I'd like to hear some feedback on what outdoor temperatures give you the best MPG cruising on the highway.

May sound crazy, but I was also an original Honda Insight owner, where MPG is an obsession, and we found that with that non-turbo gasoline engine, with hot, dry weather gave us much better MPG than cold weather. On a 90*F day, I could squeeze 60-61 MPG out of an entire tank-load. But in freezing cold, dry weather, I'd be lucky to get about 54 MPG and had to work even harder to keep it there.

But my Excursion seems to be doing the opposite. Crusing on the highway, I can re-set the overhead computer and get 16-18 MPG at 65MPH when it's 60-70* out, but having a difficult time keeping it above about 14.5 MPG on days in the 80s and 90s.

Experiences?

 

This will be interesting, Lots of things come together here. colder air is denser so has more oxygen per cubic ft, so more power. But also harder to move through. Also there is the summer\winter fuel thing going on. Who knows, but some real scientists on here will probably show up with actual data that only they understand, but you can usually get the jist of what they are saying. That over head computer isn't real accurate usually, although mine was pretty close until I put tunes on the truck. Thats all I know which might not be right anyway. So just hang out and see.

 

There's a couple of other things that come into play.

Insight: MAF system with 2 O2 sensors. The general thinking here would be, colder denser air would be measured by the MAF and other instruments and provide more gas to mix with it. More HP, but also, worse mileage. And yes, colder air is more dense. + MAFs are really accurate at reading load.

7.3L PSD = speed density with MAP and IAT and no O2. (I was a bit shocked when I figured out there was no O2 when I replaced the turbo-back with a 4")

Not sure why it would be different, but the MAP is only measuring pressure in the manifold. And no O2, to trim things as they go, means, there's some pretty static tables in the ECU that are not very dynamic...not as much as they would be with a MAF and 2 O2 sensors. They only change based upon IAT and throttle position and MAP, and try to guess load.

I am running on B100 that is from rapeseed (I also can get yellow grease-based if I want)

 

Winter diesel contains far fewer BTUs than summer fuel so you'll see a big difference in winter vs summer fuel mileage.

Past that I'd hand calculate again if I were you and I'd be willing to wager that the difference in economy varies more by driving style than by temperature.

My mileage drops by around 1-3 mpg in winter and in summer I get 13-15 depending on driving style and what I'm hauling/towing. Worst I've ever gotten in this truck was just above 12mpg.

 

Beats me man, this mpg thing goes around all the time and seems to come down to good maintenance, clean fuel, summer/winter fuel, and consistant good driving habits. and then all the things you might not notice, like a head or tail wind.

 

I agree with everyone, I need some more comprehensive comparisons. I was looking to see if there was a well-known answer to the question or not. For the Hypermilers on the Insight forums, it's a well-documented phenomenon.

But just so everyone knows, I am using Biodiesel B100 that is not home-grown, it adheres to ANSI standards. Thinking they don't have different winter/summer blends of B100, but not sure.

But in any case, the fuel blend would not matter. In California, you cannot buy B100 from a pump that has an underground tank (so most service stations don't carry it) so I bought a 275 gallon tote, bought some from a distributor, and pump at home. The loose comparisons I've been doing on cold and hot days are from the same batch of B100 fuel, and in Northern California we are having alternating weather of 55-65* and then warm 85* days, all in the same week.

The fuel is made by Golden Gate Petroleum | San Francisco Bay Area.

 

hey, I didn't get that you were only running bio. Can't comment on that, I've never used it. Isn't that hard on sealing components like o-rings and sealing compounds in older diesels like ours? thought I heard that before.

 

Don't mean to sidetrack the thread, but to address your question, our rigs are B100 compatible. Some time in the early '90's most automakers went to Viton fuel components, (i.e. hoses, seals, o-rings, etc.).

 

really? I thought they were buna, thats why Riff Raff and Diesel O-Rings sell viton replacement sets. No?

 

LOL .... Good Luck

 

Perhaps I stand corrected. Care to elaborate?

 

After dealing with the o-rings and seals in these truck on a daily basis for over 8 years and speaking with 100's if not 1000's of customers and the problems that they have had in the past and currently; along with long discussions with DuPont engineers, the o-rings that International used in building these engines are not Viton. They are Buna-N (aka Nitrile). A common elastomer that has been used in the automobile industry for many years. They worked just fine in these Diesel engines until the early days of Low Sulfur Diesel.

The primary example and most obvious is the drain valve since it is the weak link in our fuel system. It is the only dynamic seal in the fuel system. When the drain valve o-rings become fuel permeated, the elastomer actually changes its chemical characteristics where it will begin to SWELL AND SHRINK with TEMPERATURE changes. This is why the drain valve will commonly leak in the mornings in the winter months and as the engine warms up, the leak will slow down or actually stop leaking until the engine cools off again.

Viton can swell slightly if attacked by certain compounds such as strong base, high pH, caustic aminos, MTBE, MTK and some other nasty chemicals but THEY WILL NEVER SHRINK let alone with temperature changes. This is only a characteristic of Buna-N when attacked by ULSD additives.

The only true Viton part found in our fuel system is the Fuel Pressure Relief (regulator) seat. It will remain un-effected with over 200,000 miles of fuel flowing past it. It will not be swollen or slimy like the CCV o-rings become over a much shorter period of time.

The hoses that International uses in the OBS (94-97) trucks do have a generic Viton (non-DuPont) liner. Fuel is not the culprit that causes these hoses to degrade but rather it is the constant heat exposure that they are subjected to in the engine valley.

 

As a matter of fact, I believe you did point out some of the incompatible seals in another thread a couple years ago. I had forgotten about that until now. I suppose since I have been running B60-B100, (mostly the latter), for over 30k miles in the last 4 years or so without any leaks......yet, I haven't given it a second thought. (Surprising to me given the number of times I've flipped open that drain valve).

Bob, you can be sure to be receiving an order from me in the future when I get to re-sealing my fuel bowl. Thanks for the clarification.