79 Z-28 5.7 still overheating issues with alum radiator/electric fans

biker

Veteran Member
Gold Member
Dec 7, 2014
5,309
Canada
1975RS - great news, but ... how close is the mechanical fan to the rad core?

Question 2 - pardon me for asking, but with the mechanical fan installed along with the electrics and their slotted mounting frame (as seen in the photos you've posted) what is it really doing other than blowing air on the block?

Reason I ask is that when I first started breaking in my rebuilt 350, I had the mechanical fan installed without the shroud. As such, it was not pulling air through the rad. So long as the water was moving everything was fine with the rad cap off. As soon as the engine stalled - the coolant flashed to steam and shot straight out of the open rad hole. Talk about projectile vomiting! 🤮

All I'm really trying to demonstrate here is that a mechanical fan spaced back from the core without a shroud is probably not pulling any air through the rad, not causing the designed temperature drop across the rad and may be only cooling the block directly.

FWIW ...
Agreed, but maybe the mech fan is creating some sort of condition with the hood closed, that is allowing the electric fans to pull just enough more air through the rad
 

sandlapper

Veteran Member
Oct 9, 2020
1,653
SE CSA
Dunno if the following has any scientific validity, but I follow a rule of thumb I learned somewhere --- with pump-driven fan clutch --- fan blade should be positioned approx half in & half out of shroud opening. I've made no formal investigation, but seems OEMs are about same --- perhaps that rule came from observing OEMs, dunno.

I've no doubt that along the way, some poor fellows have incorrectly mated a reverse cool fan & clutch with a standard rotation pump --- or vice versa --- stuff happens.
 

G72Zed

Veteran Member
Sep 8, 2015
4,241
Canada
Dunno if the following has any scientific validity, but I follow a rule of thumb I learned somewhere --- with pump-driven fan clutch --- fan blade should be positioned approx half in & half out of shroud opening. I've made no formal investigation, but seems OEMs are about same --- perhaps that rule came from observing OEMs, dunno.

Your rule of thumb is bang on the money sandlapper.

It’s the same way I see it as well.

And when you have racers spending 1K on just a couple of little plastic solid mount fans with different blade counts/pitch and weight to get an edge, that positioning is a top priority, And go to great lengths to get this right.

Another golden nugget !!!!
 

Bandit723

Veteran Member
Oct 1, 2016
4,376
Waupaca WI
Dunno if the following has any scientific validity, but I follow a rule of thumb I learned somewhere --- with pump-driven fan clutch --- fan blade should be positioned approx half in & half out of shroud opening. I've made no formal investigation, but seems OEMs are about same --- perhaps that rule came from observing OEMs, dunno.

I've no doubt that along the way, some poor fellows have incorrectly mated a reverse cool fan & clutch with a standard rotation pump --- or vice versa --- stuff happens.
I will give you that not having a rad shroud makes a diff. Not sure i buy into having a gen1 pump, fan and engine turning in the right direction is the problem.
 

Bandit723

Veteran Member
Oct 1, 2016
4,376
Waupaca WI
Your rule of thumb is bang on the money sandlapper.

It’s the same way I see it as well.

And when you have racers spending 1K on just a couple of little plastic solid mount fans with different blade counts/pitch and weight to get an edge, that positioning is a top priority, And go to great lengths to get this right.

Another golden nugget !!!!
Dude the OP is not a racer. Food for thought
 

G72Zed

Veteran Member
Sep 8, 2015
4,241
Canada
Dude the OP is not a racer. Food for thought

Dude, the OP needs all the “food for thought” as he’s starving!!!!

24 pages trying to figure out how to cool an original 1979 Z28 350 sbc with 175hp, figured the OP needs all the help he can get or read!!

I make 3X the HP with my 72 Camaro with a 350 sbc, and I need to block 1/2 my rad in spring and summer.
Iron head wit almost 11:1 compression and 34* idle timing and I need to warm it up before going for a ride.

It’s amazing what a properly tuned engine can tolerate.
 

sandlapper

Veteran Member
Oct 9, 2020
1,653
SE CSA
I will give you that not having a rad shroud makes a diff. Not sure i buy into having a gen1 pump, fan and engine turning in the right direction is the problem.
I have yet to indicate that's THE problem. I suggest that mismatch could be a real problem for some fellows and, of course, that might include our poster as well. If there's a mismatch, it cannot cool adequately. There are a whole host of possibilities --- foremost is possibility of scale and/or muck inside radiator and/or block and/or heads. Entrained air is another. Clean surfaces transfer heat far more efficiently than do dirty ones. I'm not there to see-test poster's issue. I don't KNOW his root cause; I do suggest possibilities. I'm here to try to help others.
 

Orkin71ss

New Member
Nov 20, 2022
5
It runs great. Thanks for reply.
71 SS camaro 350 mild cam aluminum heads and lifters. I had some issues with overheating. Do you have a fan shroud? Mine has no AC and I found that you can run a hose from the ac outlet on the manifold to the rear of the manifold, which will help circulate more water through the block. I still need an electric fan and I should get it connected with a thermostat, but for now a manual on and off switch. It brings it down to 180 within minutes.
 

1975RS

Veteran Member
Oct 19, 2018
170
p
71 SS camaro 350 mild cam aluminum heads and lifters. I had some issues with overheating. Do you have a fan shroud? Mine has no AC and I found that you can run a hose from the ac outlet on the manifold to the rear of the manifold, which will help circulate more water through the block. I still need an electric fan and I should get it connected with a thermostat, but for now a manual on and off switch. It brings it down to 180 within minutes.
putting the shroud back on it soon
 




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