MPG's and a question

[Doctor CAD]

I bought a OBD2 bluetooth signal sending unit and have a software called HOBDrive on my IPAQ.



I have been keeping track of MPG with it for the past 3 tanks of gasoline. My commute is 8 3/4 miles one way, the roads vary from 45 mph 2 lane to a short stretch of 4 lane 55 mph to stop and go for a mile. I have averaged 18.6.



Over the past weekend, I drove across NC and SC to attend a BBQ festival. On the way there, I did not reset the MPG value and I was showing 19.8 to 19.9 as an average. I filled up and reset the gauge for the trip home. 244 miles of total highway driving. The first 45 miles is 2/4 lane 55 mph rural highway, the second part is 70 mph interstate in SC and the last 45 miles is 65 mph in NC.



I am a +5 to a +8 mph driver (55 = 60 to 63) (65 = 65 to 68) (70 = 73 to 74 because the truck just doesn't like to go much faster than that for long stretches comfortably).



On the 55 mph trek (60 to 63 mph) I was 21.4 mpg, on the 70 mph trek (73 to 74) I was at 20.0 and with the last 65 mph bit, I ended up with a total of 20.3 MPG. Thats with 2 adults and luggage.



I have no roof rack and I am XCal 2'ed to a 87 torque tune (by Torrie).



Looks like the sweet spot would be around 65 mph, but who can keep that up!



OK, now for the question... One of the reported sensors is collant temperature. On the trip, I was seeing 199 degrees for all 4 hours of the trip. I would really like to see that drop to 190 or less with all the airflow over that radiator at highway speeds.



Does it seem like time to change the thermostat and coolant or is that temperature "normal"?



I am going to retune to the 87 economy tune and keep track of MPG's that way for a while, but i really hate not having lots of power and neck-snapping shifts!

 

[Richard L]

I don't think it's the speed that is effecting your MPG, but more likely driving the +5 to +8 MPH over the speed limit might be faster than the rest of the traffic. I have gotten some of my best fuel mileage (22+ MPG) in my Sport Tracs driving between 70-75 MPH which includes quick accerations on freeway entry ramps. But I did most of my driving between 11:00pm and 6:00am. I suspect that the big difference is TRAFFIC.



I also have an Ultra Gauge and found that if you tend to drive a little faster than the normal flow of traffic, you will always be coming up behind slower traffic an you will have to brake and then speed up to get around them. That constant slow-down and speed-up cycle really kills the gas mileage on a heavy vehicle like the Sport Trac...especially with adult passengers and luggage which can easily add another 500 lbs to the overall weight you are trying to accelerate.



I find that if you find a large opening in the right lane and set your cruise control to just at or slightly below (-1 MPH) slower than the traffic in that lane...you can drive for extended periods of time without having to slow-down and speed-up to so much.



When I travel at night and in the wee-hours of the morning, there is very little traffic and you rarely have to change your speed. I drove from Waco, TX to Zanesville, Ohio (about 1200 miles) and I left at 11:00pm and I don't think I had to touch my brake pedals, or slow down more than about 3 times until I stopped for gas which was over 430 miles later.



You also need to condsider the wind and if you are bucking a head wind, the faster you go, the more gas you will use. Unfortunately, you may not have that same tail wind on the return trip and so you cannot always assume that you will gain the mileage back on the return trip.....There are just too many other factors involved in gas mileage that you cannot control.



It's always best to keep the vehicle in good running condition, keep the tires inflated about 4-5 PSI higher than the inflation sticker calls for, and especially watch your driving habits. I found that a $60 investment in an Ultra Gauge really has helped show me where I am loosing gas mileage and where I am getting good gas mileage. Now I can drive under most normal conditions and get within 1 tenth of a MPG of my best MPG average.



....Rich

 

[Johnny O]

Cooler is not necessarily better. Modern engines are more efficient running at higher temperature.

 

[Todd Z]

The Sensor for coolant is right at the T-stat in the Flow driection....



The ST uses a 195 degree T-stat. SO IF you held 199 I would say that sounds normal to me....



My st runs around 198-200 in slow traffic on hot hot days, and ac on, i may hit 208-210 which is perfectly fine.....Until i start moving again...



IF you run a cooler t-stat you need a re tune for it........



I plan on running a cooler one when i change mine at 120,000 with my coolant..... ( i do coolant every 60K)



Todd Z

 

[Doctor CAD]

5 to 8 over the limit is not much faster than the normal flow, but you are right. Slowing down even 2 mph has a dramatic effect on MPG.



I use my cruise control a lot. Even on rural 2 lane roads.

 

[Richard L]

doctorcad,

It's not the slowing down 2 MPH that cost you the gas mileage, it's accelerating those 2 MPH when you resume your speed. Even little undulations in the road or barely perceptable uphill climbs will show the drop in gas mileage...as much as 3 to 6 MPG during that time.



...Richard