Thread: 390 problems

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Hey there i have been having some issues with the 390 i just built and installed in my 68 wagon. Its a 1966 390 600cfm edlebrock 4bbl with brand new everything and a 3 core core radiator with a 180 thermostat and duel electric fans. Hopefully someone can help me. It overheats while idling but cools to normal while ddiving. Also my heads where they meet the exhaust manifolds are turning white as if it was running super hot. Any thoughts.? I replaced the thermostat bled the system and nothing. Its driving me crazy. Dont think the head gaskets are on backwards.

Possible water pump issue, lack of flow at idle. Did you use the same pulleys or aftermarket?
Possible head gasket issue or even timing problem, cam and distributor should be verified. And don't forget to verify the timing mark at the dampener. Sometimes zero isn't zero, needs verification.

It sounds like you either have a lean condition due to a carb setting being wrong or the timing is wrong and the combustion cycle hasn't completed but it's being pushed out the head.

I have checked to see if water pump was flowing. Dont know how much it flows. But i had this running hot problem with my msd and so i switched to a stock dist with an electronic crane cam pickup. Which seems to work good. It runs great and has a good amount of power buti feel its lacking with all i have done to it. I do have an original cruise o matic in it tho. But even with this new dist same problem. I remember putting in the timing chain and cam and had set it on zero and had two other mechanics double check me. And the balancer.only went on one way.

I had a 68 460 that did that. Also had 2 fans. When I put an electric fan sending unit and switch in, to make the fans come on earlier, it fixed the problem.
My fans were in the engine side of the radiator close to the motor blowing air onto the motor.

Originally Posted by 68montego

I have checked to see if water pump was flowing. Dont know how much it flows. But i had this running hot problem with my msd and so i switched to a stock dist with an electronic crane cam pickup. Which seems to work good. It runs great and has a good amount of power buti feel its lacking with all i have done to it. I do have an original cruise o matic in it tho. But even with this new dist same problem. I remember putting in the timing chain and cam and had set it on zero and had two other mechanics double check me. And the balancer.only went on one way.

Sometimes the balancer fails where the outside turns and comes out of alignment. If you can bring # 1 cylinder to TDC using a piston stop, then see if the balancer still lines up with tdc. Could you see coolant moving in the radiator? Try the other suggestion and run the fans manually so they come on earlier. Worth a try.

Also how are you measuring this temp? Factory gauge? or aftermarket?

I will have to do that this weekend and see what it says. I have my fans on all the time. And it still overheats. Its a powerforce dampener. And i have a mechanical sun pro gauge. Worked great with my 302 that was in there before the 390. You think its a possibility that it could be the rad. Cause i never gotone for the big block. Its a 302 one. Didnt know.it.mattered that much figured it would work.

I think you just hit the nail on the head, you don't have enough radiator.

Originally Posted by 68montego

Worked great with my 302 that was in there before the 390. You think its a possibility that it could be the rad. Cause i never gotone for the big block. Its a 302 one. Didnt know.it.mattered that much figured it would work.

Yeah, it could be that the rad is just to small but, it cools at speed when there is increased airflow. Your fans have shrouds? Is the full radiator core being used by the fans? Or is it that there are areas of the radiator that aren't covered by the fans? If your not pulling air through the whole radiator with your fan(s), then that's more likely your issue.

You might be better off (if your fans don't use the whole core) to go back to the mechanical fan and use a shroud that covers the complete core with a fan with more than 4 blades that fits snug in the shroud.

I was going to use a stock fan but it wouldnt fit between my engine and rad. I have two 12 inch fans and they cover the whole rad minus the takes. They are mounted on the front of the rad amnd blow air thru the rad. They are in their own little shrouds. So im pushing air thru. Should i switch them?

It's generally accepted that pulling air into the rad is better than pushing. And what's "minus that takes"?

Originally Posted by 34_40

It's generally accepted that pulling air into the rad is better than pushing. And what's "minus that takes"?

Mike, I think he means "minus the tanks" ;-)

Yes i meant tanks. Im using my phone for all of this. Its my only computer as of right now. Sometimes i hit the wrong letters. Anyway i have about 4 or 5 inches between the very front of the motor which is the water pump pulley to the rad so i found a 4 core aluminum rad for a big block that im going to buy and get rid of the 3 core 302 one. I have been trying to upload a picture and i cant figure it out on this.

Originally Posted by randyr

Mike, I think he means "minus the tanks" ;-)

DUH!! TANKS ! Thanks Randy!

With the fans in front of the radiator the mounts and shrouds are blocking airflow! That's why it's preferred to be inside (motor side) that maybe the central problem for your setup right there! More rows to the core isn't always the answer either as the thicker core has more restriction.

I would encourage you to figure out a way to move the fans to the inside and pull the air through the core first. It may save you a lot of money?

get a Lincoln Mk* fan and put it on the back side of the radiator---if your fans don't need 45 amps they aren't big enough
fans mounted on the front of rad block airflow--

The heads on the fe engines have a lot of exhaust port that is exposed to air and doesn't have any water around the port so its not unusual for the paint to burn off there

I think each fan is 25 or under amps. So dontnecessarily need a 4 core. Im sellingmy brother my rad for his 302 so i can get a big block one so the port for the bottom rad hose will be on the right side since the outlet for the water pump is opposite as the 302. Just deciding whether to get3 or 4 core. I will switch the fans hopefully today and see what happens. Ok well that explains paint burn off. Will still have to recheck actually timing thisweekend hopeully