Packard Forum Index » Post-War (1946-54)

Here are some references on radiator thickness vs performance.

Basically, larger is better but thicker is not always better. Thinner is better if but if you can make it larger, then do it. We usually don't have room to make it larger and keep it thin.

Pay attention to the comments on flow rate in the following youtube video. Higher flow rate is better even if the temperature drop is lower across the radiator. More energy is taken out of the system with higher flow rate. When we increase the thickness of the radiator, we slow the flow rate unless we change the pump.


youtube.com/watch?v=Ldfuzy_JJUo

And here is more from another site:

cliveyboy.com/2012/11/how-to-improve-your-cooling-system/

Radiator

Finally the radiator. This is the most misunderstood part of the cooling system and the one which has the biggest effect should you get it wrong.

Fitting a poorly designed/modified radiator would mean having to greatly increase the air and water flow just to compensate for its inefficiency.

How do we know what is an efficient radiator?

If you fitted two different radiators to your car each of these would try to lose ALL the excess heat (heat load) across its core. In order to do this the radiators need to find a big enough temperature difference between the water and air. Each radiator would allow the water temperature to keep rising until it achieved that temperature difference.

When the radiator has found that temperature difference and is able to lose all the excess heat this is known as its "steady state" condition. A good efficient radiator is able to start losing heat at lower air temperatures and so stabilise (reach steady state) at a lower temperature.

A poor radiator might need such a high temperature to achieve a steady state that it boils before that temperature is reached.

A good efficient radiator is one that can start transferring heat at lower temperatures.

So how do you build an efficient radiator?

An efficient radiator is one that can expose enough water to the air so all the heat is lost at a low temperature.

So if you increase the surface area of the radiator by adding more cores etc you increase efficiency? Not necessarily.

Remember what we said - if you change one thing it always affects one or more other things. In the case of adding a third core you affect both the water and the air. Firstly the water instead of travelling through two cores is now split between three - this means the water slows down. (Remember increased flow = increased cooling).

If the water slows down too much you get "laminar flow", where hot water clings to the tube walls almost stopping heat transfer. N.B. Going to a smaller tube size when adding an additional row is one way to keep the flow rate up, but they are more prone to blocking up.

The air as it travels through the radiator will be warmed up by the first core, warmed up even more by the second core, so by the time it gets to the third core you are trying to cool it with hot air. The temperature difference between the water and air will be much lower. That could mean either little heat transfer or the radiator could start to raise the water temperature to try and increase that difference.

If there is a high enough air flow through the radiator, fitting an extra core may help. But remember, if you add extra cores to a radiator not only do you slow the water down but cool more of that water with hot air. If you are fitting an extra core to a radiator, both air and water flow should be increased for maximum benefit.

A better way is to increase the radiators frontal area either by making it bigger or increasing the number of tubes in the rows. The water flow rate through the tubes will drop (same as adding an extra core) but you have the advantage that more water is being exposed to the coolest air hitting the front of the radiator. Therefore the air will be cooler when it reaches the second row. This helps maintain the temperature difference between the cooling air and the water. The bigger the difference the more efficient the radiator can cool.

A bigger radiator or more tubes per row exposes more water to the coolest air. Again, if you increase the surface area of a radiator, both air and water flow should be increased for maximum benefit.

In conclusion

This should now have covered the major points that affect a cooling system. Hopefully you now understand in more depth how your cooling system works, and so can make an informed decision as to whether that very expensive up rated aluminium radiator with extra cores is actually what you need.

You may also be interested to read an article I wrote on aluminium radiators and how they compare to copper/brass ones.

Good Morning again Joe...I did neglect to mention that we also added a fan shroud and a higher CFM Fan to our system. I really do not believe that the larger radiator is your problem. All of your comments mirror our experience and the distributor and vacuum advance were the final difference.

I am also active with Model A Fords and we routinely put larger radiators and fan shrouds on them to run them in the desert. If everything else is right, it always works.

We did also change from a Autolite distributor to a Delco distributor as the advance is internal in the Delco and with the Autolite, the entire distributor has to turn and can be impaired by the plug wires.

I have also read that some cars begin with the timing a little advanced from the 6 degrees that the book calls for with modern fuels...I am no expert, I am just relating what happened with our Packard.

Deluxe Canuck, up in Canada also added a shroud to his 1949 and reported that his cooled down after the shroud was added.

One question...What temperature is the return water coming into the radiator and what is the temperature of the output water returning to the radiator? Ernie

Hi Ernie,

Your inputs are appreciated. Per my comment above, the input temperature vs the outlet temperature are not necessarily a guideline as to how much energy is taken out of the system. If you watch the youtube video, you will see that:

Higher flow rate is better even if the temperature drop is lower across the radiator. More energy is taken out of the system with higher flow rate.

There have been comments on this and other sites that warn about removing the thermostat. They post that the increased flow from the unrestricted outlet allows the coolant to pass too quickly through the radiator core to be cooled sufficiently. This seems to me to be counter to your statements and references. I don't know, but I am curious. Thanks - JWL

That is a good point. Obviously, we don't want to remove the thermostat since there are many other benefits to having the controlled block temperature that the thermostat affords (like removing oil impurities and such)

Most of us as kids have experimented with pulling out the thermostat and found better cooling as a result.
I have never tried to see if there is a difference in cooling at idle vs cruising without the thermostat. There may be.

In my case, I am talking about a radiator that is now thicker than the original thinner one and trying to determine why my cooling at low rpm's is affected so negatively. I have a large spread between cooling at cruising speeds and idle. As I mentioned above, I had the problem even on a 35 degree morning.

Obviously, we can build shrouds or add auxiliary fans but as restorers of these great cars, I think we want to get them back to original without patches if possible.

It is hard for me to think that when the car was new in 1949, the owners needed to deal with a thermal runaway situation at idle (especially in Pennsylvania where I live). Since I have had the engine rebuilt and changed all of the cooling components, there is not much left but the radiator and the fluid flow rate analysis to try to get it back to original performance. (And Ernie's suggestion about the vacuum advance)

In any case, I still need the dimensions and specs for the original 419500 core. If anyone can get them, please let me know

Perhaps some info about actual temps involved would help.
Is there actual boiling? Are we looking just at a guage indication that may or may not be correct?
The new handheld thermometers are inexpensive and can
give an idea of actual conditions.
Actual ignition timing at idle should be pretty advanced
compared to static timing, due to the vacuum advance, slow timing certainly allow them to heat up pretty fast.
Also, a fairly small difference in clearance at the water pump rotor could make a BIG difference in flow at idle, does the heating only happen when actually idling, or does
increasing RPMs help any?

Joe, maybe somewhere in this long thread you wrote that everything had been checked and found to be okay. If not, maybe your idle high temps are caused by something as simple as a bad distributor vacuum chamber that coincidentally failed when the re-cored radiator was installed. Easy enough to check. The problem you are describing sure takes the fun out of motoring. JWL

Yes, I am using the handheld scanner for temperature. The engine creeps up to about 220 deg F and I shut it off before it goes higher. So I don't know if will boil over or not.

The vacuum advance comments are well taken. I need to still check that out per Ernie's input.


I need to do more testing at increasing rpm's when idling.

Thank you for the excellent comments!

Just to confirm that the timing is supposed to be set with the vacuum advance disconnected and plugged off? I believe this is the right way to achieve the correct "static" timing? And then once the vacuum advance is hooked up again, it automatically should advance, even at idle?

Raise engine IDLE speed 200 rpm.
That should solve the problem.

Also advance timing or at least check timing at idle speed.

Original factory specs (OF ANY ENGINE MADE AT ANY TIME BY ANY MFG'ER) usualy indicate a rather slow idle speed than what is practicle for REAL WORLD operation.

Raise idle speed to at least 500 rpm. ESPECIALY if it has AC.