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Auxiliary Fan Question


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If he's got a PDC it's an HO. The aux fan is controlled by the ECU by applying a ground signal output from pin 31 to the coil of the aux fan relay in the PDC. This ground signal is generated by the A/C turning on, or by a high temp signal from the sensor on the thermostat housing. OR by a simple dash switch that applies a ground to ECU pin 31. That's what I use as a fail-safe in my two electric fan setup. :D

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I was thinking about an electric aux fan.

flex a lite recomends a pusher fan.

btw, what is too hot anyway?

I run 220-230 in traffic.

 

BOB

 

that high. just over the danger zone of too much head flex-age. id put a lower temp thermostat. i run a 160 in my stock 350sbc truck and suprisingly my fuel economy went up? whatever. 220 isnt deadly but tis not good for the motor

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230 is a little hot. But you should run a 198* stat and you should see about 210-215* at the head... The factory gauge is not accurate typically, so you may not actually have any issues.

 

Swapping in a lower stat is not right. The EFI is supposed to run warm/hot or it will have more issues.

 

X2 on the stat. The factory gauge tolerance is + or - 5% new; after 20 years it's good to have a 12% tolerance after the sensor or switch probe is calcified and corrosion has created additional resistance in the temp gauge circuit. If you have 210-215* at the gauge sensor (or switch) verified by a known accurate external infrared or laser thermometer, you're golden.

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Most guys eff it up. They look at the gauge and assume A)It's actually accurate B)That's the temperature of the entire head C)It's a problem that it's warmer than the typical 1970s carburated chevy runs.

 

 

Time and time again I see people swap in 160* (or pull) tstats to fix their 'running hot' problem, only to find that the engine runs like a pile of $#!& and fuel economy goes to half. If you screw it up bad enough, the computer will never come out of closed loop (warm up mode), and it'll run pig rich 100% of the time. Or, if you screw it up a little it'll take longer to come out of closed loop, and settle at a temperature that is not optimal for combustion. The ECM and fuel injection was designed and programmed with the intention of it running fairly warm. The OEMs figured it out long ago that they could eek more power and milage that way.

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The factory gauges are crap Dirty (as you know). Cheap, inaccurate, mass produced, and only get worse with time. I calibrate these things, and I'm still amazed how far off they are, not only the temp gauge. As has been posted ad nauseum, the 4.0 runs best at 210-215*. Best performance, mileage, and reliability. The 195* stat combined with a healthy cooling system is still, and always will be, the best solution to overheating problems. A lower temp rated stat does nothing, except delay open loop operation, compounding problems. Before throwing pieces and parts and $$ on the cooling system, verify the actual temp at the gauge sensor first with a know accurate external thermometer. Then go from there.

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which is why i had a question mark after my statement. it just dosent make sense

Is your Chebby 350 injected and computer controlled, or "old school" carburetor and distributor? Back in "the good old days" we always ran colder thermostats than the factory, and got better performance and better fuel mileage. Probably didn't help emissions much, but testing was rudimentary back then.

 

The Jeep computers don't come out of open loop (warm-up) mode until around 168 degrees, so running a 160-degree t-stat is indeed (as explained above) likely to result in a truck that runs "pig rich" all the time. Since the purpose of a thermostst is to keep the temperature UP, not down, there is no reason whatsoever to run a colder t-stat than the factory 195-degree. Let's face it -- if your radiator is so fubarred it can't cool the engine down to 195, how do you think it's going to cool it to 180 or 160?

 

Also, be careful in reading that factory gauge. Aside from the tolerance, remember that it does NOT read on a linear scale. I see posts like "My Jeep runs at 231.3 degrees" and I wonder "How the hell can you read that gauge to any semblance of precision?"

 

"Cold" is marked as 100 degrees. Halfway, or straight up, is 210 degrees. So the first half of the needle's range is 110 degrees. "Hot" is what -- 280 (IIRC)? So an equal swing on the upper end of the scale is only 70 degrees. So the needle isn't on a linear scale, folks. Good luck guessing what it's actually reporting if it's anywhere other than right on 210.

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which is why i had a question mark after my statement. it just dosent make sense

Is your Chebby 350 injected and computer controlled, or "old school" carburetor and distributor? Back in "the good old days" we always ran colder thermostats than the factory, and got better performance and better fuel mileage. Probably didn't help emissions much, but testing was rudimentary back then.

 

The Jeep computers don't come out of open loop (warm-up) mode until around 168 degrees, so running a 160-degree t-stat is indeed (as explained above) likely to result in a truck that runs "pig rich" all the time. Since the purpose of a thermostst is to keep the temperature UP, not down, there is no reason whatsoever to run a colder t-stat than the factory 195-degree. Let's face it -- if your radiator is so fubarred it can't cool the engine down to 195, how do you think it's going to cool it to 180 or 160?

 

Also, be careful in reading that factory gauge. Aside from the tolerance, remember that it does NOT read on a linear scale. I see posts like "My Jeep runs at 231.3 degrees" and I wonder "How the hell can you read that gauge to any semblance of precision?"

 

"Cold" is marked as 100 degrees. Halfway, or straight up, is 210 degrees. So the first half of the needle's range is 110 degrees. "Hot" is what -- 280 (IIRC)? So an equal swing on the upper end of the scale is only 70 degrees. So the needle isn't on a linear scale, folks. Good luck guessing what it's actually reporting if it's anywhere other than right on 210.

 

yeah i have a q-jet 650. i always was taught from tech's and teachers that a tstat fully open at 210 is about as good as it gets. well i go play in the mud for hours on end and radiators get glogged up so i though well. i have to replace the tstat anyways so ill put in a 160. well i did and tada. everything you just said. it hasnt hit 210 since i put it in. it seems to be around 160-175 just above halfway when the stat is closed. i can watch the guage go up and then go down slightly

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about halfway down this page (see link)

flex-a-lite says fans used as an aux should be a ousher.

primary fans are pullers.

 

Yes, I see it. Those are just general statements unspecific to any vehicle make or model. It also states that pusher fans are less efficient than pullers. So why would you want a pusher? And where would you mount it on an XJ/MJ, especially if it has A/C? Out in front of the grille? :eek:

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