Temperature hunting at stop lights

Rustisbest said:

Was the original a copper/brass radiator? From what I understand the aluminum radiators have a higher fin count so the thicker they are the more restrictive they become. Supposedly the 2 row aluminum is equivalent to the old 4 row copper/brass. My own junk just has the parts store plastic tank ones that come on just about everything on the road nowadays

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Yes. It was a copper/brass radiator. Aluminum does carry heat away very well. I have read about the airflow of aluminum before. But I was concerned about moving my shroud with the thinner radiator. Plus I do use the truck to haul about 8k lbs from time to time. I wanted the extra cooling capacity. I'll try the severe duty fan clutch. When that doesnt work, I may raise the thermostat to a 195 degree so the swing is less noticeable I may also get a more aggressive fan if I can find the right thing. I am a bit disillusioned regarding GM after factory parts. I thought they would be better than they are.

I’ll list the parts that have worked for my ‘75 K25. YMMV

- Original SBC steel fan and shroud, which was part of the factory HD cooling package
- severe duty fan clutch
- Stewart high flow water pump and 195 degree high flow Robert Shaw thermostat
- Champion aluminum 3 row (I think) radiator from Jegs. It was the CU161 equivalent.

Last weekend it was about 85 degrees here and I had the truck idling while I added some R134a and cleaned up odds and ends in the engine compartment. It idled with A/C on for about 40 minutes, and the temp on my mechanical aftermarket gauge stabilized at about 197 (maybe the 195 degree thermostat is a little lazy). Highway temp reading is similar.

Mine doesn't go over 180 but it floats between 170-180 with a 160 T stat but it's also a 388 with 11.5:1. 170 driving around 25-65mph but at a stop light or sitting in the lot idling it jumps to 180 and stays there but as soon as I start moving and get that air pushing into that brick of a front end it drops in seconds back down to 170. This is with a 2 row aluminum rad a 3 blade mechanical race fan and half a "shroud".

gmbellew said:

Does the shroud sit up nice and tight to the radiator? The shroud needs to be up against the radiator for the fan to pull the air through.

Is 180 the right thermostat? My 1990 350tbi runs a 195. Maybe 454 is different?

Also, the gauge isn’t always super accurate….you might be just fine at just under 210 on the gauge at a long idle. Actual temp might be a lot less.

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I found 1” gaps between the shroud and the radiator on both sides. Top and bottom fit good. Attached is a picture of the driver side. I also attached a picture of the old radiator. There is nothing specific about the tanks that would fill that gap.

Copper is a more efficient conductor of heat than aluminum. All aluminum radiators are not constructed the same. A good Aluminum radiator is equal to a good brass,copper radiator. A budget aluminum radiator is possibly not as good as the factory radiator. I forget all the specifics. I think it was something to do with the size, thickness and construction of the aluminum tubes. Do research more than just price checking if switching to aluminum.
Make sure it really is a benefit for your truck.

Ricko1966 said:

Copper is a more efficient conductor of heat than aluminum. All aluminum radiators are not constructed the same. A good Aluminum radiator is equal to a good brass copper radiator. A budget aluminum radiator is possibly not as good as the factory radiator. I forget all the specifics. I think it was something to do with the size thickness and construction of the aluminum tubed. Do research more than just price checking if switching to aluminum
Make sure it really is a benefit for your truck.

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The core construction and layout will definitely make a difference 2 wide cores vs 4 narrow cores in the same overall space. Air and water flow/turbulence will make these work entirely different.

I've found if their 2 core is the same thickness as their 3 and 4 core rads the lesser cores might actually work better due to air and water flow. Metal tanks also dissipate heat plastic does not. I've also had bad luck with the plastic tanks blowing seals or cracking.

SOLVED: Welp after all that, I took the truck up to my friend’s garage this morning and we checked the timing. It was off by about several degrees. We thought maybe the balancer was spun. But nope, just needed to be adjusted. I think someone along the way adjusted it improperly. Runs great now and the problem with heating up at stop lights is pretty much resolved.

I took the truck 5 miles down the road to get it up to temperature. I stopped on an empty stretch of the road in direct Florida afternoon sun and heat with no breeze. I waited for 3 full minutes to simulate a long traffic light. The temperature gauge didnt budge. 100% fixed. AI says the reason for the temperature rising at stop lights is due to combustion continuing through to the exhaust stroke. Extra hot gasses transferring to the exhaust manifolds and less airflow at stop lights. The engine was not running at peak efficiency. Moving on to the next thing: transmission leak

I've just recently found out a major difference between brass and aluminum radiators. Brass tubes are more efficient than aluminum. That's why new aluminum has a wider tube design. 2 core wide tube aluminum = 4 core brass. Longer fin contact transfers more heat. Switched my 73 454 to aluminum 4 core and would boil over in traffic even with electric helper fans. Waiting on new 3 core wide to come in. Dfw traffic sucks.

electoqute said:

I've just recently found out a major difference between brass and aluminum radiators. Brass tubes are more efficient than aluminum. That's why new aluminum has a wider tube design. 2 core wide tube aluminum = 4 core brass. Longer fin contact transfers more heat. Switched my 73 454 to aluminum 4 core and would boil over in traffic even with electric helper fans. Waiting on new 3 core wide to come in. Dfw traffic sucks.

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Let us know how the 3-core does. My issue was definitely engine timing. Now my temp goes up a little until the thermostat opens then steady’s off