318 overheating

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Conch27

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A little background, I just built my first mopar, 1969 Plymouth Valiant with a decently built 318. I am pretty much new to the hot rod and muscle car world so forgive my diagnosis. My 318 is overheating, I know the timing is set correctly. I have an aluminum radiator that I got new. It has a 13 on the cap. I am running a 50/50 pre mix. What seems to be happening is that I am getting a ton of heat out of the top hose to the point it looks like it is going to pop. This is at idle after about five minutes. I took out the therm and made sure it was moving fluid and it seems to be. but after a short period it would do it again. I have a catch can. It seems like I am getting air locked once it warms up. But how.... I have yet to tune the carb fully. Thanks for any suggestions. Once I get this question please keep an eye out for Holly carb tuning, big hickup when on the gas after idle. Thanks
 
Welcome to FABO! :thumleft:

Thru this process, your going to have to answer a lot of questions regarding the cooling system, timing (not enough initial) and carb calibration (lean?).

I could write a paragraph here, but just to start with the basics.....

What are you using for a gauge and how hot is it getting?
Are you using a fan shroud?
If it's a mechanical fan, how close is it to the radiator?
Are you using a fan clutch?

You see where i'm going...:smile: More questions.

Any info you can give about the total combo will be helpful. I hope it's a simple fix.
 
I am with the old man on this one, what is your inital timing at?
As for the carb adjust the pump shot, holley has a on-line video on it.
Rick helped me alot while trying to figure out my 600 holley even though I ditched it for a 750 I had.
 
OK sorry for the lack of info. Electric fan, mounted to the radiator. 3000 rpm I believe. No shroud. I have a sunpro. I usually shut it down before it gets to hot but right to the 280 max.
 
Conch27 said:
OK sorry for the lack of info. Electric fan, mounted to the radiator. 3000 rpm I believe. No shroud. I have a sunpro. I usually shut it down before it gets to hot but right to the 280 max.
Click to expand...

Yikes!!!

Did you put the stat in a pan of boiling water and physically watch it open? Sure sounds like a thermostat issue to me at this point.
 
If it's putting big pressure and heat on the upper hose, I'm gonna say blown head gasket.
 
RustyRatRod said:
If it's putting big pressure and heat on the upper hose, I'm gonna say blown head gasket.
Click to expand...

Getting close to 280* is pretty scary.......

What happens with the radiator cap off? If it gets to 210/220, do you see obvious signs of circulation? If you happen to see a lot of bubbles in the flow, I may have to side with Rusty.
 
Yes I get circulation. I do not notice bubbles but will take another check in the am. Is it possible that I get circulation with the cap off but once it is on I get an issue? I noticed the other day I thought I had it licked and it stayed a 210 with the cap off.Next day I drove it and it over heated. Its almost like it is becoming air locked with use.?
 
I have to say, i've never personally had a air lock problem on one of these engines. Not saying it can't happen though.

With the temps and pressure you're developing, i'm trying to stay away from tuning issues at this point, so i'll ask what may be a off the wall question.......What type of belt drive are you running? Is it a stock system or one of the fancy serpentine drives? Also what water pump are you using?
 
I have a napa aluminum pump with a mach pully. Just a single belt moving the pump and alternator.
 
I like to stick to the basics first, so I have another simple question......

When you drove the car, did it run decent other then the off idle stumble?
 
yes starts and runs very well. It stays cooler longer while running but eventually rises even while cruising. As soon as I hit a light or stop she climes up.
 
Ideally you'd want an MP thermal clutch fan with the fan blades 1/2 way into the shroud. What temp will it maintain at highway speed. I'm assuming the timing/mixture are in the ballpark with no vacuum leaks & God forbid no combustion leaks & that the stat is opening all the way. Heating up at idle and or lower speeds points to inadequate water and especially air flow but with it heating up that fast that is worrysome as it might be something more serious as in combustion leaks (head gasket/cracks). You did toss the stat just for a test right & no improvement? I'd try it a highway speeds without the stat unless you're sure the stat is opening all the way & it likely is but simple things first. Keep us posted
 
OK new question on this. What direction should the flow of coolant be coming from. If I take the top hose off I am getting it pushed out the top hole of the radiator. Should it not be going to the pump from the bottom of the radiator?
 
I see one or two things happening here. 1. the water passages in the block are partially plugged or your bottom hose may be partially collapsed and 2. you have a bad water pump. If your top hose is extremely HOT like you said it leads me to believe that your water pump is not operating at 100% just enough to create bubbles but not enough for turbulant flow. These two place are where I would start 1st. 180-200 degrees is pretty normal for mopars but 280? YIKES !!!!!
 
This is an imortant question that no one asked yet.

Does it ever push water out the overflow?
If not, then it's not a head gasket.
 
might seem like a dumb question but... what temp does the electric fan come on or is it running at all?? i havent seen mention of this yet... and what temp thermostat do you have if its a 160 take it out and put a 180 in it ive had problems with the 160's staying open and temps creeping up in traffic. just doing some thinking....
 
RustyRatRod said:
If it's putting big pressure and heat on the upper hose, I'm gonna say blown head gasket.
Click to expand...
X2!
When it cools down remove the radiator cap & smell the radiator fill for combustion gases(similar to exhaust). Or run it after you filled it & bled the system of air, & see if it's got lots of bubbling going on in th cooling system with it running.
 
Okay.....my turn. lol If you've got a true 280 degree coolant, I'm thinking it's GOT to be sending quite a bit to the recovery tank, right?......if not outright overflowing it!

It DOES sound like it could be a head gasket, BUT.....the air pocket/pressure would quickly overwhelm that 13 psi radiator cap and just keep pumping coolant into the recovery tank. That's why I don't think it is a head gasket.

You should have a HEALTHY flow of coolant coming out from the top hose and flowing visibly (with the cap off) and be able to feel a ton of burning hot air being drawn across and out the back of that radiator.....almost burning off your hand! Lots of coolant flow and TONS of hot air flow. If you have a lot of air flow, but it doesn't feel very hot, you may have a defective or restrictive thermostat.

BTW, I've never even SEEN 280! If that gauge is accurate, that's wild!
 
cudavert said:
Okay.....my turn. lol If you've got a true 280 degree coolant, I'm thinking it's GOT to be sending quite a bit to the recovery tank, right?......if not outright overflowing it!

It DOES sound like it could be a head gasket, BUT.....the air pocket/pressure would quickly overwhelm that 13 psi radiator cap and just keep pumping coolant into the recovery tank. That's why I don't think it is a head gasket.
Click to expand...

That was my point in the question I asked.
No way it's a head gasket if it isn't pushing water out.
 
50/50 coolant will boil at about 265 degrees at one atm of pressure. with the cap off, it should be boiling over at around 240 degrees. Are you sure its getting that hot? Do you have access to a candy or fry thermometer you can stick into the top of the rad?
 
Conch27 said:
OK new question on this. What direction should the flow of coolant be coming from. If I take the top hose off I am getting it pushed out the top hole of the radiator. Should it not be going to the pump from the bottom of the radiator?
Click to expand...

This could be your problem right here. Coolant should be pushed from the thermostat housing to the upper hose and into the inlet on TOP of the radiator.

Coolant then returns to the motor through the bottom hose.

Sounds like you have a reverse rotation water pump from a serpentine belt drive setup. Get the correct water pump and you should be cured.
 
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