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Old 07-21-2013, 07:38 AM
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engine overheat due to intake manifold ?

I just rebuilt the 454 in my Big10 and although it runs strong the idle is rough and it runs hot. 230-240 with a 160 thermostat.

A friend (master mechanic) said the carb was too small (rochester quadrajet) leaning out causes the heat. This carb was
rebuilt at the same time as the engine and I fully trust this builder. Translation.. not fully convinced it is the carb.

So here is my question...
The 454 has a mild towing cam, Rochester QJ, Edelbrock Performer 2.0.. new radiator/thermostat/hoses/flushed cooling system.
Someone stated that the performer 2.0 is good for the peanut head .. my engine has bigger oval port heads. Has anyone heard this about the 2.0 and the peanut heads ? Could the manifold be leaning out the engine ?
Interesting thing is I have fully opened up this engine and it runs strong up to 100mph. No missing/bucking/back firing.

If this doesn't pan out what carb could I use that would be bigger than a 750 Rochester QJ ? and a spread bore to boot ?

PS .. no the head gaskets are not leaking.

One last thing.. the engine runs around 200 degrees when the outside temp is in the 80s and runs around 230-240 (redline) when its above 90 degrees. Even with 190 and 160 thermostats.

Thank you
OTGDY
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Old 07-21-2013, 08:11 AM
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check the actual fuel mix ratio.also check timing and timing advance.

late timing with lean carb can cause heat issues.
I hope you hace a fan shroud and good fan.The fan is close enough to draw enough air through the rad,,,,
The Q-jet is adequate.
also,did you put anything in front of the rad,like a trans cooler? is the rad clean? Is there a condenser in front of the rad?no bugs?
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Old 07-21-2013, 08:34 AM
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Did the builder use the correct head gaskets? There are several different designs as BBC's went thru a couple of water coolant passage changes over the years. Some require coolant passage mods to use other than OEM gaskets. Some require gasket mods to work on different blocks. Read Fel-Pro instructions on some models.
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Old 07-21-2013, 09:22 AM
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Quote:
Originally Posted by otgdy View Post
A friend (master mechanic) said the carb was too small (rochester quadrajet) leaning out causes the heat.
He's not that "master"ful, apparently. Millions of 454s came from the factory with Qjets. Sounds like your "master mechanic" is simply another Qjet hater.

Lean mixture is easy to check - read the plugs.

You rebuilt the engine why? Was it overheating before? Where the new parts exact replacements for the old ones? Is the timing chain installed correctly? Is the timing correct? Etc, etc. There are a boatload of possible causes.
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Old 07-21-2013, 09:46 AM
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Were the cylinders bored any over stock? As stated before question the head gaskets are installed correctly.

Kelly
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Old 07-21-2013, 09:55 AM
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Radiator big enough? clean and clear? lower hose not collapsing? If timing mixture ok you have cooling, or air flow issue.
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Old 07-22-2013, 09:58 AM
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Are you running a flex fan? Much better is a thermostatically operated fan clutch (below) and an OEM type 5 (or more) blade fan that fits the shroud correctly.

Some causes of overheating are:
  • Low coolant level, loss of coolant, or insufficient coolant capacity
  • Buildup of deposits that cause poor conduction of heat into the cooling system
  • A thermostat that won't open
  • Poor airflow through the radiator
  • Damaged or worn fan clutch, or broken fan
  • Collapsed radiator hose
  • Loose or defective water pump impeller
  • Defective radiator cap
  • Late ignition timing
More here.

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Old 07-22-2013, 10:33 AM
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A "small" carburator does not mean it is too lean. The fuel / air mixture determines whether the carburator is lean or rich, not the size (CFM rating) of the carburator. I knew a city constable that had a 1966 Chevrolet with a 396 CI, 265 HP, L-66 engine. The L66 motor was equipped with a 2-barrel Rochester carburator with good torque for stop and go driving but of course it fell on it face above 4,000 RPM. Install a 4-barrel Q-jet and the same engine had 325 HP.
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Old 07-22-2013, 10:46 AM
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Quote:
Originally Posted by otgdy View Post
A friend (master mechanic) said the carb was too small (rochester quadrajet) leaning out causes the heat. This carb was
rebuilt at the same time as the engine and I fully trust this builder. Translation.. not fully convinced it is the carb.
The Q-jet can flow 750-800 cfm depending on the main casting, so unless the air valve stop is keeping it from fully opening or the secondary throttle blades aren't opening fully, the cfm of the carb isn't the issue here.

Now if there's some problem w/the metering rods/jetting or the power piston spring (works like a Holley power valve), or the float level's too low, etc. that could lead to overheating. But generally speaking if the air/fuel ratio's so lean that it's causing the engine to overheat, there'll be detonation severe enough to melt pistons and beat out the rod bearings, pinch rings in their lands, and et cetera. In other words- it'll be pinging like shaking marbles in a can and no way (unless you were running open headers) that you'd miss hearing it.
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Old 07-22-2013, 11:16 AM
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Retarded initial timing advance will cause an engine to overheat. Some people retard the initial advance so they can avoid detonation on cheap 87 octane pump gas and then find out the engine runs hot and suffers from preignition. In the 1960s, the factory recommended 6 degrees initial timing advance because they did not know what octane rating the car owner was going to use. All grades of gasoline in those days still contained Tetraethyl lead and you could buy 105 octane "Ethyl" gasoline at the pump.

I alwys bought 105 octane Gulf Crest ethyl at the pump. I could fill my Dad's 1958 Studebaker Silver Hawk for $4.
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Old 07-22-2013, 07:16 PM
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"I alwys bought 105 octane Gulf Crest ethyl at the pump. I could fill my Dad's 1958 Studebaker Silver Hawk for $4. "


YES, those were the days. Before gasoline was re-formulated into denatured squirrel plss.. $,29 per gallon for Super 100 gasoline. That didn't smell like kerosene/diesel..

My first real job as a kid was at a Gulf station.. Gulf Crest gas and Atlas Buchron tires.. Best of the best.. Studebaker with a nailhead Buick in it..
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Old 07-22-2013, 10:09 PM
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I realize my questions that came to mind have been covered slightly in one way or another already but I'll pose them and then you can list how your equipped and those on here can suggest from experience if its equipped well enough to cool properly ( assuming all other mechanical and tuning settings are correct )

To zero in on what fan its using, if it is a factory fan blade and thermo coupled housing is it the unit that came factory with this truck and that engine ?. Being that its only a half ton I wondered if it has the shallow blade fan and not the deep fan blades that lets say a 3/4 would be equipped with. Naturally the deep blade with the corresponding heavy duty thermo assembly would take more HP to run but it would also move more air at idle and while cruising down the road even when the thermo clutch is not locked up. This new rad that was installed, is it the maximum core thickness that is available which typically should be used with a big block.

What is in front of the rad was already covered .. condenser with bugs or bent fins etc and if you are running the air con etc etc.

Do you know what the percentage of coolant to water the mix is and if there is any chance that a mistake was made in assuming the coolant was premixed and instead 100% glycol was poured in. Straight coolant apparently doesn't absorb heat into itself as quickly nor transfer heat out of itself into the rad near as well so its just one other item to check off the *yes its good* list.
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Old 07-23-2013, 05:18 AM
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Use one gallon of pre-mixed 50-50 anti-freeze/distilled water as a coolant. Due to the drought, some places in the southwestern United States have tap water that is reclaimed sewer water because the water storage reservoirs and lakes are going dry. If you wash your car with municipal water , it will leave a white mineral film all over the finish that has to be waxed off. I would not put that water in my engine.
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Old 07-23-2013, 05:22 AM
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
Did the builder use the correct head gaskets? There are several different designs as BBC's went thru a couple of water coolant passage changes over the years. Some require coolant passage mods to use other than OEM gaskets. Some require gasket mods to work on different blocks. Read Fel-Pro instructions on some models.
Ok now you got me thinking... The engine is a 78 and came with peanut heads. When I rebuilt it I exchanged the peanut heads with big valve oval ports. Don't remember the numbers off hand but they are popular with the racing folks. (maybe not a very smart move). Know of any place I can look up those instructions ? Hope it doesn't come to that .. what a PITA it is to pull the top off these engines in the truck.

The cooling system is stock with stock clutch fan (like above) + shroud + overflow tank. 50/50 mix antifreeze/water at first , flushed it and ran with pure water. No difference. Back to 50/50.
Haven't cleaned the condenser except with a garden hose. Thinking of using carb cleaner on it. Any other suggestions ?

Interesting this morning was a little cooler out and the engine was running at 210-220 still has 160 thermostat in it. The other day it was hotter and the engine was running 20-30 degrees hotter.


OTG

Last edited by otgdy; 07-23-2013 at 05:31 AM.
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Old 07-23-2013, 04:08 PM
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The coolant solution sounds good then. What sort of temp gauge is this as I would suggest getting your hands on a infra red heat gun and when its running at this high heat, check what the top of the rad/hose/thermostat housing readings are and also the bottom rad hose. Its worth checking into before pulling heads !.

About the thermo clutch fan assembly, do you hear it kick in and howl when it gets this hot or is it not locking up ?. I find they don't set the clutch kick in point low enough even on a brand new unit and I did some toying with the bi metal spring on my 95 chev to lower the engagement temp. Mechanical fans just don't work well in hot climates and low engine speed/ground speed, thats where electric fans shine.
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