I have a dual efan rig on my truck- and one finally gave up the ghost.. this is fine, as I always looked at the things as consumable, and put two in there (one pushes, the other pulls; they overlap about 3~4" or so) in the case this very thing happened..

losing approx 2800cfm of air through the right side of the rad raises temperature a bit.. it's not that I come close to overheating with the other (also 2800cfm), but it ran longer and rose higher than I am used to seeing- so, I put the reader on it just to see...

I run a 180 stat.. instead of running between 178* and 184* no matter what, I found myself running around 195~200*... I'm sure if I had been stuck in traffic or some such, I would have saw higher.. but I didn't.. alright, enough of that.. here is the discovery:

fuel trims dipped as temperature rose, and they leveled out a touch lean- running about 15:1 a/f.. with that, economy floggin' soared.. I ran a full tank through it, even though I've got a new replacement fan in the box- just to see..

it figured in just shy of 15mpg mixed driving...

before you fellas go to doubting, realize I live at sea level, and on flat lands- and rarely see 3kRPM.. I maintain around -15psi vacuum and try to maintain it somewhere below -12 at any given time.. This isn't to say I putt around, though, I usually pull traffic behind me from stops and hold my own at highway speeds..

I also think the true isolated cold air intake (almost RAM air) plays a role, but I don't know that to be true, though.. What I do know to be true, is that engine, running just 15~20* hotter, and up where the OE intended it to run, accounted for some extra MPG's in whole figures.. go figure, huh?

There is some reasons behind this, but I'll leave that off unless somebody asks..

point I'm trying to make is for y'all running efans: crank your controller up some and reap the same benefit.. set that rascal around 195* which should ensure you won't pass 200* before the efan does what it's 'sposed to do..

I'm not surprised it saved some fuel and had little if any impact on performance, but I AM surprised at just how much impact it had..

 

Weren't you running rich because the pcm wants 195 and tries to make that temp? I am curious what your mpg is going to be when you put that fan back in

 

Makes perfect sense. Hotter temps at the intake means leaner mix = higher MPGs/less HP. Cooler temps at the intake means richer mix = more HP/lower MPGs. Although IMO the difference would be minor UNLESS we are talking the difference in temps is enough to make a difference between running open loop vs. closed loop, in which case I would expect to see a real measurable difference...

 

I didn't want to go into the isolated cold air thing, but in short: my air intake temps are often 100* cooler than engine temperature.. it was never more than 50* or so difference without the isolated cold air and functional scoop.. that thing makes a difference... the only real difference it makes is denser air.. I'm willing to wager the PCM is ignoring that IAT at this point..

the leaner burn is documented.. I usually run slightly rich- like, 14.2~14.4:1 a/f.. running just 15* warmer engine/coolant temperature has bumped me to 15.0:1 a/f.. it is without doubt base on the temperature alone (no other variables in play), and it is absolutely related to the trim..

the surprise i found was that 15* makes that big a difference..

I'm tuned via SCT custom tune for all my mods, to include the lower intake temps and the 180* stat... I'm guessing that there is a step in the PCM that the SCT liekly doesn't address that alters trim values based on operating temperatures higher than the SCT thinks it will see..

I don't know that for sure, but I highly suspect it..

Who here has seen the actual tables output/data from a PCM? I know for a fact Sean only manipulates tables and factors he needs to, and leaves the rest alone..

I'd like to hear from other members if they can/would/will alter their efan engagement setting to a few degrees higher (195*), and watch their trim levels to see the same thing I am..

it's just a curious situation..

tonight, I'm rigging the replacement second fan.. I've gotta tow tomorrow, and I ain't risking that engine effin' up just when I got it where I want it.. I fully expect to see the loss of economy UNLESS I adjust the controller to engage at 195*... which I think I will, quite frankly..