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Old 02-05-2003, 07:27 AM
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Post SBC - effective cooling / electric fan sensor

OK - replacing my earlier post, I have a Ron Francis electic fan switch (in 3/8" NPT buts lets ignore that) which cuts in at 176 degrees (80'C to me) and they say should be in the head. Tech' info on this site suggests that under pressure the boiling point rises to perhaps 230+ and OEM fans cut in not far before this, though perhaps around 200' is good running temp? I expect to need the fan only when stationery (not hot in the UK) so with a 176' sender I reckon I need to position the sensor where it will measure the coolant AFTER being cooled, otherwise it would be on all the time??. As I understand it on a SBC the collest part is the bottom of the radiator - so I could fit a plug into the radiator base or tap into a solid tube in bottom hose.
Does this line of argument make sense?? Does real experience suggest otherwise??
Please help! thanks Limey
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Old 02-05-2003, 07:45 AM
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The crunch is this - I have a 180 degree thermostat, so if I ran the 176 degree switch on the way into the rad (eg on the waterneck) it would always run the fan? (don't want this)

Anybody know what sort of temperature drop to expect across a (Walker) rad with a SBC? - ie if I mount the 176' switch at the bottom of the radiator (assuming this is the OUT pipe) is this too high a temp to activate the electic fan and start the cooling???

Any ideas please? Limey
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Old 02-05-2003, 02:22 PM
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I use a black majic fan with temp control.adjustable from 180 to 230 I set it at 180, the instruction that came with the fan recommend that the temp sensor pass thru the radiator close to the return line...on a chevy this is usually the top hose...I use this in conjuntion with a 180 degree thermostat in the winter and a 160 in the summer..cools just fine
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Old 02-05-2003, 04:16 PM
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A good place on small blocks is rite next to the thermostat on the intake on the cross over.

[ February 05, 2003: Message edited by: 1BAD80 ]</p>
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Old 02-05-2003, 04:27 PM
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HEY K: I question the top hose being the return on a Chevy?? It is my understanding that the hot water flows out the top hose to the top of the radiator?? Please correct mr if I am wromg. THANKS DAVE
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Old 02-05-2003, 04:36 PM
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Yes on a standard sbc the coolant flows to the radiator in the upper hose. That is why the t-stat spring is on the engine side not the hoses side of the t-stat housing. Spring warms up, opens t-stat, coolant flows past spring through t-stat into upper hose.
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Old 02-05-2003, 06:11 PM
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Dave- depends on wether he meant return to the block, or to the radiator. :p
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Old 02-05-2003, 06:57 PM
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Dave I was refering to the water returning to the radiator to be cooled...that would be the top hose comming off the block and into the top of the radiator. I should of made myself clearer in my first post.
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Old 02-06-2003, 01:49 AM
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Cooler water comes out the bottom of the rad, so as my sensor switches the fan on at the same temp as my thermostat opens (both about 180) I'll fit the sensor into the bottom of the rad to avoid constant fan running.
Thanks for your help, Limey
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Old 02-06-2003, 01:39 PM
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Just going to put my 2 cents worth iam running same set up as mentioned in above post by kaiserknife and works well adjustable sencor is nice lets you dial in exactly if you have acess to lazer type tempgun you can check at differnt spots top of rad at heads quite intersting to compare locations your thinking i have to much time on my hands NO just a long winter take care :p
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