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Too much air pressure under the hood?

5K views 25 replies 13 participants last post by  rslifkin 
#1 ·
How can I find out if the engine compartment of my truck ('57 Chevy truck)becomes "pressurized", meaning all the air that comes in through the grill does not have an easy enough exit to create a strong air flow through the rad. If warm air stays too long, does not move enough out of the engine compartment, then new, fresh air cannot flow freely through the rad, and bam! overheating...
Is there an easy (and cheap!) way to find out?
Thanks
 
#7 ·
I don't see how that could happen



All the air coming through the radiator from the fan is simply escaping from under the truck. The only way the engine compartment could become pressurized is if you sealed off the bottom of the engine compartment.
This is not the source of your overheating problem. Don't know what cooling system setup you have but the overheating issue is likely fan/shroud/radiator/water pump/thermostat related.
 
#8 ·
Thanks for all the comments!
'57 Chevy Suburban, '93 TBI350ci, all stock, stock mechanical fan, stock rad, stock fan shroud, th700R4, all out of a Buick Roadmaster SW. So the engine compartment is pretty full, that is why I was wondering, if the air is flowing out freely, since a completely stock set up should be fine.
The truck is not dramatically overheating, just sometimes, when towing, the temp seems to move up a bit, and I have never had a chance to tow in warm weather, yet... So I am just trying to think a bit, before I start spending money...
 
#11 ·
How is the fan positioned in the shroud. Should be about half the blade covered. Sounds like not enough air flow or too small a radiator. If it is a clutch fan make sure it is locking up when the engine is warm.
The fan usually has no impact on cooling once you are moving at 30mph or so as the forced air will be more than enough to cool. This is assuming all the iar is going through the radiator and not around it.
If it only does it under tow load most likely the radiator may be a bit to small.
 
#13 ·
factory engine oil cooler.

The factory installed engine oil coolers on some of the bigger trucks. A friend owns a wrecking yard and when the semi trailer mounted crusher shows up we sometimes help him and anything on the Red X painted crusher cars is free to us, I pulled a cooler systen from a Chevy Uhaul truck. still in a box in the shop.
 
#15 ·
there is plenty of room around the bottom of the motor for air flow, especially compared to new cars
i get a lot of movement in the top skin of my hood from 80 to 100mph in my 58
though i suspect that is more from air moving over the hood and not under the hood

 
#18 ·
It is funny how my engine compartment looks much fuller than yours. I have the battery in the stock location, and the stock GM fan shroud does look big! My engine seems also to be further back than yours, I do not have much space between firewall and distributor (my truck has a Camaro front clip).
But now that you mention it, my hood also moves at speed, it is usually pushed down, mostly since I have mounted a sunvisor: the air gets stuck in front of the windshield and does not where to go, I guess!
 
#17 ·
I found out the hard way that my cowl induction hood on my 81 Camaro was causing the air to stall in front my radiator. Only ran hot on the highway. I installed a home made air dam and the problem went away. The cowl wasn't sealed to the intake so the high pressure air from the bottom of the windshield was pushing down in to the engine bay and at highway speeds, because of the aerodynamics of the vehicle, the air couldn't escape by moving down and out so airflow across the radiator was limited. The air dam creates a lower pressure behind the radiator allowing for better air flow. Might not be your problem but it's worth mentioning. Someone else reading this might be pulling their hair out too!
 
#20 ·
Packaging, yes, I guess that's it. I have the big stock AC compressor on top of the engine, the big factory fan shroud... I have not spent any time trying to make my engine bay look nice, it looks like what the factory would have made. I did not need a recess for the HEI, though, using ''77 Camaro front clip and engine mounts. Yours look very clean and organized, but I am not really interested in that in my cars!
But that is why I was wondering if the air was to flow freely through in the first palce... Time for the towing package rad!
 

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#23 ·
Thermostat

Hey Wave, Good idea to use all the Roadmaster parts possible in your swap, makes replacement parts easy to get. Cool air cleaner housing. Combo has a rat rod look it. You should post some photos of the truck. If I were in your shoes, I'd put a 160 degree thermostat in it, original is 195 degree. All of the later model engines are designed to run real hot, with temperatures soaring up to 220-230 while towing being considered acceptable. If you switch to a 160 t-stat, you may be able to get it to level out in the 190's while towing. You can try it for less than $10. If it gets real cold where you live, you can put the 195 t-stat back in during the winter for the cost of a gasket.
Nolan
 
#25 ·
Hey Wave, Good idea to use all the Roadmaster parts possible in your swap, makes replacement parts easy to get. Cool air cleaner housing. Combo has a rat rod look it. You should post some photos of the truck. If I were in your shoes, I'd put a 160 degree thermostat in it, original is 195 degree. All of the later model engines are designed to run real hot, with temperatures soaring up to 220-230 while towing being considered acceptable. If you switch to a 160 t-stat, you may be able to get it to level out in the 190's while towing. You can try it for less than $10. If it gets real cold where you live, you can put the 195 t-stat back in during the winter for the cost of a gasket.
Nolan
Yes, good point, I have a lower temp T-stat on my other car, but forgot to try that on the burb!
My air cleaner housing is a mid '50s Cadillac.
 
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