New Clutch = 19 MPG? WTF?

[IntoTheVoid]

What is the logical explanation for this? Has this happen to anyone else?

So here is the story:

When I first got my 4runner it had Pirelli's 275/16 and got 20-21 out on the highway. I had them on for about 4 years and the mpg was always the same.
Then went to Cooper Discover STT 285/16 and my mileage dropped to 14-15 mpg out on the highway over night.

Last week I replaced the clutch due to a bad pilot bearing. It was a Toyota clutch kit and now I am getting about 19 mpg or better out on the open road.

I just took a trip to Seattle this weekend. Filled up and took off Friday afternoon. On the way up there I noticed my gas gauge was pretty full after about 75 miles. Drove a little more and I really thought my gas gauge was stuck! Pulled off I-5 at a rest area and my gauge moved a little so then I knew the gauge was working.

Got to Federal Way and spent the night. The next day we drove to Lynnwood to pickup some oxyacetylene tanks and take them up to Woodenville. Then back to Maple valley to Enumclaw then down to Auburn.

Got to Auburn and had a 1/4 tank. Filled up with 270 miles on the trip meter and put in 14.3 US gallons. I figured the mileage right there on the spot. 18.8 mpg...I pissed myself.

I really think it is going to closer to 20+ mpg because on the way up I got stuck in stop and go traffic for 45 minutes from Ft Lewis to Fife where I bailed off I-5 because of all the traffic.

I did nothing to my rig other then the clutch but I did have the battery disconnected for three day during the clutch replacement.

The mileage went up over night with the new clutch just as it went down over night with the bigger tires. But now I have bigger tires, new clutch, and 20 mpg! :driving:

 

[Full_Throttle]

Are you compensating for actual miles driven vs what the odometer says? With bigger tires you travel farther than what the odometer says. For every 250 miles I think I have to add close to 30 miles to what my odometer says, so when mine says 250 I have really driven around 280ish.

 

[newmexrunner]

Are you compensating for actual miles driven vs what the odometer says? With bigger tires you travel farther than what the odometer says. For every 250 miles I think I have to add close to 30 miles to what my odometer says, so when mine says 250 I have really driven around 280ish.

So with that logic he would be getting better gas mileage than what he actually thinks he's getting correct?

 

[Full_Throttle]

So with that logic he would be getting better gas mileage than what he actually thinks he's getting correct?

assuming he isn't already correcting, yes.

 

[spectre6000]

It sounds like your old clutch was probably a bit glazed. Due to riding the clutch it heated up and got really smooth, thus reducing the available friction. When you upped the tires you upped the amount of torque required to move the car, and the clutch was unable to keep up as well as it had with the smaller tires. By replacing the clutch, it has purchase on the flywheel and pressure plate and you have torque again. If you were to go back to your smaller tires, you'd see an even greater increase in fuel economy.

 

[IntoTheVoid]

It sounds like your old clutch was probably a bit glazed. Due to riding the clutch it heated up and got really smooth, thus reducing the available friction. When you upped the tires you upped the amount of torque required to move the car, and the clutch was unable to keep up as well as it had with the smaller tires. By replacing the clutch, it has purchase on the flywheel and pressure plate and you have torque again. If you were to go back to your smaller tires, you'd see an even greater increase in fuel economy.

Now that sounds like a logical explanation.

I have had the 285's on since last December and driven up that way at least 4 time since the 285's. I know how many miles it is to my sister place because I have driven it about 100+ times since 1993 in three different rigs. Even with the bigger tires my trip meter still said the correct mileage before and after the 285's so I know there is not a big difference in the tire size, it is very minimal.

 

[agloukhoff]

Did you look at the old clutch? If it was at the end of its life it was probably slipping a little which may explain some of the difference but it'd have to be slipping pretty regularly and you'd probably smell it...

 

[ctruss53]

You are complaining about 19MPG?

I just bought my 2000 Limited and I was half expecting 20MPG. On my first tank through I averaged 18MPG.

So if thats low I'm thinking I'll need to do a tune up, maybe replace the O2 sensors, and also look into a high flow intake.

I was going to look at intakes and exhausts to improve mileage anyways.

 

[IntoTheVoid]

Did you look at the old clutch? If it was at the end of its life it was probably slipping a little which may explain some of the difference but it'd have to be slipping pretty regularly and you'd probably smell it...

Yes it still had some life in it maybe..maybe 30k?
Here are some pictures of the old.
http://www.toyota-4runner.org/3rd-gen-t4rs/119873-168-000-time-new-clutch-woohoo.html

Yep, no smell at all and it slipping was the farthest thing from my mind. Maybe a little but not that much.

 

[IntoTheVoid]

You are complaining about 19MPG?

No not at all.
It's a good WTF happened to make my MPG to improve over night?

 

[983RDGEN]

A little of subject but what do you thinkl about the Cooper tires so far?

 

[spectre6000]

It's a little hard to tell from the photos, but the clutch looks OK. The pressure plate has some pretty obvious hot spots though... Did you have it (and maybe the flywheel) turned while it was out?

 

[IntoTheVoid]

A little of subject but what do you thinkl about the Cooper tires so far?

Even better now since my mileage went back up!

The STT's are very nice. Quite, great in the rain, mud, snow. Going to try them out in the desert soon.

I was going to put Dean Wildcat EXT on but they stopped making them. I really liked that tire.

 

[IntoTheVoid]

It's a little hard to tell from the photos, but the clutch looks OK. The pressure plate has some pretty obvious hot spots though... Did you have it (and maybe the flywheel) turned while it was out?

Yes the flywheel was turned. Did not make any sense to me not to turn it if I was going to put a whole new clutch kit in.

If you look at the picture with the pilot bearing, it is sitting on the clutch. You can see how deep the rivets are from the surface. It was getting close but I still had some clutch.