15.8mpg in '98 Z71?

RT8 · January 19, 2006

I've read old topics here until my eyes are hurting but haven't come up with a consensus, so here goes:

'98 K1500 Silverado extra-cab, regular bed, Z71, w/350 & auto w/OD

100k miles

I bought it 3 weeks ago, bone-stock as far as I know (still has single exhaust on it).

Service Engine Soon light came on twice (once when tank nearly empty, then once more ~100 miles later, went off on its own both times).

Checked mileage on the last tank of 87octane and it as 15.8mpg (427m on 27gal) .

Driving habits:

From reading here, I've kept nearly ALL shift points @ or below 2k RPM, & max speed of 70mph (1850rmp) on the interstate. The vast majority of those miles were @ 55, not much stop&go driving either. AC not runnig. I can't really drive it any easier.

I don't know any codes because I don't know how to get them.

Undoubtedly it should be better than 16mpg when being driven that softly, shouldn't it?

Mark_in_Tulsa · January 19, 2006

Nope, sorry.

skills4lou · January 20, 2006

If you don't have a shell, and aren't carrying any cargo that'll fall out: try dropping the tailgate. In my extensive testing that made a difference of up to 5mpg, depending on average speed.

(yes, I'm having fun with smilies tonight!)

Mark_in_Tulsa · January 20, 2006

Not trying to put you down or anything, but it is a very well documented fact that you are more aerodynamic with it up. So therefor you will have better mpg with it up. Many many guys here can confess to that, and show links to prove it. I don't have the time to look for a link.

R Dogg 56 · January 20, 2006

(cues up the Mighty Mouse theme...)

The late great tailgate debate

You're welcome.

Mark_in_Tulsa · January 20, 2006

(cues up the Mighty Mouse theme...)

The late great tailgate debate

You're welcome.

<{POST_SNAPBACK}>

Thanks

skills4lou · January 20, 2006

Mark,

No offense taken. That's what these forums are for. I guess I hadn't considered that different vehicles would have such vastly different results. My results where on a 91 F150 regular cab 8' bed. I'll have to do some experimenting with my new truck.

RT8 · January 20, 2006

Ok, so does anybody have any ideas for THIS truck?

srlbotanical · January 21, 2006

I have the same truck (more or less) as you but a 97. When it was totally stock, I would get about 15 in town and 17 on longer highway trips. I put an intake kit on it and duel exhaust and now I get a whopping 16 mpg in town and 19 on the highway if I'm lucky and I keep my foot out of it.

So, 15.8 is within the ball park...

As for the codes, you need to get them checked. Go to your nearest autozone, or similar auto parts chain. They will usually pull your codes for free. Write the numbers down and let us know what they are...

Steve

RT8 · January 24, 2006

Apparently, when I had to put a new battery in it over the weekend, it reset the codes. Autozone didn't find any. Guess I have to wait until the SES light comes on again and try again.

fmjhp594 · January 24, 2006

Since you might not know the full service history of the truck, you might want to think about doing a simple tune up, oil change, oil filter, air filter, spark plugs, fuel filter. Changing these surely would help out and it only would cost you a little bit. Plus as you're changing things you can see how well the engine is doing, by reading the plugs, looking at the oil, and the filters.

RT8 · January 25, 2006

I don't know ANY of the service history of it prior to the weekend I bought it. It was a trade-in (for an '06 version) at the dealership my father-in-law works for. They changed the oil the day before I drove off with it.

I looked at the air-filter before I bought the truck, it looks nearly new.

I changed both the fuel & transmission filters the first week I had it.

I haven't changed the plugs yet, but there next on the list.

Mr. Smith · January 25, 2006

I've read old topics here until my eyes are hurting but haven't come up with a consensus, so here goes:

'98 K1500 Silverado extra-cab, regular bed, Z71, w/350 & auto w/OD

100k miles

I bought it 3 weeks ago, bone-stock as far as I know (still has single exhaust on it).

Service Engine Soon light came on twice (once when tank nearly empty, then once more ~100 miles later, went off on its own both times).

Checked mileage on the last tank of 87octane and it as 15.8mpg (427m on 27gal) .

Driving habits:

From reading here, I've kept nearly ALL shift points @ or below 2k RPM, & max speed of 70mph (1850rmp) on the interstate. The vast majority of those miles were @ 55, not much stop&go driving either. AC not runnig. I can't really drive it any easier.

I don't know any codes because I don't know how to get them.

Undoubtedly it should be better than 16mpg when being driven that softly, shouldn't it?

<{POST_SNAPBACK}>

Change your fuel filter first off. For some reason on these vortec engines if the filter has any restrictions the mileage drops like a rock. I'm not sure what you expected mileage wise but it is unlikely you are going to do much better than 18 in that ext cab. My 97 now and then squeaks out 19 and it is a reg cab short bed 350.

fmjhp594 · January 26, 2006

I've read old topics here until my eyes are hurting but haven't come up with a consensus, so here goes:

'98 K1500 Silverado extra-cab, regular bed, Z71, w/350 & auto w/OD

100k miles

I bought it 3 weeks ago, bone-stock as far as I know (still has single exhaust on it).

Service Engine Soon light came on twice (once when tank nearly empty, then once more ~100 miles later, went off on its own both times).

Checked mileage on the last tank of 87octane and it as 15.8mpg (427m on 27gal) .

Driving habits:

From reading here, I've kept nearly ALL shift points @ or below 2k RPM, & max speed of 70mph (1850rmp) on the interstate. The vast majority of those miles were @ 55, not much stop&go driving either. AC not runnig. I can't really drive it any easier.

I don't know any codes because I don't know how to get them.

Undoubtedly it should be better than 16mpg when being driven that softly, shouldn't it?

<{POST_SNAPBACK}>

Change your fuel filter first off. For some reason on these vortec engines if the filter has any restrictions the mileage drops like a rock. I'm not sure what you expected mileage wise but it is unlikely you are going to do much better than 18 in that ext cab. My 97 now and then squeaks out 19 and it is a reg cab short bed 350.

<{POST_SNAPBACK}>

I agree with the fuel filter. When I bought mine used, it ran fine, kinda, then it pooped out. they changed the filter and it ran 95% better, but then I got an error code and the fuel pump was going out too. while this was going on for about a week, there were many posts here that stated the problems were with the fuel filter or pump. so my opinion is that these trucks are real finicky with fuel delivery and how it affects performance.