# Overheating



## mshidner (Apr 11, 2009)

I have a 67 400 that has been bored .60 over. It runs hot most all the time. I have tried running different fluids, put a clutch fan on, new water pump, alum radiator, huge fan shroud, all to no avail. It still runs hot, to the point it will boil the gas out of the carb after sitting for more than a few minutes after driving it for more than 15 minutes. Has anyone ever put external mounted electric fans on? If so is it best to use a single or dual fan set up? Should one use a push or pull fan and can you a front mount fan/fans and still keep the clutch fan in place? thanks


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## geeteeohguy (Feb 2, 2008)

An electric fan is a band-aid.....you need to address the actual problem. There are several threads here on this topic....water pump spacer plate clearance is critical. Check 'em out! Good luck with it.


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## Eric Animal (Oct 28, 2007)

:agree...start with the thermostat...check the flow...


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## chuckha62 (Apr 5, 2010)

In addition to the known issues, such as a high flow t-stat and a properly clearanced water pump, make sure you have the thermal shield installed under the carburetor, most people throw this away because they don't understand what it's for. You can also block off the exhaust crossover (under the carb).


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## jmt455 (Mar 26, 2012)

Timing is critical, too. If you are using a points or HEI distributor, make sure your mechanical advance AND vacuum advance mechanisms are working properly.

I had a 455 that would never run anywhere near the thermostat setting, even after verifying the plate/impeller clearance, flushing radiator, high-flow thermostat, water wetter and on and on and on....

Turned out the mechanical advance plate was binding up and sometimes it would stick in an advanced position. When I set the timing, the plate was already partly advanced, so I was never getting the proper advance as the revs increased. Thing ran REALLY hot until I found that problem...


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## 67 GTO (Nov 26, 2011)

mshidner how did you know it was boiling the gas out of the carb? cause i have a similar problem with my 400. When it reaches 190 it starts stalling and will stall at every light and when idling? I know its either gas or vacuum


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## mshidner (Apr 11, 2009)

Hello, I took the mechanic out with me on a test drive. When the car stalled we had to let the engine crank over and over until we could get gas back into the carb. Once we got the gas into the bowls again the car ran fine. I currently have a Holley on the car but I am going back to a Quadra jet for the looks. I am running a Edelbrock Pontiac Performer with a heat shield. The mechanic took a temp gun with us and measured the heat coming off the water jacket where the 160 thermostat is and it was reading over 230 after we turned the engine off. We have checked the thermostat and timing and they are both right on. I had the HEI distributor pulled and it checked out ok. The odd thing is where I live in the rockies once the outside temp drops below 65 the car will run at about 200 to 210 all day long unless I do a lot of stop and go. I have had the radiator checked out and it is like brand new. So I am at a loss so far on what to do. So my question is I am down to the clutch fan and and maybe the brand new water pump being bad. Even with the old water pump I had the same problem with it as I do with the new pump so I do not think it is the water pump. My question is why do some people use electric fans and it takes care of the problem when they have tried everything else?


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## jmt455 (Mar 26, 2012)

I've not had much luck with the electric fan solution. Every time I've had cooling issues, it turned out to be something (or combination of things) within the cooling, fuel and/or ignition systems that created the problem. You don't want to add a pusher fan with the mechanical fan left in place; that usually causes more trouble with air flow through the radiator. You could try replacing the mechanical fan with a good (electric) puller fan and shroud, but you really should be able to count on the cooling system working properly with the mechanical fan if this is a "street" engine.

Having the coolant temperature climb to 230F after shutting the engine off is not necessarily a problem. The coolant temperature in the engine WILL increase after shut-down as the latent heat is absorbed by the coolant. 

Operating temperatures of 200-210F are not overheating, but it does seem that your operating temperatures should be closer to your thermostat setting and the fuel vaporization problem has to be addressed.

Is the engine consuming coolant? You might have a combustion chamber leak that is heating the coolant. Any evidence of coolant on plugs? Any bubbles in the coolant when you start the engine and watch the coolant in the radiator? That would indicate combustion gases being forced into the cooling system through a bad head gasket, cracked cylinder or head, etc.

Is the carb set up properly? Lean mixtures will generate additional heat.

Pontiac V8s were originally equipped with 195F thermostats. A 180F thermostat usually provides the best balance between quick warm-ups and efficient operating temperatures.

At the operating temperatures you mention, there should be about a 40F temperature drop from the radiator inlet to the radiator outlet. For example, if coolant coming into the radiator from the water outlet/thermostat is 210F, it should be returning to the water pump at about 160-170F. If the temperature gradient is less than that, you either have a flow restriction in the radiator, poor coolant flow from the pump, or poor airflow through the radiator. If the timing is correct and you have an aluminum rad with proper clearance between the divider plate and the impeller, you should see strong flow and a big drop in temperature as the coolant moves through the radiator.

Are you getting adequate flow through the radiator? With the radiator cap off, start the engine and watch the coolant as the engine warms up. You should be able to see evidence of significant coolant flow as the thermostat opens. If not, there is something impeding coolant flow through the water pump, the thermostat, the heater core, the radiator hoses or the radiator.

Are you using a heavy duty fan clutch with an appropriate diameter (I like the 19.5") fan?

Does the fan clutch work properly? At those operating temperatures (approaching 230F), the clutch should be engaging and you should definitely hear the difference when the fan speed increases. The Hayden 2797 is a good choice.

Are you using the proper fan? I've seen people use the wrong pitch and even the wrong rotation fans...

Is the fan blade properly positioned in the shroud? (about 2/3 of the blade inside the shroud and 1/3 of the blade should be rearward of the shroud)

Do the shroud opening and fan diameter match? The fan blades should almost fill the opening in the shroud. There should be about 1" of open space between the edge of the blades and the inside edge of the shroud opening. 

Does the shroud fit snugly to the radiator/core support? There should not be room for airflow to get pulled into the fan without going through the radiator.

Maybe you've been through all of this, but in my experience there is usually a combination of factors that contribute to the high operating temperatures and everything has to be right.


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## chuckha62 (Apr 5, 2010)

You mention a new water pump and an old water pump... Did you (or your mechanic) properly clearance the cavitation plate behind the water pump? When I pulled mine off recently, it was well over 1/4" away from the impellers. As I understand it, you want the plate to be within 1/10" from the impellers in order for the water pump to flow properly. 

Also, as I understand it, those temperature guns read most accurately when pointed at a black surface, not a painted light metallic blue, chrome, or other color thermostat housing. Your reading at the T-stat housing may not have been all that accurate.


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## geeteeohguy (Feb 2, 2008)

I mentioned the pump clearance issue on my first reply to this post back on the 16th....and I'll say it again, that's the first place to start.


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> I mentioned the pump clearance issue on my first reply to this post back on the 16th....and I'll say it again, that's the first place to start.


:agree Listen to the man... :agree If that plate clearance isn't right, you can't SPEND enough money on it to make it cool.

Bear


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## jmt455 (Mar 26, 2012)

BearGFR said:


> :agree Listen to the man... :agree If that plate clearance isn't right, you can't SPEND enough money on it to make it cool.
> 
> Bear


^X2! 

These guys are right; everything else I mentioned in my previous posts should come AFTER you verify the pump is doing what it's supposed to do!


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## mshidner (Apr 11, 2009)

We took the pump off again yesterday and it is about 1/8 to 1/16 inch clearance. The carb is jetted on the rich side and we get a little bit of black soot at the tailpipe. My overflow tank never lets any anti freeze out. It stays where it supposed to be. We looked at the movement of water thru the top of the radiator and it moves very well with no air bubbles. Also nothing in the oil. Good compression in all cylinders. But I still get too much heat in the engine compartment resulting in a loss of gas in the Holley carb bowls. Maybe I am not actually overheating but for some reason I am getting too much heat in the engine compartment resulting in the boiling of the gas. I do have a hood pad that was on the car when I got it. The previous owner complained of the same issue that I am having. Even on the hottest days the temp gauge which has been replaced and bench tested will get up to about the 90% mark. It has never completely pegged the gauge but the engine compartment is extremely hot.


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## mshidner (Apr 11, 2009)

A couple of other things we did yesterday. The seven blade fan is about 2/3 in the shroud. The shroud is attached tight to the radiator but we added some weather stripping about 1/4 inch thick yesterday between the shroud and the radiatior. I am going to get a new clutch to see if this one is bad. What if I got a solid attachment instead of the clutch? Thanks


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## geeteeohguy (Feb 2, 2008)

A clutch is best. The Hayden unit mentioned before is a good choice.


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## Rukee (Feb 8, 2007)

Have you ever shot the motor with a laser temp gun so you know the exact temps its running??Shoot the bottom of the thermostat housing and see what you get, you can probably borrow one from a parts store.

And are you running ethanol free gas?


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## BearGFR (Aug 25, 2008)

mshidner said:


> We took the pump off again yesterday and it is about 1/8 to 1/16 inch clearance...


There's your problem. That's too much. Clearance should be no more than the thickness of the compressed gasket. In fact, that's the best way to set it: put the plate on the back of the pump with no gasket, "work" the plate until barely touches the impeller all the way around. When you put the gasket back in place, clearance will be right where it needs to be.

Bear


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## chuckha62 (Apr 5, 2010)

For the fuel "boiling" issue: If necessary (and this is what I did) and you're running the stock intake, remove the carb and you should see two holes in the channel in front of the primary inlets. These holes are (I believe) 11/32" and can be plugged to limit the amount of thermal transfer from the exhaust crossover. This was a one year design that was abandoned after '67. Plug these in addition to using the stainless steel plate and you'll cut the heat way down under the float bowl.

Just a thought...

Chuck


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## mshidner (Apr 11, 2009)

I am running a Edelbrock Pontiac Preformer intake and a Holley carb. I will switching over to a Quadra jet in about a month. But I will still be using the Edelbrock. Thanks


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