I'm flumoxed

[flyboyjack]

Hey Folks,

it's been a long time for me,.... lost my '71 C10 Cheyenne Super in an accident and sorta quit for a while. (Should have stayed "quit").
I bought a '63 C10 long bed stepside from a collector/dealer of sorts. If he could have, he'd have lied about how much air pressure was in the tires.
Anyway, I'm now in the throes of trying my best to get this "steed" back to reliability and roadability. Both are a challenge and expensive.
Here's my dilemna: Living in southwest Florida, the outside temps as in most of the USA are sky high. Suddenly with the A/C on, the temps immediately go to 220 and stay there. At idle and even driving at 45-60 would not bring the temps down. As soon as I turned off the A/C temps came back to 190.
So I changed out the fan. Installed a Flex-a-Lite 3000cfm and cut 6 3" holes into the shroud with "flappers". This helped the temps, but the puzzling thing is that at road speeds 45-70 MPH, the temps slide up to 210-215 from 190 (A/C is on). Then when back in stop and go driving, the temps fall back to 190 or so, (A/C still on).
I currently have merely a single core. Trying one fix at a time. It seems the new fan gives me better temps, but I cannot understand why highway driving raises the temps and stop and go brings the temps back to "Normal"). Obviously there are no hills,.. it is flat Florida

Anyone got any thoughts/help?

Thanks.
Jack

[350TacoZilla]

I would try a small drive with your bypass flaps taped shut or maybe do one side at a time. you might be bypassing the fan too much at speed so while the air from grille is cooling truck the fan isn't helping it along. I haven't had great luck with aftermarket fans\shrouds so I usually scavenge something from a newer vehicle at junkyard that fits decent and go from there.

[geezer#99]

What do you have for a fan shroud?
Do you have pics of it and your engine bay?

[dmulally]

Would be good to see a pic. I had a trans cooler in front of my radiator and and heating problems. I ended up moving it to under the passenger floor with a strong fan extracting the hot air from it and it fixed my overheating dramas.

So perhaps have a feel for how hot the condenser is getting?

[flyboyjack]

Originally Posted by 350TacoZilla

I would try a small drive with your bypass flaps taped shut or maybe do one side at a time. you might be bypassing the fan too much at speed so while the air from grille is cooling truck the fan isn't helping it along. I haven't had great luck with aftermarket fans\shrouds so I usually scavenge something from a newer vehicle at junkyard that fits decent and go from there.

The temp conundrum happened before i modified the fan shroud with the pass through holes. The temps actually improved with my new "design"/fix. The shroud itself seems well built designed. It's aluminum, has about an inch and a half to two inches from back of radiator fins to the fan and is as airtight as it can possibly be. The shroud covers 100% of the radiator.

Thanks

Jack

[flyboyjack]

Originally Posted by geezer#99

What do you have for a fan shroud?
Do you have pics of it and your engine bay?

No pix. The shroud is made of welded aluminum bar and solid aluminum sheet. (1/8"). The unit is as airtight as it can possibly be made. The shroud covers the entire radiator. There is at least 12" of clearance from the back of the fan/shroud to the front of the sbc motor. I don't know if it's a combination of the higher cfm fan and/or the pass through holes I made but the temps are at least manageable now. I just can't figger out how highway cruising results in higher temps than slow city driving. (Unless the fan which is always running is actually reducing the airflow).

Thanks

Jack

[flyboyjack]

Originally Posted by dmulally

Would be good to see a pic. I had a trans cooler in front of my radiator and and heating problems. I ended up moving it to under the passenger floor with a strong fan extracting the hot air from it and it fixed my overheating dramas.

So perhaps have a feel for how hot the condenser is getting?

Nothing blocking the condenser other than the poor air openings from the factory design of the grill and hood. The A/C air feels significantly cooler now. I'll shoot the condenser with a laser to see what temps it shows.

Thanks

Jack

[geezer#99]

Could be your shroud is blocking enough air at higher speeds to make the temp climb.
Try removing it and see if that helps.

[Agv63]

Just some food for thought, how clean is the core on inside, i had a case once where tubes were blocked internally and did the same thing.
In town all good but freeway driving it kept climbing.

[MikeN]

Originally Posted by geezer#99

Could be your shroud is blocking enough air at higher speeds to make the temp climb.
Try removing it and see if that helps.

I believe this is your answer. Electric fans work great at idle, but at speed they block air from flowing through the radiator. There is a discussion about this exact issue over on chevelles.com. You might try experimenting with removing the electric fans, bolting on a simple mechanical fan, and seeing if your truck stays cool at cruising speeds.

https://www.chevelles.com/threads/co...1160281/page-3

[aerotruk63]

Are you running the Chevrolet Cool Pack as an A/C unit ?

[Wrenchbender Ret]

If you mean "single core" you are referring to the radiator size you need much more radiator. Get an aluminum radiator with a thick core.

George

[SkinnyG]

When you say immediately, do you mean like right-freaking-immediately, as in: there is no way the engine could actually be heating up that freaking fast?

If so - Is it an electric temperature gauge? Could be a resistance issue with the A/C being on, messing with the gauge.

[dagnabbitt]

Fans have not been installed backwards by any chance. That happens.