Scratching my head here with MPGs...

[turbo98]

Ok, this is gonna be long winded.

I work out of my truck(pro-4x) I bought it with 5 miles on it on November 23rd and I currently have 3562 miles on it. I average a tank of gas every 1.5 days. I have tested MPGs in every situation and speed by tank/miles. I have found that the oem computer is fairly close in its estimates. It's gets off the better your MPGs get. I'm gonna list the speed I traveled and how many miles and the MPGs I am getting, then I'll explain my problem:

Cc set at 78mph for 232 straight miles= 17.4 MPGs

Cc set at 73mph for 182 straight miles= 18.7 MPGs

Cc set at 70mph for 182 straight miles= 20.3 MPGs

Full day of idling with short driving through dirt roads, 47 miles of hwy use set at 73mph= 13.4 MPGs

Full day of 4x4 use, speeds not exceeding 30mph and by all day I mean 6am to 4pm= 8.1 MPGs


Now here's my problem. My MPGs have considerably dropped. I drove 232 straight miles with the cc set at 75mph and I got 15.8 MPGs. My all day idling MPGs have dropped to below 11 MPGs. I haven't changed a thing. My only guess is maybe the oil is getting thick and causing sludge, thus straining the internals?

Anyone have any suggestions?

[turbo98]

Also, these miles are pure interstate, not slowing down at all. I have all kinds of results I can post. I keep a log of every tank and speeds I kept during that tank. This would be a good thread to sticky for reference. I drive from Jackson, MS to Mobile, AL every weekend and from Jackson, MS to Birmingham, AL every other weekend. My daily drive is 47 miles one way to work by interstate. I stay on dirt roads and country back roads all day at work. My truck averages about an hour of off time while I'm at work. Other than that, it runs all day, non-stop.

[kgordon]

I would discount sludge. At a hair over 3000 miles your oil would be fine, i changed mine at 3000 after i bought it brand new and the oil was the same color as it went in. You could change your oil but thats up to you. Your engine was just breaking in so possibly you received higher mpgs during the break in? Though usually its the other way around.

Not sure where your located, if your in a cold climate have you checked your tire pressure? The sensor does not warn you until 5psi below normal I believe. Also the gas companies have switched to winter gas which provides you with fewer mpgs. Just a couple thoughts i have. But it wouldnt hurt to check your fluids just to be safe.

[Delta]

Originally Posted by turbo98

I drive from Jackson, MS to Mobile, AL every weekend and from Jackson, MS to Birmingham, AL every other weekend.

Seems you're spot on with that mileage (I assume the 232 mile is that trip) I can drive roughly the same stretch (although Meridian, MS to Gadsden, AL) and average a little over 18 with mine being 2wd. This was last week, so it was winter blend gas... So your 15 sounds about right being 4wd and not "broken in" yet.

Also idling alot will most definitely kill your mileage, as being in 4x.

It had puzzled me all of a sudden as well going through my notes. As I got further in the mountains my MPG went up. Last fill-up netted me 21.35 in the mountains of Virginia

[turbo98]

I'm scheduled at the dealership this Saturday. I'm following the owners manual for "severe" use and changing at 3750 miles. My temps have averaged about 50 degrees here. I also drive normal. My revs average 3k rpms until I get to my desired speed. My tire light comes on every morning until it warms up, then it turns off. I need to mention I have a Volant intake as well. I've had it since it was new.

Originally Posted by Delta

Seems you're spot on with that mileage (I assume the 232 mile is that trip) I can drive roughly the same stretch (although Meridian, MS to Gadsden, AL) and average a little over 18 with mine being 2wd. This was last week, so it was winter blend gas... So your 15 sounds about right being 4wd and not "broken in" yet.

Also idling alot will most definitely kill your mileage, as being in 4x.

As I agree, I need to remind you that my mileage is getting worse, not better. I was getting 20mpg when I had a little over 1500 miles on it. Now that I have 3500, it's down to 15ish. I'll be traveling to Mobile this weekend and I'll update with my mileage.

[Delta]

If you're actually going off your gauge, that's not the most accurate method. Try a couple tanks hand calculating it and see what happens.

[JeniorNV]

Originally Posted by turbo98

My tire light comes on every morning until it warms up, then it turns off.

Bump up your tire pressure!

[turbo98]

It's got nitrogen in them. It's a pain to add pressure.

Originally Posted by Delta

If you're actually going off your gauge, that's not the most accurate method. Try a couple tanks hand calculating it and see what happens.

I ONLY calculate by hand. As stated earlier, the trip computer is close, but it's not 100%.

[JeniorNV]

The tire pressure light comes on when you are below 28 psi. Check your tire pressure the next time you see the light come on. I would think a 2-3 mpg loss could be explained by a combination of winter blend gas and underinflated tires. I see a 1 mpg or so drop every winter with my tires set properly.

[turbo98]

I will def. check them. The light is on currently.