The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - BBC temp creeps at idle; how did factory do it?

jumpsoffrock · 06-16-2021, 11:01 PM

How'd these trucks stay cool from the factory with AC?

My factory 402 truck does not have AC from factory. I took it upon myself to find a 4 core brass radiator out of a GM vehicle, this rad is almost identical to the factory 4-core for these trucks. Radiator shop said it was in "fantastic condition", they were rather surprised. Didn't need any work.

Thermostat is 180º

I use a mechanical gauge with sender placed at thermo housing.

Fan was upgraded to a giant 5-blade 20.5" metal fan out of a 1972 Buick riviera that had AC. Everything looks factory.(According to internet non-AC '72 Riviera's had a four blade fan). This fan fits in the factory shroud perfect, partially in/out, it's like they were made for eachother.

I also grabbed a 7-blade steel fan from a guy who has these trucks all over his yard.

Both fans have a nice pitch to the blades--these things were made to move air.

After installing and testing both fans on near 100º days, they had similar results and one issue:
They will NOT keep engine sustained at any temp at idle(7-800rpm). It always creeps up, haven't let it go too high because the creep is slow and it would take forever(good thing).
If at a stand still I bump the gas pedal to 1500 rpm it cools right back down in less than a minute at that engine speed.

After extended 3000rpm driving today(98º) I pulled over immediately and the engine was at 190º. I sat at idle for a solid 10 minutes and it crept up to 210. At this point I put it in granny gear and drove 5mph at 1500rpm, in a minute it was down to 190º and stayed there without issue.

As for as I'm concerned this is simply an issue of lack of air movement through the radiator at idle.

If my truck creeps 30º or more on a 98º day and it doesn't even have AC, how did these trucks with this engine and factory AC keep cool? Did GM just not expect anyone to sit at idle for extended periods?

I see guys in work trucks sitting at idle with AC blasting for half an hour today, I can't imagine people didn't do this 50 years ago. I can't imagine GM simply "overlooked" sitting at idle with AC on like nobody does that.

Did these trucks slowly overheat from the factory?

06-16-2021, 11:01 PM	#1
jumpsoffrock Registered User Join Date: Apr 2014 Location: California Posts: 926	BBC temp creeps at idle; how did factory do it? How'd these trucks stay cool from the factory with AC? My factory 402 truck does not have AC from factory. I took it upon myself to find a 4 core brass radiator out of a GM vehicle, this rad is almost identical to the factory 4-core for these trucks. Radiator shop said it was in "fantastic condition", they were rather surprised. Didn't need any work. Thermostat is 180º I use a mechanical gauge with sender placed at thermo housing. Fan was upgraded to a giant 5-blade 20.5" metal fan out of a 1972 Buick riviera that had AC. Everything looks factory.(According to internet non-AC '72 Riviera's had a four blade fan). This fan fits in the factory shroud perfect, partially in/out, it's like they were made for eachother. I also grabbed a 7-blade steel fan from a guy who has these trucks all over his yard. Both fans have a nice pitch to the blades--these things were made to move air. After installing and testing both fans on near 100º days, they had similar results and one issue: They will NOT keep engine sustained at any temp at idle(7-800rpm). It always creeps up, haven't let it go too high because the creep is slow and it would take forever(good thing). If at a stand still I bump the gas pedal to 1500 rpm it cools right back down in less than a minute at that engine speed. After extended 3000rpm driving today(98º) I pulled over immediately and the engine was at 190º. I sat at idle for a solid 10 minutes and it crept up to 210. At this point I put it in granny gear and drove 5mph at 1500rpm, in a minute it was down to 190º and stayed there without issue. As for as I'm concerned this is simply an issue of lack of air movement through the radiator at idle. If my truck creeps 30º or more on a 98º day and it doesn't even have AC, how did these trucks with this engine and factory AC keep cool? Did GM just not expect anyone to sit at idle for extended periods? I see guys in work trucks sitting at idle with AC blasting for half an hour today, I can't imagine people didn't do this 50 years ago. I can't imagine GM simply "overlooked" sitting at idle with AC on like nobody does that. Did these trucks slowly overheat from the factory?