402 Big Block Air Conditioning

[toolfool]

Please give me your advice for my truck. I have a 402 Chevy big block engine in a 1972 1/2 ton truck. It has a manual transmission, 180 degree thermostat,dual electric fans, new rebuilt water pump, engine rebuilt to 8.8 to 9.0 compression, 396c.i. 350h.p. cam, Cliff Ruggles rebuilt quadrajet with adjustable part throttle, stock-block and heads, Performer intake, stock exhaust manifords and MSD 6A ignition. It has a stock replacement Murray radiator from O'Reilley's auto parts. I am running the orange coolant at 50/50 mixture because radiator is aluminum. It has a stock reconditioned air conditioner that has been upgraded to accept 134A refrigerant. The condenser is stock. With Oklahoma 100 heat the truck runs hot with the air on on the road. Around town it does ok unless setting for a long time. The timing is at 10 degrees intial, with the vacuum advance hooked to manifold vacuum for immediate advance on start up. With the advance hooked to the timed port the truck gets hotter quicker at idle and low r.p.m.. With the air off the truck doesn't run hot. I have a stock gage and it creeps up toward half way and the air conditioner looses it's efficiency and doesn't get much hotter than a little over half way on the gage. Any advice appreciated on things to try to make things better. This is my daily driver.

[kwmech]

How big is that aluminum radiator in comparison to the big block 4 core

[toolfool]

Same.

[toolfool]

This truck is black and white so the hood is black. I have a aftermarket air cleaner that is open all the way around. I have thought about a cold air system and a heat blanket to help things.

[Tom Vogel]

How old iis that radiator? It should be professionally rotted out every 3 to 4 years if its your daily driver.
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[davischevy]

Are you running a fan clutch, and is it in good condition? Is your fan shroud in good condition? Big blocks can be hard to cool, but normally at slow speeds or stopped, not at cruising speed as you described.

I'm by no means an expert, but it sounds like the coolant is moving through the radiator too fast, IE, the thermostat is stuck open.

Good luck.

[big d's red67]

Some questions, is the engine a fresh rebuild? if so it will run a little hot till it's broken in, is the heater core new or old? have you checked to make sure water is flowing? you could have an air pocket from swithing to the new radiator. Just some things to check. I hate over heating issuses.

[turp mcspray]

Is it actually boiling over? I would check the temp with a temp gun, or try an actual gauge to see where it is really running.

[hyatt]

I would change to a 195 thermostat to slow the water flow down At higher rpm the water may not be staying in the radiator long enough to cool it Not knowing how your fans are installed make sure that they are shrouded and pulling through the entire face of radiator and seal edges of condenser to the radiator with foam to make sure air flow is maxed out I would also replace the water pump with a new not rebuilt unit In a lot of cases the impeller in rebuilts have deteriated and dont do a good job I did auto ac work for 30 years and have found these things helpful over the years Also verify that it is actually hot 50-50 mix antifreeze anf a 15 pound cap is good not to boil to 242 degrees Operating temps in 215 degree area is normal in hot areas

[toolfool]

Thanks everybody! I found out today by driving 75 m.p.h. for a while and 80 for a while on a short run on the turnpike that the motor loosened up a little and is running a little cooler. It did start getting hotter on the road with the ac off as well as with it on. Just a slow warm up. At slower speeds in town it slowly cooled down and then on the return trip didn't get as hot. I will take all the great advice and apply it.

[toolfool]

It has a dual fan set up with a good seal to the radiator fins but the condenser is not totally sealed to the radiator so I can do that. It is a new rebuild with less that 500 miles on it on the road. It dyno'd in the 330 horsepower range and that is the only time the motor had on it before install.

[TBONE1964]

Originally Posted by big d's red67

Some questions, is the engine a fresh rebuild? if so it will run a little hot till it's broken in, is the heater core new or old? have you checked to make sure water is flowing? you could have an air pocket from swithing to the new radiator. Just some things to check. I hate over heating issuses.

This would have been my first question also. Fresh builds always run a little hot. Try advancing the timing 2 degrees and see if it helps. It sounds like you have the cooling system covered fairly well. Another thing mentioned was watch to make sure the coolant is not flowing to fast to cool down and use a IR tool to check the temp as a back up to the dash gauge.

[toolfool]

The radiator is new within the year as well as the heater core. I will take the radiator cap off, turn the heater on and start the truck till the thermostat opens and the coolant flows some to make sure all the air is out. I will bump the timing up to 12 from 10. Then I may need to get the 195 thermostat in. I can get a new water pump installed after that if I am still not where I need to be. I'll get that temperature double checked also. You folks have been a big help. I don't have my dad around anymore to get me out of these jams so friends on this blog are much appreciated.

[big d's red67]

Sorry your dad isn't around to help man, be we will always help all we can on here. If you need some hands on help I'd be glad to help anytime I can since I don't live to far away over here in BA.
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[1972RedNeck]

Originally Posted by TBONE1964

Try advancing the timing 2 degrees and see if it helps.

I thought advancing the timing would make it run hotter?

[toolfool]

I will contact you if needed. Lot's of things to try first. Thanks again...

[wgr2112]

Dang, sounds like you and I have the exact same truck! Black & White 1/2 Ton 72 with 402 and A/C!

How well does it cool with the 134a?

Thought about doing the conversion as everything is there, but I also thought about doing a Vintage Air unit.

[toolfool]

Let me get this engine broke in and I will be able to give you the low down on how my truck is doing. A few hundred more miles should do it. I turned the heater on, started the truck, advanced the timing to 12 degrees from 10 and let the motor warm up until the thermostat opened and topped off the antifreeze. We have went from 95 to 85 degrees here but the engine stayed near normal. I may have had some air in the system and it likes the 12 degrees. I have never heard anyone dismayed with Vintage Air so you certainly can't go wrong with them.

[TBONE1964]

Good to hear and the temps outside are not helping anything but it is July. Since it is a fresh build, things are a little tight and that will cause temps to rise until you get a few miles on it.

[RenoKeene]

Along with the above advice (by some very, very smart people) you can 'burp' the system by jacking up just the front of the truck and running it with the cap off. Air will seek the highest point. Make sure to think this through and do it safely. I use an old set of drive on ramps with a 2x on the side of the radiator cap so the air escapes at the highest point..
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[toolfool]

I took a couple more runs on the Turner Turnpike where I can drive up to 75 m.p.h.. I vary my speed. I have about 800 miles on the engine now and it isn't heating up like it did. I did get the radiator burped. Everyone has been a big help. Now I can get a few pieces of trim replaced, wash and wax and enjoy. Take care folks.