FYI, here is my thread where I have been doing all of my water temp testing....

http://forums.corvetteforum.com/c3-t...e-step-in.html

I will update it tomorrow after the Dewitts rad install and following test.

 

I'm not an expert, just giving the little knowledge I have. The 400 ia a siamese block, meaning no water passages between the cylinders. Big blocks do, allowing the coolant do more of the work

 

A copper rod is 3/8 of a inch thick, DeWitts aluminum rod is 1 inch thick so even though copper will have a higher coefficient of thermal conductivity the aluminum rod has more surface area and thats one reason they work better and yes the construction is different also.
A page from DeWitts catalog might explain it better then me.

 

.....there was a "heavy duty cooling" option that could have been ordered on '77-'79 Corvette(may have been part of a package, such as "trailer towing" which they did have) . I've seen about a dozen of these and it basically was a thick, rubber 5 inch tall lower spoiler that took the place of the smaller hard plastic chin spoiler. Don't know if it's available anywhere, but the first one I saw I swore was homemade until I had seen several more over the years.


....remember this on "highway speeds". You're engine is working much harder pulling the car along at 65mph vs 30mph. Harder working gasoline engine=more friction, more heat.

...if you think this is BS, ride a bicycle at 15mph for a half hour. Then, try like 23mph for a half hour(if you can)and see how much harder your body is working.

 

Very true, wind resistance goes up with the square of velocity- twice the speed means 4x the resistance. However, of course the original L48 350 that was in it two years ago never overheated, at 60, 70, 80, 90, etc and at a constant speed one isn't making more power than the other- that only happens when the loud pedal is further to the floor! Either this engine is generating more heat because of fuel control or timing issues, or the aluminum heads are conducting enough extra heat to exceed my cooling system capacity- and I guess I need to run some kind of test to figure out which (or confirm both) is the case.

I'll go look for that right now. I'll build one if I can't find one for sale somewhere.

 

UPDATE....

Go check my thread for my latest test.....Dewitts seemed to knock 20* off of my highway water temps..... Today was 88* and I was running 165* on a 30 mile cruise at 3000 rpms with AC on...... I'd say it helped....

 

This is depressing. We're working hard to pay off debts, so $550 for a new radiator is already out of reach. I guess we wasted our money on the new brass radiator. I'll have to try to return it, but they probably won't do better than replacing it with another new brass one.

Anyone want to buy an otherwise very nice Corvette?

 

In case anyone is interested, I wanted to follow up on this thread.

I returned my new copper/brass radiator to Advance Auto and got a refund. I explained all I had been through to the store manager and he agreed to approve a refund since I had indeed exhausted all of the obvious other avenues.

I was impressed with the scientific writeup from ajrothm and decided to follow his lead. I also returned the "heavy duty" fan clutch to O'Reillys and bought the "severe duty" one. I also ordered a new DeWitts radiator. It took two weeks (!!!) to get it, but it is a quality part. The only fitment issue I had was that the drain petcock needed a little love from the bench grinder to clear the right hand radiator support arm. While I was at it, I also ordered a new full seal set and chin spoiler from Dr. Rebuild, painted my inner fenders with Eastwood Underhood Black paint, and powder coated my core support, associated radiator and fan shroud brackets, and the hood hinges & hood prop. I also added a transmission cooler while I had the core support out.

The radiator arrived on Monday, I took Wednesday off of work to install it, and got to drive it to work and awhile afterwords for some testing today.

Here are some pictures for anyone interested:


Results:
Ambient temperatures today reached about 90*F. I had experimented with timing late last summer trying to address my overheating issue, and didn't remember where it was when I had put it up for the winter. I drove it today like it was when it was put into storage, and the difference was night & day. The temperature never exceeded 195 *F, and only exceeded 185 *F when I was following along with slow traffic. I drove for about 10 miles at 75 MPH and temperatures were stable at 183 *F. It is entirely possible that I may have some air still in the heads/block somehow, although I did drill three 1/16" holes in the brass thermostat on Wednesday to make it as easy as possible to bleed the cooling system.

After getting home from work, I measured the timing- 34* BTDC @ 3000 RPM without the vacuum advance. I took out 4* to eliminate the light detonation I had noticed under heavy throttle, and took it back out on the highway.

Ambient temperatures had dropped to 86 *F, but temps on the highway were still rock steady at 183 *F. Engine temperatures dropped slightly on the highway, so I'm confident that my original problem was insufficient cooling system capacity.

I noticed that my fan rotates several revolutions when I shut the engine off. I assume this may be related to the somewhat higher engine temperatures when I slow down, the opposite effect to what I had before (overheating on the highway, but instant cool down when speed dropped below 60 MPH). I still have a few seals left to install between the hood & the core support, and I will install them soon.

Overall, I'm very pleased with the radiator. I'm now confident enough in the cooling system that I'm ready to move ahead with my EFI swap and roller cam conversion plans, which I'll complete next year or later when our debt payoff goals are reached. For now, I can tinker with the Quadrajet carburetor, fine tune the performance & fuel economy, and enjoy driving the car.

Thanks for your help, guys!