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Old 10-15-2012, 08:28 PM
oldbogie oldbogie is offline
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Quote:
Originally Posted by movinon View Post
Hello to all!! need some help,looking at an Elcamino 350 crate motor not sure of hp has 650 carb 373 posi.When air is on engine overheats,new alum. radiator 2 12 inch electric fans he told me it needs a 3rd 12 inch fan? the 2 now run constantly[no thermostat] keep air off he said it doesnt overheat.Do you think it just needs that 3rd fan?...thanks for the help...Don
ps 4speed stick tranny
How large is the radiator's core and are the tanks plastic or aluminum? Following that how many rows of tubes are in the radiator 1 or 2 or more and how large are they 1 inch wide or 1.25 inch wide or something else?

The problem you describe is typical of insufficient heat transfer area for the temperature gradient of the entering air. You can put as many fans on it as a DC7 has propellers and the thing will be more likely to fly than cool the engine.

Obviously when the cabin is being cooled there are two problems that result in the engine overheat:
1) Air conditioning pulls a lot of power off the engine, more power always equals more heat so the radiaitor needs to work harder.
2)The condenser being in front of the radiator is surrendering heat to the incoming air flow as well as restricting in an aerodynamic sense how much air gets to the radiator.

So the Delta T (temperature differencce) across the radiator is suffering from the flow restriction from the condenser, while it also increases the incoming air temperature to the radiator so less heat transfer can happen while more heat is being put into the coolant. Frankly I'm with your friend in calling the quits at 210, that's just to damn edgy, the down side is the engine needs to be cooled and shutting it off only lets it heat soak to a higher coolant temp. This risks cracking castings because it will get localized boiling without the movement and pump pressure present when the engine is running, sitting still engine off you're 100% dependant that the pressure cap may provide enough system wide pressure to prevent that from happening.

Somewhere in here were the words under-drive pulleys, this is a gamble for a few horsepower on the top end where the thing probably spends little time. These things are dangerous devices in the hands of people who don't appriciate what they are for. In a high RPM engine there is a point where the typical water pump develops much more flow than the engine requires, this is typically a race engine that isn't running air conditioning and is mounted in a relativily open engine room with a lot of airflow around the engine. This is nothing like the typical street driven car with all the gadgets and space restrictions one can put into the engine room. The power extraction from the water pump is an inverse parabolic curve, in that it comes up a little bit but sags against RPMs using damn little power till the RPMs start climbing above 3500 then it gets to a moderate 5 to 7 horses which grows to 20 or 30 horses at 6000. Slowing the pump if it's a production pump starves the engine for coolant flow at low to moderate speeds while reducing the high end impact. A high volume pump can restore the flow while turning slower but this begs the question how much volume is the high volume pump delivering compared to the stock pump? Unless you doing the measuring you'll find this isn't easy data to find other than a percentage aginst some unknown OEM number. So on the street just buy an OEM pump and run it with OEM pulleys and forget the games advertisers suck you into. Racers have turned them faster or slower, shaved off impellor fins and all sorts of bass-akwards tricks to walk the line between enough cooling and reducing power extration when what is needed is a variable speed or variable output pump that sees some slowing or flow reduction from variable vanes as the RPMs go up. But the complexity of such a drive or vane control causes people to shy away. The reason for the need is that pump output goes up geometrically with RPM but the engine's cooling needs go up more linearly. So the pump could use a form of regulation to put it's output into agreement with the engine's coolant flow needs besides spinning the pump and regulating the output through the enigne with a thermostat or restrictor as that doesn't address the power extraction problem of the pump.

If you're really jammed for space and can't get a larger radiator in there or some space between the condenser and radiator, maybe with scoop between them to pull up some air that hasn't been through the condenser will help. After returning to the good sense GM engineers had on pulley ratios, you may find an oil cooler mounted somewhere besides in front or behind the radiator will be helpful. Getting 50 degrees off the oil temp will typically take about 15off the coolant.

Bogie
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