Big Block Overheat

[Al Tyson]

I just had my 427 rebuilt. I also had the radiator pressure checked. New water pump and thermostat. Hoses are fine. It overheats in 5 minutes. I removed the thermostat and same thing. I installed an aftermarket A/C unit with heat control valve but even if the valve was closed I don't see why I should overheat.

Al

[Iron Duke NCRS #22045]

Additional questions for clarification

Did you also have the radiator flow checked to see if it is internally restrictied? Can the tube condition be visually inspected from the cap opening? Did the engine overheat before the rebuild? What model year is the car and what is the production horsepower rating, and is it modified?

Duke

[Tony H.]

Other questions for clarification

Can you quantify "overheating" and compare to opertion before rebuild? Were gauge and/or temp sender changed? Have you verified temperature of the hoses? You could use a candy/baking thermometer wrapped around a hose as a crude method or use an infrared thermometer if you have access to one.

[Al Tyson]

Re: Other questions for clarification

The engine is a 427/390 hp. The engine did not overheat before the rebuild. I didn't have to check with a digital thermometer. It boiled over.

Al

[Big Block George]

Here's what ya gotta do.......

pull the radiatior, look at the cooling fins, I bet at least 40% of the fins are bent, crushed, mangled, painted shut, in other words, wherever the cooling fin is bent, no air travel through that part of radiator. Use a pair of thin screw drivers and straighten the cooling fins, on both sides. It is extremely tedious and time consuming work, but well worth it. You will increase air flow, plus the radiator will look like a radiator.

[grr]

Re: Additional to Duke's question.

Like Duke said check the flow through the radiator, feel your hoses etc. Since you removed the thermostat you seem to feel you have a flow restriction. I know this sounds stupid so don't take it that way, but did you check the radiator core to see if anyone may have stuck something into the unit during the pressure check and failed to remove it. Little hick-ups like this happen.Good luck,grr#33570

[Jerry Clark]

Wait a Second

that's my Florida name, ( not George ) BB Jerry, you're treading on dangerous ground here George...

jer

[Richard S.]

Re: Wait a Second

I'm having the exact same problem with my 66 427/390. It runs cool on the highway(180)but overheats at idle after about 20 minutes. I changed the fan clutch to a Fred Oliva rebuilt unit(a beautiful job and I would highly recommend him) with no change so it's not that. The car was restored six years ago and the rad was recored at that time. It's been running like this since. I'm now going to try installing the A/C cars foam on the shroud and water wetter to see if that will help at all.

[Robert C.]

Re: Try this for boil over

Let me suggest one change for both you guys that boil over. Get one of those STANT radiator caps with the red lever (that de=pressurizes when pulled) and 16 Lb. pressure. If you have a 40%/60%coolent mix and one of these caps, I don't think you will boil over. If the car KEEPS its' coolent contained the engine temp doesn't make difference. If you still boil over install an overflow bottle so that you don't really LOSE any coolent. I have a regular small block alum. overflow resevoir and I've installed a SECOND plastic over bottle!


Texas Chapter NCRS

[Big Block George]

Vel now Herr BB Clark from Florida....

langsam wit deine name of Big Block. I vil sent da Gestopo to yo doe an' hav dem take you avai, navah to be heard agin.

[Don O'Connell #33101]

Re: Try this for boil over

Al,

I second Bob's post. I had some A/C work done last year (427/400 '69) and had them change the heater core while they were there. Seems they "gave" me a new radiator cap in the process. The car boiled over for the next couple of days as I replaced the thermostat and checked the fan, clutch, radiator fins, etc..

Bought the same Slant 16lb cap with the red lever and my problem went away. Seems the "free" radiator cap couldn't keep the pressure in and hence lowered the boiling point.

my 2 pennies.

Don

[Al Tyson]

Re: Big Block Overheat

I have a Stant 14 lb cap. My question is how to you check a water pump? One suggestions is to take off the radiator cap when cold, start the engine and I should see the water swirling. Someone else suggested that I take a clear hose and attach to the output of the waterpump and see the flow.

I had the radiator out and had it pressure checked. I also straightened out any fins that were bent. There maybe a couple bent but that shouldn't make it boil over in 5 mintues.

Also can a radiator shop check the flow with the radiator in the car?

Al

[Tom B.]

Re: Big Block Overheat

Al,

If you make a return trip to the radiator shop, have them test for hot gasses that may be entering into your cooling system. I would hope that wouldn't be the case (it's a head gasket problem), but one of the symptoms is a rapid increase in engine temperature, usually in just a matter of minutes, like you described. You did mention that you just had your engine rebuilt. Best of luck. TBarr #24014

[motorman]

Re: Big Block Overheat

you must take the rad out to check the flow in GPM. also there are 2 different depths to the filler necks on rads so make sure that the cap you get this the one for your application.

[motorman]

Re: Big Block Overheat

have you had your system pressured checked? this is where they put a pressure pump on the filler neck and pump the system up to about 20#/30# and see if it holds for a long period of time. do this when it is cold and the pressure should stay for hours. does your bottom rad hose have the spring in it.i have seen the spring move up towards the pump and then the hose will suck shut and cause no water to flow. on race cars we pull the spring end outside the hose on the rad end and put it under the hose clamp so it can not move.