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Meph 07-25-2010 02:15 PM

Thermo Fan Settings
Hello Again,

Once again trying to squeeze out some more MPG from Toyota Powered Datsun.

I run an after market ECU so i can control all the variables, so my next tuning stage is to get my thermo fan on at the right times. Right now its on at 192 and off and 186, but I think this number is a little low, I believe my thermo opens around 185, the standard one.

MY temp is always at 189-190 so the fan is always on when Im driving (overlap between the thermostat and fan settings im guessing), i think over time this extra current draw will hurt gas mileage.

would it be safe to run the fan at say,


Id hope to get to a point where the fan doesn't need to be on and lets the rad and airflow do the work.

whats the school of thought for a decent on off setting?

Thanks a lot!

RobertSmalls 07-25-2010 02:45 PM

You should probably set it a bit higher than you have it. My car turns on the fan 10F above the t'stat fully open temperature, and turns it off around t'stat +3F.

The radiator fan should come on only very seldom. If it's still on all the time after you raise its set point, then you need to open more of your radiator grille. If it never comes on, then close more of your grille.

ShadeTreeMech 07-25-2010 03:05 PM

you have a toyota powered Datsun mentioned, but a celica listed (cool car, btw)

What datsun are you talking about?

I wouldn't worry about the rad getting hot til about 200 to 220, which is where most OEM fans turn on, I believe. 192 is rather cool for the fan to turn on; a healthy cooling system will tolerate up around 230-240 with no ill effects. Keeping the engine that cool also cuts into the mileage; the fan pulling the extra amps olnly adds to the problem.

I would try a on setting of 210, off at 205. Assuming a healthy cooling system, this is well below its specs and you should see a boost in economy as a result.

Meph 07-25-2010 04:28 PM

thanks for the inputs,

I use to have the 89 celica, due to e-tests it had to go, took 9 tests to pass because it was running too good! (high nox) wasnt going to go through that again 2 years later so I sold it. Got on 98 impreza, lots of fun int he winter and gets about the same or a little better mileage.

The Datsun is a 73 Z with a toyota 1jz-gte single turbo engine, final goal is 300hp, 30 mpg but i think i have a long way to go still (mileage wise, power is there :D)

I've programmed 205 and 200 for now till I get a few more inputs, there's also a Ignition coolant Map that will advance or retard ignition in relation to coolant temp, I will start pulling ignition timing once the temp is beyond 210 deg, it was set to start reducing ignition at 200 (by me) but if im crossing the line i'll start later on.


wriley4409 07-26-2010 02:16 AM

Chevy LS1 electric fan setups usually turn on the fans at around 226 degrees and off around 215 degrees.

EdKiefer 07-26-2010 10:18 AM

I would try 210 -215F for fans on . Thats still on low side for OEM specs, many vehicles go a bit higher than that too .

comptiger5000 07-26-2010 10:56 AM

My Jeep has 2 thermo switches for the fan, 1 in the upper rad hose for low speed, one in the lower rad hose for high speed. Each switch kicks on at 210*, off at 207*. This leads to actual gauge temps of:

Low speed on: 214*
Low speed off: 211*
High speed on: 220*
High speed off: 217*

There is also a pressure switch in the A/C system to activate the fan on low speed when the A/C condenser isn't getting enough airflow to keep cool.

The fan on mine is the factory 16", 2 speed E-fan based off the Ford Taurus 3.8 fan and similar to the larger Lincoln Mark VIII 18" e-fan.

For yours, I'd say on at 210*, off at 205* would be a good starting point.

Daox 07-26-2010 11:08 AM

Why not look up what the stock settings are and go with that?

Phantom 07-26-2010 12:23 PM

Place a light in line with the fan that will let you know when it is on and slowly adjust the temp setting to where it only comes on when sitting in traffic as when at speed it should not be needed. The 205-200 should be good but it you notice that the fan keeps turning on and then off then back on you might want to set the temp difference a little further away such as 206-198.

My NA 3800 v6 has a t-stat that opens at 195F and the fans are set to the following.
Ambient temp (measured in air intake) 122-119.3F
Fan 1 212-208.4F
Fan 2 221-217.4F

EdKiefer 07-26-2010 02:31 PM

You just need to make sure fan turn on is above thermostat full opening temp by at least 10F IMO. You don't want fan to be fighting with thermostat .

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