper/brass GM #3019190/3018571. When painted, it appears very similar to the original big block copper/brass radiator. However, this radiator has a cooling capacity greater than ANY radiator ever originally installed in a Corvette from 1953 to 2017.

[Jim D.]

Re: DeWitts (Yes, again!)

DeWitt's also offers a "HP" version of their "Direct Fit" radiators that offers substantially more cooling capacity over the standard "Direct Fit".

[William F.]

Re: DeWitts (Yes, again!)

Is the number for the GM gasket that goes between intake manifold and thermostat housing/water outlet , the gasket that doesn't require any sealer, same for big block as small block? Also, what's the pn for Mr. Gasket Robert Shaw type thermostat for a '67 big block?

[Joe L.]

Re: DeWitts (Yes, again!)

Is the number for the GM gasket that goes between intake manifold and thermostat housing/water outlet , the gasket that doesn't require any sealer, same for big block as small block? Also, what's the pn for Mr. Gasket Robert Shaw type thermostat for a '67 big block?

William------


Yes, the gasket is the same for both big block and small block-----GM #10105135.

Mr. Gasket Robertshaw-style thermostat of 180 degrees (which is original and what I recommend) is #4364.

[William F.]

Re: DeWitts (Yes, again!)

Will the DeWitts aluminum copy of the original GM copper /brass bb radiator "judge?"

[Joe L.]

Re: DeWitts (Yes, again!)

Will the DeWitts aluminum copy of the original GM copper /brass bb radiator "judge?"

William------


It's certainly detectable. The most obvious difference is that the core is welded to the side tanks and not soldered. However, I've seen at least one Top Flight 1969 that had the DeWitts Direct Fit aluminum radiator. I do not know what deduction it might have suffered.