Towing Mileage

[Caster]

Update on my towing experience. Completed a 680 journey between Phoenix and Palm Springs towing a single axle 3,600# travel trailer. Outside air temperature range 85-95, speed at 68 MPH, 1,900 RPM, transmission stays in 7th, 8th or 9th gear depending on grade. I switched between Tow and Normal modes. Milage did not differ. Averaged10 MPG. In the city, pulling less than 45 MPH, getting 15 MPG. Highway speeds dropped to 11 when the outside temp was in the 70s and then dropped again to 10 at 80+ degrees. The ST still has huge acceleration pulling this weight trailer, it just sucks lots of fuel.

Adding the large inter/after Whipple cooler did not change the milage. Bottom line, if you are pulling weight, your gas milage is going to be 10 MPG. My normal in city driving MPG is 21.7 using 87 octane. Note: I tried 89 and 91 octane on the trip, no difference in MPG.

10 MPG with a 21.8 tank capacity means stopping every 2.5 - 3.0 hours. If you are old man, all this stopping may work well. I have a 1,900 mile one-trip coming up shortly so with gas at $5.00 / gallon, that means $950 one way. Yikes!

I understand this thread is months old but I'm going to ask what I feel is already obvious..! Adding the larger intercooler for any towing purpose was to no benefit other than lightening your wallet?

 

[CoHPhasor]

I won't speak for others here, and I have not towed yet. (Actually, I'm towing tomorrow for the 1st time, a 6x12 Uhaul with a few pieces of furniture)
- Intercoolers help keep charge-air temps down.
- The combination of charge air temp and octane, help keep your engine from knocking
- When the engine knocks (imperceptibly to humans), the engine retards the timing and makes the air/fuel mixture more rich

Now, is running an IC or the highest octane fuel you can buy, necessarily going to increase your gas mileage? That depends on many factors.
Here's what I can say: On long trips through hot areas, it does not hurt to have a larger intercooler.
(Some may not feel it, especially on flats or downhills because there is a lot of air rushing over the intercooler at speed, when not following people closely)