Discussion in 'Performance' started by swathdiver, Oct 10, 2017.
+1M for that save!
We'll start with a 2" level.
Refueled, harassed my daughter at her job (Panera Bread) and bought some cheese curds at Culver's for my other youngin'. Mileage was hanging around seven and the alky content was all over the place so we hit the highway for two exits, turned around and went home. At 65 mph she did a one way average of 20.4 mpg. Alky settled to 8%, 1 more than the last three tanks from the same station. For those not familiar with my previous experiences, that is awesome! Awesome for a 7,000 pound 4x4 truck with LT tires on all 8 cylinders!
Last tank averaged 10.8 mpg which included probably 6 or seven hours of idling, at least and that trip into the swamp and woods with the kids. Been waiting to do the datalog at night when its cooler, at least in the 70s but it was 86 out tonight. Felt good though. Truck is filthy, needs a good cleaning and wax bad. Impatiently waiting for fall weather! Who wants to come over and claybar and pick rocks out of the treads? My wife is a great cook!
It's been about 12k miles since transmission fluid was changed and the internal oil life monitor says 92%. Almost 3k miles since the oil change and the OLM is showing 77%.
Did the datalog for BlackBear tonight and then a mileage test running two way averages again in 5 mph increments on 3 different roads to stay within the law. Picked what appeared to be flat roads but sometimes the difference one way was 1, 2 or 3 mpg. With up to 5 runs per increment, here's the averages so far:
35 MPH = 23 MPG
40 MPH = 23.4 MPG
45 MPH = 21.8 MPG
50 MPH = 21.6 MPG
55 MPH = 21.2 MPG
60 MPH = 20.8 MPG
65 MPH = 19.9 MPG
70 MPH = 18.0 MPG
75 MPH = 17.2 MPG
80 MPH = 15.4 MPG
So there appears to be a big falling away after 65 mph. The spread between E85 and gasoline gets tighter the faster one drives too. It would really pay off at speeds 80 and above! I still think the 70 mph segment could improve, I've seen 18.5 at that speed before with seven hundred pounds more weight in the truck before.
I noticed tonight that between 75 and 80 she felt very composed and tight, almost like running on rails. Those crazy LT tires finally evened out temperature wise once at 70 and above, 51 psi all around. Below that they are all different.
Why is the mileage falling away so sharply at 70 MPH compared with 65 MPH? I cannot put my finger on it. A worn bearing on an accessory? There was a noise last month that we heard twice but has not returned. No misfires, no leaks, fuel pressure is fine, all temperatures are fine.
Speaking of temperatures. Spent a little over 6 hours behind the wheel today. First leg was to pick up my daughter from school. Paid attention to temps more closely but left note pad in the truck. Highest speed was 45, most of the time spent a 35 mph. Highest ECT was 196, highest EOT was 210, highest TOT was 180. Next leg after this tanked the mileage during rush hour stop and go and temps all peaked slightly higher. Mileage went from mid 14s to mid 12s.
Hit the highway and she would not deliver better than mid 14s @ 70 MPH for while. Then she crept up to 16. At 75 MPH the EOT was in the low 220s. More idling, city driving and then back on the highway for the return leg. MPGs averaged 18.6 @ 70, still low but better than earlier. ECT was solid at 192, EOT didn't budge off 217 and the trans was it's usual self, in the 150s, I'm forgetting already.
The reason for such attention to the temps is that I am considering installing a lower temp thermostat in order to run a lower viscosity oil, like 0W30 or 0W20. And the reason for that is to gain in highway MPGs but not at the expense of durability or reliability.
It was hot and humid out today, the truck acted like my old Buick's on such a day, no power. My daughter said the same thing about her little Kia. Temps said high 80s and 91 or 92 but maybe it was the humidity.
The idiot light is on and this tank is done. Switching off Chevron for Mobil. It's less expensive and more widely available around here. After a tank or two I might switch to 89/91 and see how she runs on that. I miss E85 though, just not the short legs.
Last 4 runs at 65 mph were 20.2, 20.4, 18.9 and 20.2. For of you in Rio Linda that's an average of 19.9 mpg.
Last six recorded runs at 70 mph were 18.5, 17.2, 17.8, 18.5, 18.1 and 18.6. Average of 18.1
The difference in MPG between 40 and 45 is 1.6.
The difference in MPG between 45 and 50 is .2.
The difference in MPG between 50 and 55 is .4.
The difference in MPG between 55 and 60 is .4.
The difference in MPG between 60 and 65 is .9.
The difference in MPG between 65 and 70 is 1.8.
The difference in MPG between 70 and 75 is 1.0.
The difference in MPG between 75 and 80 is 1.8.
What say y'all?
Driving with your engine in its ideal power band sweet spot makes a big difference in mileage as well.
What's a 5.3 LSs sweet spot? I had a Pontiac that got better mileage at 77mph than at 70 or 75. At 90, it would return the same mpgs as 70 or 75! That little VVT motor loved to spin.
In general there is an ideal place where the power output of HP and torque is ideal at the right rpm that will produce the best fuel economy for the gearing you have and tire sizing you had. I had always thought it was the speed limit of the highway system at the time of manufacturing. So if i made changes to gearing or tire size the goal was to still maintain the same tire revs per mile along with the same engine rpm therefore maintaining the ideal mileage ability for the speed limit. maybe that explains it. Or maybe that is useless info as well.
I hear ya. What I find odd about the 2mpg drop is that that did not happen with while burning E85. It was .8 mpg.
Here's something else. The mileage figures posted are really for the 3.08 geared trucks. The XFE trucks were also 3.08 geared and squeezed out 22 mpg.
So that being said, at 70 mph a truck with 3.08 gears equipped with the 6-speed is turning about 1500 rpms. Well, guess what mine is turning at 65 mph? Just over 1500 rpms too. My motor was the year before VVT and that seems to have added a solid 1 mpg on the highway for those engines. So with my AT tires, 3.42 gears and single pattern camshaft and AFM turned off with a tune, it could be worse. It just seems odd to me that there is a big step if you will in loss of economy and then it is more gradual again at even faster speeds.
This morning's run showed something else, the fuel trims at idle or when stopped in traffic climb. At idle they'll go to -13, this is LTFTs. But at speed they'll go to zero or thereabouts. I wonder if that's an indication of my intake gaskets leaking or just the tune?
Ok James... school me...
What is the purpose of a lower thermostat with a lower viscosity oil???
I have considered changing to a 0w20 or 0w30 oil as well and never gave a thought to changing the thermostat.
A 0w30, at operating temperature, would effectively be no different than the 5w30, at operating temperature, we are running now.
Also would we need to account for the thermostat change in the tune?
Would the ECU ever get out of open loop if it didn't "see" the engine was up to temperature?
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