I had the exact same problem with same setup on my '32. Took the shroud off, solved problem. Shroud won't let enough air pass thru at speed.

 

Go here and read about cooling: http://www.crankshaftcoalition.com/wiki/Bulletproof_cooling_system

Two core rad....Big block......no!

 

2 core aluminum rad made for big block but I have a smallblock lol.
I read somewhere to install rubber flaps that open at highway speeds!

 

Also make sure that lower hose is not callapsing at speed. That needs to have a coil spring in it to keep it open.
Usually overheating on highway is not enough cooling system, overheating in driveway, not enough air flow. Might need 3 row radiator

 

I cut 4 holes in my rad shroud & installed rubber flaps, no help. But, what works 4 1 person won't work for anutter. Is that a 16in puller fan?

 

yes spal HP puller 2025 CFM.
the cooling sytem is good rad is more than big enough.
Keep in mind the system wasnt an issue with factory shroud and mechanical fan!

 

If the timing is a little slow it will make an engine run hotter on the highway. Won't cost anything to double check it.

John L

 

chatted with the local radiator shop owner while the wife and i had breakfast in a local diner.
He stated that my problem is common with the custom shrouds.
they cool good under 30 mph or so but fail to cool at anything higher.
he said additional holes need to be made in the shroud and thin rubber flaps will need to be placed over holes.
by thin he ment .010 to no more than 1/32"thick rubber so incoming air will open them causing flow through the radiator and suck closed at lower speed.

 

If the timing is a little slow it will make an engine run hotter on the highway. Won't cost anything to double check it.

John L

Timing was checked and rechecked .
I even had the car on the sun diagnostic machine (remember those?)
all plugs firing good and timing is perfect.
I even had the distributor (new unilite) put on a distributor machine to check it.

 

since it only overheats at highway speeds, it could be that more air is flowing around/under/over the radiator than thru it.

 

H Dawg, thank you for your service haven't seen you around much or for a while. You probably know what i am going to say but here it is anyway, loose the electric fan go back to a good stock style mechanical or a real good aftermarket fan With a shroud. JMO and if you want to continue to use the pulley set-up you have on it now which i really like. just machine the water-pump pulley so the mechanical fan is recessed in the pulley and then all should be good. I have been there done that Dawg ain: either way good to see you again. If you need pics of exactly what i done on my pulleys let me know . :thumbup:


Cole
imp:

 

That fan / shroud setup is not allowing ample air flow at speed. Looking at it it is probably covering about 30% of the radiator. this will cause air to go around instead of through. Sealing the top of the radiator to the support may help a little. On the highway that shroud is doing more harm than good. On the highway you don't need a fan as natural airflow should be more than enough.
You said it worked fine with the stock fan and shroud, this tells the whole story.
If you have a manual switch on the fan try turning it off on the highway and see if it helps, the fan can also impede air flow.

 

the mfg suggest I kick out the bottom for a 1/2 to 1.0" gap to allow air to flow.
if it works I should place a few 2" holes with 1/32 rubber flaps to correct issue.
if angling doesnt work they offered to refund my money for the shroud/fan assy.

 

BS! you dont know what your talking about!
the panel actually directs more air into the radiator.
mFg write up:
This panel was originally plastic and installed on the big block a/c cars. GM knew that the air was being re-introduced to the front of the radiator when idling. At speed the pressure from air coming under the core support was working against the flow of air through the radiator, so this panel was designed. The GM panel only goes as far as the core support.

We wanted to force ALL of the air from the grille through the radiator, so ours goes all the way up to the backside of the spoiler (or the valance). It has a divider at the core support to finish off the seal. It will protect youir lower pulleys from picking up debris and flinging it all over your motor. You wont stir up as much dust when you are cruising because all of the air off the radiator is directed to the rear of your engine.
without it it is runnin hotter.

cut the holes and installed the rubber flaps.
car stays at 180 degrees now either in city traffic of on the Hiway.
Ya learn something new everyday!
even a know it all learns aswell sometimes!

 

87 Firebird, I wondered what that rubber? piece was below my front spoiler. spoiler should have given me a clue, I thought that the factory just put it on to make it look lower and was told it was to create a low pressure area at speed.

 

Can you post up a picture of the holes/flaps you installed? I'm having a similar issue. This might be the fix.

Thanks! Scott

 

I got my shroud working perfectly now.
never gets near 200!
both in traffic and going 65-75 on the highway
I used a 2 1/2 inch knockout to make the holes

now to clean everything up.

 

It is really sad that you spend good money for something and then have to re-engineer it to make it useable.

 

The quick and easy way for next time is to throw the shroud away. That electric fan without a shroud will be adequate. And as always make sure your timing and fuel is correct. If your tuneup is correct you can use a much smaller fan and be fine as long as you have otherwise good airflow. The fan is only for very low viehicle speeds in which case your engine should not be putting out much heat- if it is tuned properly.

 

It is really sad that you spend good money for something and then have to re-engineer it to make it useable.

these days its always that way!

 

I have twin Spal fans on my 59
They have the openings with the rubber flaps.
Car still runs a bit warm, but i am not bothered by
anything under 210 - 215 at cruise.

My fans are set to come on at 225 and off at 215.
(454HO and a 5-spd)(BeCool 2 row crossflow---kinda small but nothing
larger will fit in that car.

2 row radiator with 1 inch tubes are plenty for a BB
assuming the radiator is sized correctly.

My 66 Elky with an old SBC 307 also has an aluminum
2 row radiator--again 1 inch tube--but it is a downflow.
Have a set of twin FlexiLites that will cool the car right down
when it gets up to 205.
At cruise, they do not come on and even with the AC enough
air is flowing that the pressure switch on the AC does not always
turn the fans on----unless I come to a stop and air quits moving.

But that engine is virtually stock.
But hey, smogger 307 and a 5-spd gets me better than 25 mpg

 

Dawg, what material is the shroud made out of? Aluminum or stainless? Could you make those flaps out of a chunk of the same material and attach them to the shroud with hinges? It may look cleaner than rubber? Just a thought.

 

aluminum and its being done.

 

I hope you'll post up a pic of the updated "flaps" once installed. I've found this thread very, very interesting. My radiator mfr used to provide these type flaps on all their shrouds. They quit doing so shortly before I purchased. I'm looking forward to seeing the cleaner, all metal style flaps.

PatM

 

already got em cut now to get some mini hinges.