Thread: SBC 350 running hot with AC on

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I have a 72 C10 with a SBC 350 (290 HP) running vintage air, FI tech fuel injection, 3 core aluminum radiator with full shroud and 2 ~12” electric fans. I also have a flowcool high volume/flow water pump and hi performance 160 degree thermostat. AND i also installed a spring in the lower radiator hose for good measure. All parts have less than 3500 miles on them. Timing is 15 BTDC and AF mixture is set with a target of 13:1.

Regardless of ambient temp, the truck runs at about ~175 degrees +/- 10 degrees at idle or at highway speeds. As soon as I turn on the ac, i can watch the temp gauge go up to 210+ and pegged siting at idle yesterday with the ambient temp at 80 degrees.
Looking for some advice or feedback that may be causing the temp to go off the charts with AC on. Thanks in advance.

12 in fans are useless . use a mechanical or get a Flex-A-Lite Syclone S-Blade Electric Fans 398 . i have used this fan on at least 12 builds . never used a shroud either .
condenser is adding heat with air on . make sure you have 3/8 to 1/2 in of space between condenser and radiator .
make sure your temp readings are correct. never rely on a gauge . verify first with a thermal gun .

Thanks for the info. Small correction, I am using 2 ea 14” elec fans. I’ve confirmed the temp with a thermal gun and the FItech handheld has a temp reading as well that’s within 5 degrees. Curious, What’s the purpose for the space between the condenser and radiator. Also, I use the shroud after doing research saying that the fan mounted directly to the radiator only covers ~65% of the radiator which in turns only cools 65% of the coolant in the radiator. Made sense at the time. Thanks !

Whats the amps draw of your fans????????

Why are you using a 160 degree thermostat? Thermostats do not control the heat in the radiator. They simply allow water to move from the motor to the radiator at a pre-determined temperature and 160 is far too cold for a motor to run. I always ran my stuff at 190/195 and never had a problem. Of course, I never used a fosdick electric fan system either.

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Get a 190* Tstat so your engine will run cleaner.

The over heating indicates inefficiency in heat removal. Mechanical fans often fix electric fan inefficiency.

If it's easier, you can try an oil cooler with a thermostatic bypass. The bypass is for the cold months. You can pull a lot of heat out from the oil.

Funny, Chevrolet didn't have any problems in 72 running all stock components except for EFI. I don't understand why people keep trying to reinvent the wheel.

high flow water pump = water moving too fast though system. loose it .
160 thermostat = wide open system water moving too fast through system . switch to 180 .
1 16 inch fan will move air better than 2 14's . if possible run a 16 in summit oem replacement 5 blade mechanical fan .

In ran a 190 when i initially did the motor install. Ran around 220 degrees in the fall last year. I know there are different schools of thought but I was concerned running that hot for extended period of time may be an (expensive) issue longer term. After the weather started to warn up, it was running hotter and then with the AC issue, i attempted to run the 160. Not sure what a fosdick fan is so can not comment on it.

The water high flow pump was recently put on and overall, help my initial heating problem. I’m definitely leaning towards an airflow isse. I have a new mechanical 5 blade fan i ordered from summit a year ago and should be an easy install. I’ll give it a shot. Thanks and state tuned.

My error. Maybe i’m On the wrong forum? I thought this was a hot rodding site.

Definition:
hot rod
ˈhät ˌräd/Submit
verb
gerund or present participle: hot-rodding
1.
drive a hot rod.
2.
modify (a vehicle or other device) to make it faster or more powerful.

I believe it’s 20 amps.

Amp rating on electric fans pretty much tell the story------------if the fans are only 20 amps-they are probably slowing down the air flow sorta like a windmilling propellar on an airplane----------

Originally Posted by Ricks72

The water high flow pump was recently put on and overall, help my initial heating problem. I’m definitely leaning towards an airflow isse. I have a new mechanical 5 blade fan i ordered from summit a year ago and should be an easy install. I’ll give it a shot. Thanks and state tuned.

If you do go to a mechanical fan, make sure to run a shroud and a clutch type is what I'd go with. A stock clutch fan for your truck should do the trick. I run a 4 core BBC copper radiator in my 72 K30 and have a 180* thermostat in my engine. Mine runs around 193* in the summer. I don't even have a fan shroud on it yet.

Your condenser should be in front of the radiator support and the radiator is behind it. The stock condensers had the core set ahead about an inch but the mounts bolted flat on the support. It might be worth spacing your condenser forward a bit to see if it helps.

i have ran the exact same setup on at least 10 builds . never any heat problems and believe me it would show up here in texas .