Wish I had a Scangauge years ago...
 

The scangauge is a great tool! Its showing me some interesting things besides the obvious best speeds to drive at for higher FE.

-Driving on roads that have 3mm standing water really eats into your FE! I often see 6mpg drop that can last for miles? Time to pick a better road when its raining heavy. What can I say, Louisiana roads are terrible...

-When your roof rack is literally whistling in the breeze its likely costing you FE.. Yep I removed the roof rack and it looks like it was good for 1.5mpg at speed. Nice!

-My engine is not getting warmed up near fast enough especially in the morning. Looks like 190F is where it eventually controls at if you drive long enough. Now in the morning all it ever gets too is 186F. I really can see a difference in FE when its running under 190F. I think what?s happening here is the radiator is over cooling the water keeping a good portion of the engine running too cool. I?ve got a thermostatic fan clutch so its pulling air at all times. One morning I ran the A/C for a short time to help heat the water then shut it off and sure enough the steady state mileage numbers jumped up to the range where there supposed to be when fully heated.
I?m really thinking about an electric fan conversion? Next thing I?m going to try is block off the bumper air intakes and see what that does?

Last fill up was 25.3mpg, not to shabby for a EPA combined 18mpg truck!

Gratz on the FE jump ! I am amazed at the increases that the truck folk get - I've had two myself and never could get the bump like I'm seeing here . Quite an accomplishment!

IFE *is* the greatest thing since sliced bread idd'nit ? You really 'see' what you are achieving and know what works right away .

Good information. I've often wondered how much standing water effected FE.

I would recommend blocking off the upper grill and leaving the bumper air intakes open. I would also get an electric fan for the radiator.

I would try the grill block and maybe some of the bumper air intakes block, first, as far as engine temperature goes, before you change something. I suspect your thermostat is probably starting to open at around 186 and the air which is being pulled through the radiator, right now, is what is keeping it from getting up the last 4 degrees.

iirc ridge riding gets you out of the wear ruts in the road and helps keep you from plowing through rain water (or light snow for us northerners).

Good thinking. The far right lane on the interstate has deep ruts from all the semi's, but you'd have to see if your car is wide enough to run the ridges,,,

I try to run on the ridges in the road but its a narrow two lane road with no shoulders.. It puts me almost in the ditch or into oncoming traffic so now I just avoid that route when its raining..

Oh yea! I used to run whole tanks trying a specific driving style to see what works better.. Thats like working with "Stone knives and bearskins". :D

The lower bumper looks to be way easer to block from the back side so thats they way I'm going first. Also in states with front plates it would block over half the bumper inlet so I think its mostly for show...

I had looked up the thermostat specs in my Toyota service manual and it has the thermostat fully closed at 104F, opening between 176-183F and a valve lift of 8.5mm or more at 203F. So I was thinking it seems to be in the ball park but I need to do some checking to see if its leaking to bad.
I have an IR thermometer but have not checked what the radiator differential temp is nor the engine outlet. Its on the list of things to do. From some internet sources I found the radiator is only supposed to drop the water about 10F so thats another thing I want to look at.

I need to find an old Ford Tarus fan or a Mark VIII. Going to call some junk yards after the 4th.

Wow - 25.3 mpg- excellent for something rated 18!

Only 186 deg showing on ScanGauge?

Replace your thermostat. Try learn what's oem spec and get one rated that temp, or maybe hotter. T'stats can lose their calibration over time and not keep things at the intended temperature. Also an independent shop may well have replaced the original with one calibrated for another temperature.

Yes - grill block and other things can help but the t'stat is supposed to get the engine to proper temp and keep it there.