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Old 05-27-2012, 06:34 PM
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350+671 blower + overheating

I have a 1957 chevy P/U with a 350 / 671 blower.I ran the truck without a hood with no problem - temps no higher than 190.After I put the hood on, temps over 210 , and spewing coolant out the overflow.If I am moving, temps will stabilize,but, as soon as I stop and idle the temps skyrocket.This leads me to think I have a fan issue.The fan is an electric pusher-not sure the cfm,but i can feel air flow through the rad.I will probably change the thermostat,and go to higher pressure rad cap...but not sure what else to do...any help would be appreciated..thanks


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Old 05-27-2012, 11:27 PM
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Pusher fans block air flow at speed. If possible a puller is the way to go. Might need to install a shroud with additional vents that open at freeway speeds. Where are you pulling you temp info from, heads or intake? Makes a difference of about 10-20 degrees.

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Old 05-28-2012, 05:40 AM
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Lack of radiator core cooling area. Lack of air flow thru the rad. (Fan cfm, ducting) The air must go thru the rad, not around it.
Air always takes the easy path flowing from high pressure to low pressure.

lack of idle timing. Blower motors typically need a lot lot of timing at idle but not so much when @WOT under boost. The out of the box distributor curve will not work. The distributor needs a specific non stock blower friendly timing curve. Especially with a big racy cam. A lack of timing at idle makes for a hot engine, hot headers and exhaust system and hot under hood temps made more critical by lack of air flow out of the engine bay.
this in turn heats up the blower case making things all the worse still.
the hot blower case and incorrect spark timing curve make the engine much more likely to detonate and knock. Hot inlet air is bad.
DO not run WOT when the blower case is hot.
Cool inlet air and a relatively cool blower case is your friend.

99% if the aftermarket electric fans don't have near enough air flow capability to keep a V8 cool. Let alone a supercharged V8 The ones that actually do, are not cheap.
You want something like 4000++cfm.

Apparently the dual fans used on the Ford Taurus SHO have fairly big combined air flow cfm. Lots of people junk yard hunt for these fans.

You want a big big efficient radiator 3 or 4 core that is not corroded or plugged up.
You want as much fan air flow as possible . More fan is better, and is never cheap.
Water pump speed is important. The pump turbine in the water pump needs to be checked. The heater hose bypass must be hooked up heater or not. The thermostat will not function correctly without at least a dummy hose connecting the water pump by pass with the intake manifold.
The best spot on the intake manifold for this is the rear water ports by the distributor on some manifolds.
Check the bottom rad hose Some go soft and collapse when hot and restrict water flow. Some require a wire coil in the lower rad hose to avoid collapse.

Overheated engine is really hard on the head gaskets. If the head gaskets are now leaking from previous overheating, the engine will overheat more easily.
Expensive engine damage will result if not corrected.
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Old 05-28-2012, 10:48 AM
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For Starters,make up a fiberglass AIR DAM,for under the front of car..like the Air Dams that Chevy put on the Camaros,when my electric fan took a dump,i was 120 miles from home,midnite,kept driving,never overheated,that air dam saved my butt.....
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Old 05-28-2012, 11:53 AM
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Loose the pusher fan. Your issue is typical of not enough fan. When you are going down the road the fan doesnt matter as natural air flow takes over. It would appear your radiator is large enough because it works fine going down the road when there is ample air flow.
Putting the hood on probably added some resistance to the pusher fans ability to push air through the radiator. A puller fan or a stock type 6 blade with a shroud would be your best bet.
Artificial Intelligence is no match for Natural Stupidity

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Old 05-28-2012, 08:13 PM
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Thanks Chet,but I can't put a puller fan on because of the blower.
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Old 05-28-2012, 08:41 PM
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use the ford fan.

how much ignition timing?
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