Thicker versus thinner radiator core 4

[JoshMalks]

The issue is the radiator in an antique automobile (1936 Cord). The size of the core is restricted by the grille shape, and air inflow is restricted by the hood shape. The original engineers opted for a 4" thick core to try to provide sufficient cooling capacity.

The car runs fine in 90% of use. Long hills or very slow traffic on hot days test its limits. A query by a member of our club to Harrison Radiator (GM) in the 1950s brought the response that the 4" core was needed to provide cooling at high speeds, but that its thickness reduced air flow thru it at lower speeds. They said that a 3" core would solve the cooling problem at low and medium speeds, but might be marginal at high speeds (over 70 mph).

Does this agree with current thought? Thanks. (And while we still drive our cars at highway speeds, we rarely exceed 70 )

 

[brokenot]

I'd keep the original thick core, but have it disassembled and cleaned really well. Any scale deposited on the walls of the tubing will greatly affect how much heat is dissipated. I'd also spend a couple of hours with a fin comb while the radiator was out to straighten any bent fins.

With the radiator up to par, (and the scale and rust flushed out of the rest of the cooling system as well), the problem *should* be solved. If it isn't, installing an electric fan to aid in the airflow at lower speeds would be a simple fix. My boss has a Lincoln Zephyr with a flathead V-12 that had the same problems you're experiencing. After a thorough cleaning of the radiator, fabrication of a tight-fitting shroud to pull all of the fan air through the core, etc. etc., the car still would run a little warm in stop and go traffic.

An auxiliary fan was mounted, (out of sight in front of the radiator), and wired to a thermostatically controlled switch and relay. Works like a charm, the only caveats being that the car is no longer "original".....and also that the additional electrical load from the fan meant that the charging system had to be upgraded as well. (Newer vehicles have 100 amp and up alternators for a reason!)

At lower speeds the fan really helps. It pushes a lot of air through the radiator, and expels a lot of the heat that's normally just trapped under the hood.

 

[Newmanite]

A set of twin thermo fans should cure your low speed hot day probs.Along with good quality coolant not that nasty green stuff from B.P. Wetter water is a very good product but its not that cheap.Then again neither is a cracked head

 

[patprimmer]

The so called nasty green stuff, being ethylene glycol will increase the boiling point of the coolant and thereby raise the cooling efficiency due to the greater temperature difference between the air and the coolant.

It can rot older type seals and hoses if used in to high a concentration, so care should be taken to ensure the correct rubber is used for these parts. With this, the originality of the car can be maintained.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[IRstuff]

If you're not planning on driving in sub-zero temperatures, you could switch to propylene glycol, which is much more environmentally friendly.

Ethylene glycol tends to break down into noxious subproducts in hot environments, particularly if you get it to boil.

TTFN

FAQ731-376

 

[JoshMalks]

Thanks, guys. But my friends and I have been fooling with (and driving) our Cords for many decades. We keep the rad clean, use Water Wetter, and add little electric fans.

My question still, if anyone can answer, relates to the core thickness. 4" is pretty thick, and the Harrison engineers back in the '50s thought that this was done to keep the car cool at high speeds, but actually impeded cooling --- due to difficulty in getting air thru it --- at low speeds. They said a 3" core might do just the opposite. Any of you kind folks have thoughts on that?

Original radiator, incidentally, was by Jamestown. It's not quite cellular, but definitely not fin-and-tube.

 

[IRstuff]

The simple question to ask is whether the car had a reputation for overheating at low speeds when it was new. Since most cars spend the bulk of their time at low speeds, one would hardly think that the design would have optimized only for high speeds, particularly in a passenger car.

TTFN

FAQ731-376

 

[JoshMalks]

Yes, IRstuff, the Cord always ran warm at low speeds. No pressure on the radiator originally, altho I do run a 4-pound pressure cap on it now. The car was intended as a high speed (for those days) touring sedan. (Cords held the AAA-certified American stock car speed record at 107.66mph for 17 years.) Still, I know they did not intend it to run warm at low speeds. We know that the basic problem is insufficient airflow, and some of us are working with this too. But my question still remains --- is it true that a thinner core will improve low-speed cooling because airflow thru it is greater than thru a thicker core?

Thanks again, all.

 

[FoMoCoMoFo]

I think not. there will be some small increase in air flow but a decrease in area for heat transfer and volume of coolant flow. fan and shroud design are indicated if it cools well at higher speeds.

 

[IRstuff]

The reduction in thickness increases air flow and decreases heat transfer area, although, there is should be a slight uptick in net performance. If you're going to that level of modification, a better approach would be a more efficient radiator to begin with, more fins, or whatever.

TTFN

FAQ731-376

 

[MikeHalloran]

It's probably too late to ask the Harrison guys what they assumed or knew about the problem, or how much analysis or experiment they might have conducted before answering the question. If question and answer were not exchanged in writing, they probably just did a little 'bench racing', as is going on here.

My take is that you'd have to gain a lot of airflow to offset giving up 1/4 of the surface area.

There are two ways to find out: A custom thinner 'old school' radiator that is not authentic and may be of no use whatsoever, or CFD analysis. Both will cost you money that is better spent on beer.

Me, I'd save the authentic parts for the next owner, and use a modern core and auxiliary fans.




Mike Halloran
Pembroke Pines, FL, USA

 

[Fabrico]

Regardless of airflow, any part of the core that is not doing its job transferring heat, will act as a bypass for coolant. More is not always better.

 

[JoshMalks]

Interesting point, Fabrico. If the fins at the three-inch-deep point of core depth have warmed to a temp equilibrium with the water coming down, the rearmost inch might not be "doing its job". Is that what you're suggsting?

 

[MikeHalloran]

I think Fabrico is suggesting that it's difficult to balance the coolant flows through all the tubes.



Mike Halloran
Pembroke Pines, FL, USA

 

[JoshMalks]

Why would that be? If the top tank is full of water, and the floor of the tank is larger than the top of the core, would not water have to flow thru all the tubes? (Assuming uniform states of cleanliness.) Just askin'.

 

[patprimmer]

Position of inlet and outlet pipe can be critical to flow balance. Internal baffles may also necessary to prevent to much flow in some areas via an easy path.

The radiator would work more effectively if the header tank could be divided so that the water passed through the back half, then the front half in a double pass or even a triple pass if you want the entry and exit at top and bottom respectively.

A more efficient core and a more efficient fan are the best ideas to date. Poor low speed cooling is most easily solved with a bigger engine driven fan.

If it is engine driven in the original style but with more or bigger blades or turned at higher speed, or the blades have more pitch, it might even pass unnoticed, especially with the higher speed or bigger pitch method

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MikeHalloran]

Yeah, you'd think so, but nobody told the coolant that it has to split equally among all the tubes, and it doesn't.

For one thing, my experience with a small number of radiators suggests that the rate at which the crud plates out on the tubes is temperature dependent, so the rear (I think) rows clog first.



Mike Halloran
Pembroke Pines, FL, USA

 

[JoshMalks]

Mike, I will be careful to so instruct my coolant before my next trip.

And Pat, the Cord has two inlet pipes to the top of the radiator (from the two sides of the V-8) but just one large outlet (to the input of the water pump) from the bottom tank. The owner of my Cord 50 years ago thought that the water was being pulled to the outlet side, so he split the top tank (side to side) with a divider inside. Don't know if that did any good. It has long since been converted back to stock, and there are no records.

You're talking about forcing the water to go down the back tubes, then up the middle tubes, then down the front tubes. I read once that much of the benefit of multi-pass configurations related to the increased turbulence. Any thoughts on that?

And thanks, guys, for putting up with this thread this long. You are all being very helpful.

Your discussion

 

[Fabrico]

Interesting point, Fabrico. If the fins at the three-inch-deep point of core depth have warmed to a temp equilibrium with the water coming down, the rearmost inch might not be "doing its job". Is that what you're suggsting?

Yes, but that's only part of the problem. That one third of the radiator that's not accomplishing anything is letting one third of the coolant bypass the cooling process. A 4" core could virtually let half of the hot coolant circulate from the engine right back into the engine.

 

[daubery]

Reduce radiator depth (thickness), & increase fin density slightly. Work on a louver angle of around 27 - 30 degrees - with louver at >=90% of fin height.

Radiators are cross-flow devices & it can be shown that under many flow conditions the air exit temperatures & water temperatures coincide - after which no further cooling will occur in that section of the radiator (physics under a temperature-cross condition).

Typically, unless you have a very healthy fan pushing the air through a radiator, anything over 3 rows is a waste of metal - better to re-design the entire radiator a little more efficiently.

Why do you think Japanese radiators are only 16mm thick?

Des Aubery...
(adTherm Technology)