Thread: Aluminum shroud heating issue

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Ok I have fabricated a shroud for my radiator with a spal puller fan.I am very limited with space so originally I had the fan mounted on the radiator.The shroud is barely 3/4" of an inch with the fan now mounted to that.When I went down to Reno for Hot August nights(about 35 miles)the temp went up to about 205 when I was driving on the freeway.When I get into slow moving traffic it drops to 195 or less.I am thinking that when I am doing a faster speed the air flow now gets backed up against the shroud with no where to go.What do you guys think,the only other thing I can think of is it is leaning out a little.Any ideas

Could be lean, or could be a cooling issue. What stat are you running in it?? Finding a balance between a good shroud, but one that doesn't restrict airflow at highway speeds is tough!!! Did you try kicking the fan on manually on the highway to see if it would cool????

Its a 185 stat and the fan is on at 195.I have seen on some shrouds where they have flaps that looks like they will open when at higher speed.Seems to be happening at speeds above 60 or so.

Originally Posted by Blow by

Its a 185 stat and the fan is on at 195.I have seen on some shrouds where they have flaps that looks like they will open when at higher speed.Seems to be happening at speeds above 60 or so.

Sounds like too much restriction when you're going down the highway...Never have seen a shroud with flaps, but I have put louvers in a few to let the air go through the radiator easier. Air will always follow the path of least resistance, it it's easier to go around the radiator then thru it, that's where it will go..... When space limitations come in, hard to put the cooling system in the perfect configuration!

If you are saying that the distance from the back side of the radiator to the shroud surface is 3/4", then your thoughts about that being too small are correct. Going down the road, the air is probably piling up and the only air flow is essentially the diameter of the fan hole. The flaps you refer to are usually a rubber flap that are simply pop riveted to the fan shroud and covering holes cut in the shroud. You might call some pro like Griffin Radiator and ask how much space they recommend between the radiator core and the shroud.

Another thought is perhaps your fan is helping to limit the flow at highway speeds. Can you switch your fan off on the road to test?

mike in tucson

The problem here is that at speed, the fan cannot freewheel as fast as it needs to to allow full air flow. The electric motor acts as a sort of brake. Even if you turn the fan off, I don't think it can freewheel fast enough.

The shroud on my electric fan has two rubber flaps near the bottom. If the fan is pulling, they are sucked shut. If the air "stacks up" at speed, they open and relieve the pressure. They have to be one-way, though.

It's kind of hard to see, so I outlined it. There is one on each side.

I am going to try the fan off idea as it is an easy one to check.This coming winter I will put some flaps in it as I also think that it is a situation where the air is backing up and has no where to go.The whole idea of this shroud was to see if it did make any great differance as it had always intrigued me eventhough I new it would be a tight fit.

Originally Posted by Henry Rifle

.......The shroud on my electric fan has two rubber flaps near the bottom. If the fan is pulling, they are sucked shut. If the air "stacks up" at speed, they open and relieve the pressure. They have to be one-way, though.

It's kind of hard to see, so I outlined it. There is one on each side.

Yeah, when Cooling Components first came out with their fan/shroud combo they didn't have those flaps. A few years ago I noticed they added the flaps and asked them what they were for, and they said to allow more air through at higher speeds.

My fan/shroud has two flaps like Jack's, but I think on some of the larger shrouds I have seen 4 flaps, two at the top and two on the bottom.

I like the Cooling Components fan/shroud combo because it cools better at low speeds and in traffic. I do think I ran a little cooler on the highway when I just had my 16" Spal with no shroud.

I just pre-ordered one of their (Cooling Components) new fans from Walker at the Nats in Louisville. It has a larger (17") fan and a larger shroud, so I hope that allows a bit more air through on the highway. The larger fan is also not as deep, so it will help those who have clearance problems. It draws a bit more current and requires a larger relay, but that thing sure seemed to move a lot of air when I was comparing it at the show.

A little cooler might give you more comfort but 205 is not bad. My 34normally runs 200 - 205. Heavy traffic will take it to 210/215. Hiway driving in the boonies might get me 190. Different story in my 57 though, rarely gets over 195, usually sits about 180, except in real heavy slow traffic, then it climbs to 210. 57 has stock radiator and stock engine turned fan, 34 has 10 inch pusher and 16 inch puller. You don't want to run too low or your combustion will be inefficient, especially with today's lousy gas.

Another thing you can try is a spoiler under the front bumper or under the radiator. This causes a low pressure area so the hot exhaust from the radiator has a place to go.

I had an 89 T-Bird Super Coupe and hit a tire tread on the highway one time, it ripped off the spoiler however I stopped and picked it up (luckily). But untill I re-installed it, the car would run much hotter.

I ripped the spoiler off my Dodge diesel truck last winter on a snow drift on the highway and the same thing happened. So these spoilers are good for something besides looks.

I like the louvre idea as from what I have seen so far that shroud is not actually doing that much.Had an idea it wouldn't when I made it but wanted to try anyway.Like Mopar34 said the temps aren't to excesssive so at the moment I am not to concerned.Good little winter project once the snow flies.

Originally Posted by Henry Rifle

The problem here is that at speed, the fan cannot freewheel as fast as it needs to to allow full air flow. The electric motor acts as a sort of brake. Even if you turn the fan off, I don't think it can freewheel fast enough......

I agree with Jack. But also what temp do you want to run at? I don't see anything wrong with 205 F. At 15 psig 50/50 antifreeze and water boils at 265 F.

It is a case of highway air usage inefficiency though and that would drive me nuts too. The relief valves (flaps) will probably get you there.

Kitz

Here's a link to Ron Davis Radiators - I happened to recall seeing this dual fan radiator with flaps....

http://www.rondavisradiators.com/staggerd-dual-f&s.jpg

I've seen a bunch with louvers too.... I'd do one or the other.

JB

The reason that they use flaps instead of louvers is that the air takes the path of least resistance. If the louver path is easier than the air going thru the radiator, then the louvers will flow until the louver path equalizes with the radiator path. Therefore, the louvers can help at some times and hurt a tad at other times. The flaps only help since they are a diode in the system. Louvers are just like an air gap between the shroud and radiator....a leak.

Louvers look cooler than flaps...the cool look may help cool the car....???

mike in tucson

I had never seen the flaps until I ordered a new aluminum radiator for my '39 Dodge. However, I can see the concept.


Don