MILEAGE: 3.0=Good, 3.8=Bad ???

[MrCreosote]

My 2000 cargo 3.8 gets around 12 mpg around town. It will get over 20 on a trip but I don't think it can break 24 or 25 mpg.

A lot of people seem to have 2 kinds of Windstars: 17 or better city and around 12 around city.

What I noticed is that usually, the person posting does not say which engine they have so I was thinking could it be that simple?

I know around 1979, GM made some 3.8's that taxi businesses killed to get. These cars got way over 25 mpg around town. First impression was that the gas gauge did not work!

But that was not enough to identify these particular cars. You had to get the 3.8 with the "right colored injectors." I don't remember what color the good ones were but it was that ridiculous. The "other" 3.8's got 12-15 mpg around town just like all other cars.

So what was GM doing?

There was even a road test of a GNX where they had the fifth wheel on the car and they were getting over 40 mpg on the level highway.

To this day, no cars being used as cabs get that legendary " '79 3.8" gas mileage.

Why or Why or Why?

[tomj76]

I have a '96 with the 3.8L engine. Apparently >90% of Windstars from that year are equipped with the 3.8L engine.

Because we used the vehicle for voluenteer activities, I recorded all trips durng the first few years of ownership. Since then we've recorded gas purchases only. In general we tend to fill up at the end of each tank. We drive many interstate highway miles, but we also live in a very conjested area. I'd guess that our mileage is close to 50% highway driving.

About a year ago I decided to enter all my records into a speadsheet and I charted the gas milage over the life of the vehicle. The chart showed a gradual decline of gas mileage down to about 14-16 mpg until the transmission failed about 15 months ago. When the transmission was replaced the gas mileage jumped up to 20-22 mpg again.

[MrCreosote]

TomJ,

Did you notice a difference in the shift points and torque converter behavior after the trans replacement?

In particular, the TC modulates and you see the step from something like 50% lockup to 100% lockup.

Did you notice any difference in the 40mph threshold for OD and TC lockup to occur?

Thanks
Tom

PS
My trans lost the front pump around 80k. Transmission guy lost his shirt on my job because he could not get a rebuild of my transmission to work properly - it kept doing "small" malfunctions a non-car person would never recognize. (It was probably my fault because this other BS trans guy said he could fix it with additives and that resulted in my frying the trans down to a smoldering heap. Probably some burnt oil in a nano-orifice was the problem.)

So he replaced trans with one from a junk yard after giving up on the 3rd rebuild of mine.

Seriously, I am convinced that these newer transmissions have a number of very small orifices that would be difficult to clean if plugged. The real solution would be to use a shop that ultrasonically cleans the case. Now THAT would solve any kind of cleaning concerns. Unfortunately, the only people I know that do that on a regular basis for blocks and cases are NASCAR builders - but I would think it should be catching on with all the promoting of ultrasonics at the various trade shows.)

[tebo77]

A lot of people seem to have 2 kinds of Windstars: 17 or better city and around 12 around city.

I don't know what GM did, but I have noticed a tune-up and proper maintainence make a difference. Also many factors, like point of purchase. There is a station in town with a reputation of having "watered down" gas which is a few cents cheaper. I spend less at the more expensive stations because it increases my mpg by 2-3. My Windstar is the 3.8 and gets 17mpg in town and 21 highway with Mobil fuel, regular not high octane or anything. The cel was/still is on when I bought it a couple months ago, so I've been doing a lot of work to it including plugs, wires, air filter, fuel filter, (these were all in before calculating my mpg for the first time) pcv, fuel injector cleaner (Berryman's Chemtool B-12), more sensors than I can name etc. but for not running right, I can't complain about the gas mileage Can't wait to track it after I get the engine light to go off!

[wiswind]

It makes sense that a slipping transmission will cause a loss of fuel economy.
A remanufactured transmission from a reputable source ($$$) should have been completely cleaned and upgraded to the latest modification level.....versus a repair or "rebuild".
Being very meticulous about changing the transmission fluid and having a auxillary cooler.....making sure that the radiator fans work (always ON when A/C is on) will all go a long way to keeping the transmission working properly.....
Fuel economy also takes a hit at speeds over 60mph due to wind resistance....I have seen figures quoted at up to 15% reduction at 75mph versus 60mph.
Tire inflation is another factor......the sidewall max pressure listed on my tires is 45psi (varies by tire model), I have 40psi in mine.
The biggest thing you can do....other than keeping your vehicle in tip-top shape is to avoid rapid accelleration and high speeds.

[s1120]

I get about 22 out of my 96 with 3.8L. Thats about 75% highway. The key is driving style. If you keep the throttle input low leaving a stop, and try to get over 40 your good. 40 seems to be the OD/lockup point on mine. Also when you do hit the highway, keep your spered down. You will realy start to drop MPG the more you get over 35mph

BTW my best tank was a 24.5MPG. that was on a road trip, loaded heavy.

[tomj76]

I don't think the shift points changed much, but I can't say that I paid close attention to that at the time (before the replacement). However, I did notice an intermitten front end vibration prior to that. I never attributed it to the transmission at the time, but I've since learned that it was probably caused the torque converter clutch. The transmission people called this "chatter". The engine speed will suddenly increase by a few 100 rpms and the steering wheel will vibrate for a second or less, then it returns to normal operation. This generally occurs at highway speed, but it also occurs on primary streets. It has happened when the transmission shifts to O/D, which happens at no less than 30 mph (but at higher speeds during hard acceleration) or while crusing at 65-70 mph. It has also occured when the transmission was operating in drive, such as when climbing a steep grade.

I've had trouble with the replacement transmission in that regard too, in fact the vehicle is at the transmission shop right now as they try to isolate the cause of this. Since the overhaul they've replace the TCC control selenoid and the torque converter (under warrenty). Each repair initially improved the situation, but as time progressed it gradually reappeared.

I once read that MPG are maximum at 40-45 mph, but I think this will vary with vehicle factors such as drag, engine size, vehicle weight, transmission type, and A/C usage as well as the terrain you drive. The national 55 mph speed limit was implemented for reducing fuel use.

[s1120]

I will agree that 45 is probably best for the Windstar. 40 is good to, but sometimes its on the edge of kickdown from OD, and TC unlock.