Cooling Problem.. Help Please

[IntegratedTJ]

Got a fresh engine build here. Hey so upon further inspection, the engine is overheating at idle. As soon as I hit the pedal, the temp shoots right back down to where it should be (almost a 30-40 degree difference)

Already:

Replaced the thermostat
Bled the cooling system

Thoughts:
Original radiator from 1972..
Water pump..?
Exhaust in cooling system

Help please.

[cdowns]

get a new radiator// with a proper fitting shroud

[IntegratedTJ]

Originally Posted by cdowns

get a new radiator// with a proper fitting shroud

You sound pretty confident with that answer?

[Wrenchbender Ret]

Almost sounds like something with the gauge. If you have acces to a laser thermometer you can find out what is really happening. I can't imagine that much change in a very short time.

[alsriv2]

Originally Posted by cdowns

get a new radiator// with a proper fitting shroud

Not sure about the "new radiator" part of this as we have no idea the condition of yours, however, it is not a bad idea.
More than likely lack of good airflow due to missing or incorrect shroud will cause the problems you describe.
How is your fan? Original or after market? AC? Clutch fan or straight drive? Answers to these questions will help diagnose your overall problems.

[IntegratedTJ]

Originally Posted by alsriv2

Not sure about the "new radiator" part of this as we have no idea the condition of yours, however, it is not a bad idea.
More than likely lack of good airflow due to missing or incorrect shroud will cause the problems you describe.
How is your fan? Original or after market? AC? Clutch fan or straight drive? Answers to these questions will help diagnose your overall problems.

The engine is a car/light duty truck replacement GM Goodwrench Crate 350. It's the stock radiator from 1972. It sat out of the truck for a long time, truck overheated and warped a head, now it is back in, and I used the same cooling components. Original radiator, original fan shroud, original fan, aftermarket fan clutch, water pump on this motor doesnt look the same as the original water pump, however this one currently installed does look the same as ones I look up for a 350 waterpump. Edit: If it helps, while I was bleeding the cooling system (I used a 2 liter bottle with the bottom cut off and used electrical tape to seal it. I know it sounds bad, but it works.) the coolant would raise all the way to the top of the bottle when it would get hot, and suck down in to the radiator as soon as the gas was pressed. So, when it gets hotter, at idle, the coolant rises in the radiator, but as soon as I hit the pedal (temp goes down), the coolant goes right back down in to the radiator. It's a very immediate reaction, too. That's what lead me to also think that my radiator may be gummed up? I dont know.. I'm kinda scratchin my head.
EDIT: No AC.
EDIT 2: No heater core hooked up.

[cdowns]

Originally Posted by IntegratedTJ

You sound pretty confident with that answer?

nah just use that 40 year old radiator it's easy enough to change out your motor when you heat it up

[alsriv2]

Originally Posted by cdowns

nah just use that 40 year old radiator it's easy enough to change out your motor when you heat it up

Your description sounds like a blocked or partially blocked radiator. As the engine warms up with the radiator cap off, you should see coolant flow across the top of the inside radiator without pushing fluid up and down with RPM change.
Replace your radiator or have it cleaned professionally.
That pugged condition is probably what toasted your previous engine.

[Justin@EntropyRad]

Can help in that department!

Baller Setup: http://www.entropyrad.com/1967-1972-...-radiator.html

Driver Setup: http://www.speedcooling.com/1967-197...r/prod_38.html

[Jonlopes]

If you bored out the engine in the build it will require a little more cooling performance due to less cyl wall thickness. If your old radiator was just enough the build may have pushed it over the top.

I had a 66 gto that had a very well worn engine. it was just fine running the stock 3 row radiator but it ran very hot with the .060 overbored rebuild and I had to have it re-cored to 4 core.

Blockages/ plugged core tubes will also cause the same issues you mentioned.

[1968aj]

IF ITS BLOWING COOLANT OUT THERMOSTAT MAY BE STICKING. you can get a bad new one. I have. put thermostat on stove in a pan of water see if it opens.

[GASoline71]

Never heard of needing more cooling after an overbore...

However, even though Mr. cdowns was blunt with his answer... he makes a good point. If you're trying to cool down any engine with a worn out 40 year old radiator full of rust and crust... you'll have problems.

No way would I reuse a 40 year old untouched stock radiator with a brand new engine. Eithe you'll probably need a new radiator, or have it recored or rodded out.

Gary

[Justin@EntropyRad]

There is some weight to the overbore theory...if the walls are thinner, they can allow heat transfer or hot sport between cylinders, assuming the sleeves and/or cooling jackets are that close together

Running a crust-o-matic 40yr old rad might not help either.

Always start with the simple things first: coolant level, t-stat, air, fans, rad

[swamp rat]

Any good radiator shop can flow test a radiator to let you know if its plugged up. The fact that the coolant pulls into the radiator when reved me leads me to think its flowing ok.

You don't have the heater core hooked up, did you run a bypass hose? and are you sure its routed correctly? can you post a pic? if its on the intake and the wrong water pump port it could be a problem.

[In The Ten Ring]

Originally Posted by GASoline71

Never heard of needing more cooling after an overbore...

However, even though Mr. cdowns was blunt with his answer... he makes a good point. If you're trying to cool down any engine with a worn out 40 year old radiator full of rust and crust... you'll have problems.

No way would I reuse a 40 year old untouched stock radiator with a brand new engine. Eithe you'll probably need a new radiator, or have it recored or rodded out.

Gary

I like "cdowns" and I say this with some degree of authority because he really ticked me off with some terse answer of his. I am new to this truck rebuild game but a new radiator (with more rows) was one of the first things I bought when I started working on my truck. The PO told me that the radiator in the truck was out of a junkyard because he dropped a tool on the original radiator and knocked a hole into it. The radiator (out of junkyard) looks to be a 1-row and is very crusty outside. I assume the PO put tap water into it?

I'd try another thermostat and then look into a new radiator. I bought a 3 row at Advance Auto for around $200.00.

[70blackfish]

do you have your fan installed correctly ? don't laugh i have seen it before. left untouched the blades will fly off , and hopefully not through the hood...

[jerry moss]

if i read your post correctly it was overheating before and the only common denominator is the old radiator. when you install a new thermostat always drill a small hole on the outer edge of the t-stat to help bleed air out and allow a small amount of coolant to move even when cold.

[Coley]

Originally Posted by cdowns

nah just use that 40 year old radiator it's easy enough to change out your motor when you heat it up

atta boy CD....still knockin' it outta the park with fabulous, positive 'can do' attitude....lol

Coley

[Justin@EntropyRad]

any results from the overheating issue?