Minivan Poor Fuel Economy

gasoline
fuel-economy

#1

I have just recently started measuring my gas mileage, and was very surprised to see that I am only getting about 10 MPG in city driving. I have a 2000 Oldsmobile Silhouette Minivan, and it’s supposed to have a better MPG than what I am getting. What can I do to help this?


#2

Howdy, have you checked the air filter a dirty one will sure reduce the mpg.


#3

Have you kept up with your 30/60/90K services? Changing filters, PCV, and plugs when the manufacturer says is important for good operation and good mileage.


#4

i actually don’t think youare getting THAT low a mileage number. i think the specs were around 19 city, and 26 highway. so you are low, but not that much. upon redirection (aka roadrunner) a 50% drop is too much.

do the recommended maintenance as suggested. your owners manual is your FRIEND. read it.

if you don’t have one yet, find a good local mechanic. references, and personal recommendations are best. stay away from chain lube, tire shops too (unless just for tires) for repairs. find a regular shop, with two or three mechanics.


#5

It is quite likely your Olds is in proper mechanical condition and is running normally. There is no reason to believe this is not so. Your estimated 10 mpg is the result of your normal driving habits. This is not unusual. Many city dwellers can do no better. If this is so, then no amount of repairs or maintenance will increase your fuel economy. Maintain your vehicle anyway, but don’t expect to see an improvement in the mpg department.


#6

The biggest improvement you can do is drive more conservatively. No jack rabbit starts. Keep the speeds down. Don’t go racing up to a stop light then slam on your brakes.


#7

All good posts above except for one moot correction: the 2000 Olds Silhouette 3.4L V6 manuf. estimated mileage is 18-19 city and 24-26 Hwy.

A multitude of things cause different mpg.

I have the same van with 87k miles on it and get a combination of stop’n’go and hwy mileage of 23 mpg.

You don’t say what the mileage is you have on the van or how you calculated the mpg.

If after using at least three tankfulls of fuel and have divided the mileage (at each fill-up) by the amount of fuel used to get a proper reading, and 10 mpg IS the really real estimate, I would suggest you have a compression test done.

Does the engine seem a bit ‘weaker’ than normal?

Do the usual preventive maintenance such as replacing properly gapped OEM plugs (check your owners manual), (the back three are brutal without rolling the engine forward).

Replace plug wires (if arcing is occurring. Check when dark out) with OEM wires.
I tend to stick with whatever the engineers decided was best to make my vehicles go the way they should.

Replace the fuel filter (In-line ahead of the tank, passenger side).

Hopefully the fuel pump isn’t starting to die as it is in the tank.

Do a fuel pressure test at the fuel rail.

Others may differ.


#8

my wife has a similar van (2001 Pontiac Montana minivan)…we experienced the same problem and were current with all maintenance issues… i did discover that the engine was never really getting hot enough (the temp needle was below the bottom of the guage) for the system to go into “closed loop”. make sure the engine is getting hot enough. if it is not, find out why. we had the thermostadt was switched out and the mileage improved dramatically and is now “normal”!


#9

I appreciate the detailed assistance. I calculated the mileage by resetting the trip odometer after fill up, and then dividing the gallons of the next fill up by the number of miles on the odometer. I did this 3 times already, and the results were consistent. I am referring to heavy city driving, where one doesn’t go 2 minutes without stopping. New York City - get the picture?
The engine does seem a bit weak, when idling - the engine starts making rumbling noises and will stall after approximately 4-5 minutes, unless it has warmed up significantly. It takes a long time to achieve full system performance on a very cold day, there will be a delayed response from the engine when accelerating after a red light stop. Can these issues be corrected with a proper tune up?


#10

Ok, if you’re doing everything right you’ve included changing the air filter as well.

The driving conditions you describe I can only imagine. I stay well away from large cities.

At any rate, a ‘tune up’ today doesn’t entail half the things we did 40 years ago.

What I’ve already touched upon covers most (but not all) components.

FWIW, your driving conditions are what the manufacturers call ‘severe’.

This means servicing must be done more frequently (this includes replacing tranny fluid and filters at 25-30k miles instead of 50k.

The engine stalling may be due to a faulty IAC (Idle Air Control) valve and or a dirty throttle body.

“A delayed response”? As in ‘hesitating’? If so: You may have a faulty ignition system; dirty fuel injectors; low fuel pressure or perhaps an emissions glitch.

Do you know which thermostat is installed? In this engine it should be a 195 deg. 'stat.

You might want to take the van out on the highway for a hours’ run once a week or two.


#11

(The temp needle was below the bottom of the gauge)!

You sure the t-stat wasn’t stuck in the open position and not the wrong one? Just curious.

What was the old t-stat and what is the new one?


#12

You said it backwards. You meant to divide the miles by the gallons. You did it right, and that’s what counts. If your city trips are all less than ten miles, your car will show lousy city mileage. If the trips are all the mile and a half variety, the ten MPG is good.


#13

the t-stat was stuck open…the needle failed to climb to the bottom of the gauge (160 i think)… my mileage was “lousy”… new t-stat and coolant temperature sensor and all is right…


#14

If your driving so little miles the # makes sense. Also if you driving few city miles anyway even at 10MPG you are still not spending much on fuel since your miles traveled is not high.