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Hey guys, I'm a newbie to this site. Have I got a problem or WHAT?

I have been chasin a heating problem since April of 2019 on a project truck. Didn't realize it would be this hard. Bought a 69 GMC pickup. All stock. It had been sitting of r not sure maybe 8-10 years. I did all the replacements normal to get running to see what I had. Had to replace the TH 350. Got it running and the Engine ran hot. At idle or driving. I replaced all the hoses and belts, went from a 2 row copper to 4 row aluminum radiator with two 1730 cfm (3460 cfm) fans on a sensor. Changed water pump. Put a high out put and OEM replacement. lower hose new that I had replaced did not have a spring.....replaced the new hose. tried several different thermostats. 180-195. The engine ran good .used on water did boil over a little a few times before the new radiator but not since. It always went up to 230 even 250 once. It had a 2 barrel and stock intake. I jerked the engine out had it boiled and had it stroked to a 383. 10:5-1 pistons, Aluminum head, (Flo Tech 180CC) roller cam and roller rockers, 750 Holley vacuum secondary's. All new A/C system, new distributor, hooker headers, 3 chamber flow masters.
Everything under the hood is now new except the power steering pump. It runs all day long down the road ......100 miles with A/C on at 60,70 mph at 195-205 degrees. Get in stop and go traffic and it starts building up heat again to 230.Fan rotations are correct. I have two fans pushers on the a/c condenser and two pullers w/ full shroud and the radiator. 50/50 coolant. One heater supply line comes off the pump goes to the heater core and returns to the upper end of the radiator tank. I have been playing with the timing for two weeks off and on. I had it at 5 degrees idle (550) and 25 @ 3200. Now it is at 12 idle and 33 total. No vacuum. I left vacuum unhooked because it goes up over 65 with vacuum. Engine builder said to keep it below 40 so I cant connect unless I change weights and springs but haven't yet. That is a can I don't know if I need to open. Anyone have a magic bullet? No one I know has been able to solve this problem. I am ....?
 

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Timing!
You need lots of initial. Likely up close to 20 degrees. And then 12-14 mechanical plus a limited 10 from vac advance.
Read this.


Where in the world are you located?
 

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Always start with the simple stuff.

So lets talk about your radiator cap. What psi are you running and have you checked the psi to ensure it is not opening early or not sealing at all? A oil pressure gauge can be ran off of a T on one of your heater hoses to check for pressure.

Is your radiator cap the highest point in the system? Are there any spots where air could be trapped?

Have you put air into your spark plug holes pressurizing the cylinders around 20psi to check for head gasket leaks?

Have you run water through your heater core in both directions to make sure it is not blocked?

Are you running the factory manifold with the butterfly valve or have a cat located close to the engine?
Your headers will glow if your getting heat from these.

Have you ran the factory 7 blade clutch fan?
 

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Heater lines are wrong. The supply should come off the intake before the thermostat, this is the pressure supply side. Return should either be to thee cold side of the radiator if there is a fitting or a Tee in the pump let hose on some models or to the classic is the upper fitting of the coolant pump which is the suction side. The fitting on the top of the pump is internally cored to the impeller inlet.

You probably have an excess of fans. A thermostatically controlled 7 blade fan on the pump in a shroud is what the factory system should have been. Electric fans have a difficult time duplicating the air flow of a single factory fan.

Vacuum advance only functions when vacuum is high, it goes away as the throttle is opened. Adding to the base timing requires that that amounts over about 10 degrees need to be equally removed from the centrifugal. Excess advance usually leads to back fires, insufficient advance leads to overheating.

Bogie
 

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Discussion Starter · #6 ·

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Rod...from a Chrysler?
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Have you tried running without the pusher fans? Not turned off, but completely removed.
 

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X2 on the pusher fans.
Sometimes at idle or low speed they can pull hot air over the top of the rad from above the motor. That usually happens when the Underhood bracing/structure has been moved or removed. No seal to the rad cradle anymore.
 
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