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Well, so much for removing the fan shroud! Might have helped a little tho, drove it about 20 miles, running a 65-70 mph. The temp stayed on about 200, didn't cool down quite as good when i slowed down, or at idle.This was in about 55 degreed weather, would be ok if it would do this in 100 degree weather, but i am really afraid it will not work when the outside temp reaches that high. Really had high hopes on that fixing the problem. Thinking it has to have some cylinder combustion getting in it, can't think of anything else that i can do. Any more thoughts on it?? I did check the gauge with a therometer in the radiator, and it is within a couple of degrees.
Ah, fudge.

I know all too well what you're going through.
 

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Combustion gasses getting in coolant will only add pressure to the coolant, not heat it up.

what happens when you have combustion gases pumped into the cooling system is air pockets or gas pockets either in or around the thermostat or in the water pump.... not good.. it will over heat asap... water wont circulate if it get into the water pump... I have chased this problem many times...
 

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hmmmmm ....i still think its air flow related....

i would mount the mechanical fan back on to just to see if it makes a diffrens.....
you can also use electric fan as a pusher in comination with mechanical fan and as back up on realy hot days or when stuck in stop'n go traffic....

how about re torqueing head bolts??

also think if it head gasket related you would loose a lot of coolant
and stay hot not cool down quckly...

what grind comp cam is it??

water pump high flow or standard and how old????
 

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shroud is for lower speed cooling .

start of hot from city driving , get on the Hiway and on the edge of required air flow thru the rad.
not goimg to cool down at higher mph for awhile . very long run would be needed

cheap trick . take carboard , cutout to fit from the bottom of the valance to the radiator . if thats a low pressure area , thats where the air will go instead of thry the rad.
 

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OK, so maybe this is a dumb suggestion, but I'm not a mechanic, so cut me some slack.

Similar to DanH's idea.

Cut a piece of cardboard with an opening equal to the size of the fan and place it in front of the radiator.

If the temp stays the same on the highway, the problem is blockage from the shroud.

If the temp goes up, then it's probably something else, not airflow.

OK, let me get my flackjacket.
 

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OK, so maybe this is a dumb suggestion, but I'm not a mechanic, so cut me some slack.

Similar to DanH's idea.

Cut a piece of cardboard with an opening equal to the size of the fan and place it in front of the radiator.

If the temp stays the same on the highway, the problem is blockage from the shroud.

If the temp goes up, then it's probably something else, not airflow.

OK, let me get my flackjacket.
Your idea is good . it would show dead air or back up air .

good thinking
 

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what happens when you have combustion gases pumped into the cooling system is air pockets or gas pockets either in or around the thermostat or in the water pump.... not good.. it will over heat asap... water wont circulate if it get into the water pump... I have chased this problem many times...
I am not a super smart guy, but I am far from retarded and have so much common sense it's almost illegal, so please think on this:

If the head was cracked or the gasket leaking combustion gasses into the cooling systems there would be an extreme amount of pressure built up in the engine. There is NO way this will NOT occur, unless it is a loss of coolant issue and NOT an overheating issue.
I worked as a mechanic at a radiator shop for 3 years and dealt with heating and cooling issues every day.
The first heating issue test I did was a combustion gasses in the coolant test with a fancy schmancy chemical that turned green in the presence of Carbon.
Then I performed a pressure test, I put a cap on the radiator with a pressure gauge on it and started a cold vehicle. A crack in the head will leak combustion gasses after the first 40 to 60 seconds of running no matter how small if there's a crack.
99.9% of the time it will show as pressure building, when essentially in a coolant system in our engines the pressure does not begin to even be noticeable for 2 minutes or more. And 95% of the time it will blow past the 13 psi cap pressure within the first 5 minutes when technically the radiator is still cool to the touch.


I do not see this as his problem.... But it still does not bar it from being his problem, so you may still be right, it just don't make sense to me that it's an internal crack...
 

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Discussion Starter #54
OK, so maybe this is a dumb suggestion, but I'm not a mechanic, so cut me some slack.

Similar to DanH's idea.

Cut a piece of cardboard with an opening equal to the size of the fan and place it in front of the radiator.

If the temp stays the same on the highway, the problem is blockage from the shroud.

If the temp goes up, then it's probably something else, not airflow.

OK, let me get my flackjacket.
Got the shroud off right now, didn't seem to make much difference, took a little longer to cool down at slow speeds and idle. I am really thinking water flo, with the air cold as it is now, shouldn't even need a fan at highway speeds
 

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Discussion Starter #56 (Edited)
hmmmmm ....i still think its air flow related....

i would mount the mechanical fan back on to just to see if it makes a diffrens.....
you can also use electric fan as a pusher in comination with mechanical fan and as back up on realy hot days or when stuck in stop'n go traffic....

how about re torqueing head bolts??

also think if it head gasket related you would loose a lot of coolant
and stay hot not cool down quckly...

what grind comp cam is it??

water pump high flow or standard and how old????
Don't know about water pump, it is new tho, not rebuilt. Not sure about cam, will see if i can find spec sheet on it.
Cam is a Comp Cams 268H, has 268 duration lift and .494 lift
 

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Got the shroud off right now, didn't seem to make much difference, took a little longer to cool down at slow speeds and idle. I am really thinking water flo, with the air cold as it is now, shouldn't even need a fan at highway speeds
you useing underdriven pulley set and had a know good pump .? the the pulleys could be a flow problem . other is radiator flow per gallons of coolant/ type of fins . straight or tight pack fins can inhibit heat exchange .. three major overheating problem come from ... incomplete filled system , to small of a radiator , air flow . .. very rare is it coolant speed
 

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. very rarely is it coolant speed
I must agree.
The speed of the coolant is technically only relevant in the heater core where the volume is so small that it cools too rapidly to keep the cabin air warm.

The thermostat opens and the coolant flows rather slowly out into the radiator top tank, then as it cools the cycling of the water pump slowly pulls it down through the radiator and up into the block.

You can track this in a cool engine by hand as it warms up. The transfer of heat is rather slow as it progresses.
 

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Discussion Starter #59
you useing underdriven pulley set and had a know good pump .? the the pulleys could be a flow problem . other is radiator flow per gallons of coolant/ type of fins . straight or tight pack fins can inhibit heat exchange .. three major overheating problem come from ... incomplete filled system , to small of a radiator , air flow . .. very rare is it coolant speed
Hate to buy another new radiator, but thinking it must be the problem. The one i have now ia a three core, about the same size as the orginal radiator. Was assured that it would cool the 390. I am about ready to put this thing in a demolition derby, lol.
 

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Don't forget some of the more obvious things to check. The cooling system by itself may be totally ok.

If the total timing is off it can cause this. Too low timing will hold heat in the engine instead of getting it out the exhaust. Might be good to make sure your vaccuum advance is in good condition with that.

Carb going lean can cause this. It could just be jets but it could also be the vacuum rating on when the power valve opens. If it opens late it sets up a lean condition in the engine at certain rpm's before engine vacuum drops below the power valve opening point. You can temporarily run a vacuum gauge to the carb and tape it on the outside of your windshield to check as you are driving the car. Use good tape, LOL. That is how I do it.

A vacuum leak could also cause it because you will always tend to go leaner as you wind the engine up. A small leak can push it over into the ragged edge of red category at higher rpms.

Just other things to check for free before buying a new radiator.
 
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