DeWitts (Yes, again!)

[Steve M.]

Re: DeWitts (Yes, again!)

Have you tried running without a thermostat? Checked the fan clutch?

[Edward B.]

Re: DeWitts (Yes, again!)

Have you tried running without a thermostat? Checked the fan clutch?

Yes, late last summer I pulled the thermostat just to see if it would help. While it took longer to heat up, it still went to 220-230 as I drove around town. The clutch is new, and was replaced for this purpose, but it didn't help either.

On the open highway, it's not so bad. It still gets hot, but not 220-230. Only when driving in stop and go traffic does it get REALLY hot. This indicates not enough air being pulled in, and since everything else has been replaced, I guess the only thing left is the radiator.

Ed

[Joe L.]

Re: DeWitts (Yes, again!)

Yes, late last summer I pulled the thermostat just to see if it would help. While it took longer to heat up, it still went to 220-230 as I drove around town. The clutch is new, and was replaced for this purpose, but it didn't help either.

On the open highway, it's not so bad. It still gets hot, but not 220-230. Only when driving in stop and go traffic does it get REALLY hot. This indicates not enough air being pulled in, and since everything else has been replaced, I guess the only thing left is the radiator.

Ed

Ed------


Want to improve idle and low speed cooling? Very simple. Install fan clutch GM #88961768, aka Delco #15-4950. You will also have to install a 1971+ fan blade assembly. In this regard, I recommend a GM #342715 if you can find one or, otherwise, a GM #469580. It's even possible that the 88961768 now has dual bolt patterns for both the 3" and 3-1/4" bolt circle fans. I doubt it, but it's possible. So, if you decide to go this route, check the clutch before you buy the fan.

Also, if you are using the 1965-70 style waterpump with 5/8" pilot, you MUST use the 3/4"-to-5/8" adapter bushing usually supplied with the fan clutch (or, which you can get at good hardware stores if it's not supplied with the clutch).

This is the absolute BEST fan clutch EVER used on a Corvette. PERIOD. Yes, the installation is not going to appear stock for any 1969 and it's a bit noisy. But, if you want the best idle and low speed cooling, this is the way to go. PERIOD. Never leave home without one. I've got a lifetime supply of its predecessor part numbers (basically, exactly the same as the 88961768). That's because I NEVER want to be without one. Ever. PERIOD.

[Edward B.]

Re: DeWitts (Yes, again!)

Joe I checked ebay and the fan clutch is still available at a reasonable price. The fan (new) is not!! I may be able to find a used one locally. I know a few guys that have a lot of C3 parts.

Thanks again
Ed

[Joe L.]

Re: DeWitts (Yes, again!)

Joe I checked ebay and the fan clutch is still available at a reasonable price. The fan (new) is not!! I may be able to find a used one locally. I know a few guys that have a lot of C3 parts.

Thanks again
Ed

Ed-------


Make sure the fan clutch you get has the DUAL pattern hub. Otherwise, you will have to convert to the 71+ waterpump and 71+ pulley.

I think that the GM #342715 is discontinued. However, I believe the GM #469580 is still available.

[Edward B.]

Re: DeWitts (Yes, again!)

Yes, the clutch on ebay has both patterns, so I think that should work okay. The 342715 is available NOS, but at $400 I pass. The 469580 is still available and at just over $100 it's a much better deal.

Ed

[Mark E.]

Re: DeWitts (Yes, again!)

Ed,

Here's a data point for you: I have a 1970 LS5 with AC and had the original radiator re-cored. On warm days in Texas (I've driven it in 95 degree weather a few times) it stays below 210 degrees (mid-point on the gauge). I know you don't have an original radiator to re-core, but if you want an original look, a good reproduction copper/brass radiator might perform fine.

Another thought- When it's 115-118 degrees outside, leave the big block in the garage and take the minivan! I can't imagine expecting any pre-84 Corvette to keep you and itself cool in those extreme conditions.

EDIT: I also made sure my water pump, thermostat and fan clutch are working properly, AND spent a lot of time installing new seals between the radiator support, radiator and shroud.

[Edward B.]

Re: DeWitts (Yes, again!)

Another thought- When it's 115-118 degrees outside, leave the big block in the garage and take the minivan! I can't imagine expecting any pre-84 Corvette to keep you and itself cool in those extreme conditions.

Not only that, but it's a black car with a black interior!!! Yes, I sweat like a pig!

Ed

[Mark E.]

Re: DeWitts (Yes, again!)

Joe,

I'm very interested in your opinion about fan clutches:

"Install fan clutch GM #88961768, aka Delco #15-4950. You will also have to install a 1971+ fan blade assembly. In this regard, I recommend a GM #342715 if you can find one or, otherwise, a GM #469580. It's even possible that the 88961768 now has dual bolt patterns for both the 3" and 3-1/4" bolt circle fans."

Which clutch would you recommend for a 1970 LS5 AC car if I want to keep its original fan (I don't have its PN in front of me, but its the fan with the unique tips that extend past the shroud opening a bit)? The car has its original water pump (rebuilt, of course), but an aftermarket clutch that came with it when purchased used in 1990 (it works but has some lateral run-out, so it's on my list to replace).

An original looking clutch is a plus, but I'm more interested in low speed cooling.

Thank you!

[Joe L.]

Re: DeWitts (Yes, again!)

Joe,

I'm very interested in your opinion about fan clutches:

"Install fan clutch GM #88961768, aka Delco #15-4950. You will also have to install a 1971+ fan blade assembly. In this regard, I recommend a GM #342715 if you can find one or, otherwise, a GM #469580. It's even possible that the 88961768 now has dual bolt patterns for both the 3" and 3-1/4" bolt circle fans."

Which clutch would you recommend for a 1970 LS5 AC car if I want to keep its original fan (I don't have its PN in front of me, but its the fan with the unique tips that extend past the shroud opening a bit)? The car has its original water pump (rebuilt, of course), but an aftermarket clutch that came with it when purchased used in 1990 (it works but has some lateral run-out, so it's on my list to replace).

An original looking clutch is a plus, but I'm more interested in low speed cooling.

Thank you!

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.

[Patrick T.]

Re: DeWitts (Yes, again!)

I remember back in 2009, I was getting my 67 327/350 ready for Flight Judging at the Gettysburg Regional. The car still had its original radiator in it but it was pretty ratty and had repairs to it. I was only going to do this restoration one time so I got a DeWitts detailed, dated and painted radiator. With the shipping charge, the total $$$ came to around $800. Glad I did it.

[Edward B.]

Re: DeWitts (Yes, again!)

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

Ed

[Jim T.]

Re: DeWitts (Yes, again!)

You mentioned running hot around town in summer, cars with a vacuum advance canister in place with direct full time vacuum and the correct vacuum advance canister not functioning can run hot around town, especially sitting at multiple stop lights.

[Martin M.]

Re: DeWitts (Yes, again!)

Here's an additional diagnostic aid: for 2 years before we moved to Las Vegas i noticed the engine temp creeping up on the gauge, this on a '63 300hp original car. The radiator was not original, and not aluminum, but for 15 years kept the temp at or below 180, never over. I had a lot of other things to do (Move!), so I decided to wait until we did move.

We ran the car a bit here and observed the same results. I hit it with my temp gun and it confirmed the temp was correct. So I decided that DeWitt's was the answer, but I made 1 last move, and installed a Robertshaw 180 degree thermostat I bought at NAPA in Maynard, MA before we left the area. Voila, temp back to normal, overheating gone. I can sit in rush hour traffic on a 100 degree day, and the temp is 180.

What I am saying here is that a 50 year old Vette with an original water pump, replacement radiator, correct shroud, correct radiator cap etc will run 180 all day in 100 degree heat with out a murmur. And has been running this way for 15 years! After all, these cars did not overheat when they were built.

Just Sayin'

[Jim H.]

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