C2 Aluminum vs. Brass Radiator

[Rich G.]

I have a 66 L79 which has the incorrect brass repro radiator. I've had this car since september. I notice now that I'm using the heater that the coolant temp goes down from an indicated 200 to 180 when I put the heat on. Does this indicate that the radiator is not being the best of heat exchangers? I have heard both; that the brass is ok, and read another post reporting 20 degree cooler results all around after changing to aluminum. BTW, I have been through all the temp sender stuff and I know the car is not running too hot and I believe the radiator is clean, altough I did not do it myself. Just curious about the effect the heater has on the coolant temp. and whether there is a concensus that the aluminum does a better job of exchanging heat.

Thanks

Rich Giannotti

[Jack H.]

Re: C2 Aluminum vs. Brass Radiator

Much in the archieves on this subject. Basically, brass is MORE efficient as a conductor or heat than aluminum (co-varies with electrical conductivity, think of copper vs. aluminum wiring in your house....).

The 'trick' is brass is very soft compared to aluminum and given a cubic inch silhouette constraint, you can't scale down the packing density of brass to the extent you can aluminum. Therefore, aluminum wins in an 'apples to apples' packing density situation where it can use MUCH thinner walled tubes and a higher count of fins per linear inch of cooling tube.

When you turn on the heater, you're pulling BTU's out of the coolant system IN ADDITION to those naturally expelled through the radiator. You've essentially added a second, albeit tiny, radiator to the system to exhaust heat into the passenger compartment.

[Joe L.]

Re: C2 Aluminum vs. Brass Radiator

Rich-----

Brass is a better conductor of heat than aluminum. However, the design and configuration of radiator cores which aluminum allows for makes for a much more efficient radiator. That's one of the reasons that practically all modern vehicles use aluminum radiators. So, the bottom line is that an original Corvette aluminum radiator (e.g. 63-72 GM #3155316) is a lot more efficient than the replacement copper-brass radiator which is similarly configured for fitment purposes.

An automotive heater core is, basically, just a small radiator that radiates heat into the car's interior rather than into the "great outdoors" as does the cooling system's primary radiator. So, when the heater is turned on, some of the cooling system's heat is radiated into the cabin producing some degree of reduction in the coolant temperature over what the primary radiator can achieve. This is especially true if the primary radiator is "marginal" and cannot control the cooling system temperature at the thermostat-regulated temp level. In fact, a little known "trick" for dealing with a car overheating in high ambient temps and low speed operation is to turn the heater on. Of course, that's just about the last thing that someone wants to do under such conditions, but it has been known to "save the day" every now and then.

Anyway, I recommend the use of an aluminum replacement radiator for ANY Corvette that was originally so-equipped. You can get increased cooling capacity from a copper-brass radiator, but you can't do it with a copper-brass radiator configured like the original aluminum unit. To do this, you need to change radiator support, shroud, hoses, and other parts to convert to a different design copper brass radiator. Few folks want to get into all this for a variety of reasons.

[Joe C.]

Re: C2 Aluminum vs. Brass Radiator

Rich:

Obviously very true what Jack and Joe said about the additional heat exchanger, only necessary with high ambient temps. I recall an experience in Death Valley, about 20 years ago @ 115 degrees outside temperature, where 3 buddies and I were on a cross country Cannonball Run with a 360 Dodge Maxivan. Damn thing started to get too hot, so we removed the engine cover, opened all the windows, and turned the heater on "full blast" to keep from boiling over. It did the trick, but my pal John didn't see the humor in the fact that his broken nose swelled to about twice the size after the ordeal. I have NEVER heard of heater operation making a difference at the temp gauge. What ambient temp are we talking about? Has the temp gauge/sender unit been modified?

Joe

[Rich G.]

Re: C2 Aluminum vs. Brass Radiator

Joe...

That sounds like a real fun trip. I recently read an article about the "Canonball".

First, thanks to all of you for comments.

Second, Joe , I have a standard temp gage set up and I have calibrated the gauge using resistors and a graph of resistance vs. temp that Jack sent to me, so I know the gauge is pretty close. The sender is a LIC "special" with a 10 ohm resistor in series supposedly to "calibrate" it. There's a lot about this in the archives. I got another sender from Jack, but haven't installed it yet.(sorry Jack!) In any case, yesterday the ambient temp was a balmy 30F and after driving a few miles at 65 the temp settled on 200. Turning the heater on showed a drop of 10-20 degrees at the same speed. I have noticed the same in warm weather except that the gauge shows 220 then drops 10-20 when the heater goes on. I would think (and agree with you) that if the thermostat and rest of the cooling system are working right, the heater shouldn't make a noticeable difference. BTW, when my gauge says 220, a themometer in the tank says 180, which is why I started checking the calibration and got the sender from Jack. I guess I can't draw any conclusions about accuracy until I try the new sender, but this issue of the heater making a difference led me to ask the question.

I would think that the cooling without the heater on when the ambient is 30F should be sufficient, so that the additional cooling provided by the heater core would be compensated by the thermostat. I only have this car since September and have put about 700 miles on it with no real trouble. The previous owner said it has a 180 degree thermostat, but I haven't verified that. I think I see an aluminum radiator in my future anyway.

Thanks again for the comments

Rich Giannotti

[Joe C.]

Re: C2 Aluminum vs. Brass Radiator

Rich:

I am only guessing here, and this situation sounds very interesting, but do you notice any significant fluctuations in your gauge under any other circumstances (prolonged idling, A/C on or off, different ambient temps., etc.)?

I can tell you, that I calibrated my gauge/sender circuit to read a true 180 degrees @ a measured 180 degrees thermostat temp by using a t******* resistor in series with the sender-to-gauge signal lead. This provides very stable steady state readings, with normal gauge sensitivity. I have an aluminum DeWitts radiator installed in my 1965 engine bay, and the only time that temp gauge starts to climb, is during prolonged periods of STATIONARY idling in very hot weather (approx. 85 deg +, amb.)

This might be a STRETCH, but it IS possible that the power draw of the blower motor might cause a sufficient voltage drop to affect your temp gauge. Your battery. and/or regulator might be marginal.

Another good source of help might be www.vintageresearch.com

Joe

[Jack H.]

Interesting speculation!

With heater on, fan has several speeds and CAN present an appreciable electrical load (branch circuit is typically fused at 30-35A).... If everything remains constant in the temp guage circuit AND the effective voltage supply rail to the dash drops, then current flowing through the temp guage, to the sender and ultimately to ground is going to FALL in lock-step with the drop in supply voltage (indicated temp would be reduced).

This is pretty easy to check out without having to outfit a voltmeter.... IF it's a case of unstable supply voltage, then changing the setting of the heater blower motor should generate fluxuation in reported temp (the faster the blower motor, the higher the current consumption, the greater the drop in B+ and the more reduction in temp indication). Next, you should be able to trigger the idiosyncrasy by turning the heater off, and turning on another equally high current consuming load like the headlights....

[Rich G.]

Re: Interesting speculation!

Thanks for the suggestions. I don't think it is electrical as the temp doesn't go down right away, and I do get a small drop with only the heater vents open and no fan, in other words with just "slipstream" air blowing on the heater. The electrical system seems ok, in fact the car has the bigger and incorrect alternator on it. (63 amp?) The gauge changes slowly. around town in the winter it stays around 180-190 indicated. In hwy driving it rises to 200-210. I'm pretty sure the fan clutch is ok as I had it checked by a guy I trust. In any case it is easy to measure the system voltage under these conditions and I will do that.

I'm inclined to believe that my radiator is not doing the best job of exchanging heat, whether due to age or condition. The motor is a 30 over rebuild by the previous owner and has about 2000 miles on it now. It runs very well, has good oil pressure and uses no oil.

Thanks again for all the suggestions. I'll keep the board posted when and if I find anything interesting.

Rich Giannotti