Gas milage is crashing at an alarming rate...

[kenratboy]

First, Bruce FTW -->

Car is a 1997 with a V6 and 5-speed.

When I bought my car about 5 years ago (75k miles), I consistently got 27 MPG in combined driving. However, in the last year, and recently, my mileage is starting to tank. Filled up today after driving the same sort of routes that gave me 27 MPG, and I got just under 22 MPG (a drop of around 23%). Also, I took a road trip a few years ago and got a (shocking) 33 MPG - same trip and I was around 27-28 MPG.

What the hell is happening!?

I'll give you something to work with:

-It has been very cold (but not sure that is it).
-I just got the clutch replaced (that did not change anything)
-I switched from some decent-performance Falken's to some decent-performance Bridgestone G009's about a year ago (could this be a cause)? Tire pressure is checked regularly.
-Spark plugs were replaced around 90,000 miles, which was probably ~3 years ago.
-To my knowledge, I don't think anything like PCV or other sensors have been replaced.
-Air filter is new, and I replace it more than needed.
-I have not put on 500lbs. since I bought the car.
-No other modifications or adjustments.
-Driving style has not changed much.
-I have not noticed a chance in performance or how the engine operates (everything feels OK).

What should I try first? Are there some simple things I can do myself like checking vacuum lines, changing/checking/cleaning sensors, etc.?

It is not a huge deal now, but if there is something I can do that takes an hour or costs $20 to improve things, I want to do it sooner rather than later.

Thanks!!!

[96paseo]

Check your ECT sensor. This can be done with an ohm meter. If its malfunctioning, the ECM could deliver too much fuel at normal operating temperature. Has your EGR been cleaned? You could also run some seafoam through the fuel system and vacuum lines.

[JohnHarlin]

Sometimes it is best to start with the obvious, eliminate that possibility and go on.

During a tuneup I had my air filter changed, my 02 censor changed, everything passed their computer sensors and I still get rotten mileage. Now I'm going to get an old change and use plane old fuel injector cleaner and see what happens. Sometimes after I haven't driven for 4 or 5 days a lot of dirt comes out of the exhaust. I don't know if that means anything or not.

Anyway, it wouldn't hurt to try fuel injector cleaner. The cost would probably be something like $7.

[toyomoho]

O2 sensor, changes in gasoline mix (adding more alcohol), softer tires can decrease MPG.

Cold?

[Mike Gerber]

To add to what 96paseo and toyomoho have suggested, a slow opening thermostat or one that is stuck in the open position can also reduce fuel economy. Does the car seem to warm up as fast as it used to?

Mike

[kenratboy]

Originally Posted by 96paseo

Check your ECT sensor. This can be done with an ohm meter. If its malfunctioning, the ECM could deliver too much fuel at normal operating temperature. Has your EGR been cleaned? You could also run some seafoam through the fuel system and vacuum lines.

I'll take a look, is it somewhat easy to do?

I would love some (semi) easy projects to play with. I would be thrilled if an hour or two and a few bucks could fix things.

Even if money was not the issue (burning more fuel), this means I have to fill up more often!

[kenratboy]

Originally Posted by JohnHarlin

Sometimes it is best to start with the obvious, eliminate that possibility and go on.

During a tuneup I had my air filter changed, my 02 censor changed, everything passed their computer sensors and I still get rotten mileage. Now I'm going to get an old change and use plane old fuel injector cleaner and see what happens. Sometimes after I haven't driven for 4 or 5 days a lot of dirt comes out of the exhaust. I don't know if that means anything or not.

Anyway, it wouldn't hurt to try fuel injector cleaner. The cost would probably be something like $7.

I actually did it maybe 6 months ago, but not convinced its ever been used before that, so maybe it needs some more!

What brand/type should I use?

[kenratboy]

Originally Posted by toyomoho

O2 sensor, changes in gasoline mix (adding more alcohol), softer tires can decrease MPG.

Cold?

Cold = it has been a very chilly winter compared to the average. My book says I have 3, O2 sensors it looks like, and it appears they are all VERY expensive.

[kenratboy]

Originally Posted by Mike Gerber

To add to what 96paseo and toyomoho have suggested, a slow opening thermostat or one that is stuck in the open position can also reduce fuel economy. Does the car seem to warm up as fast as it used to?

Mike

I think it warms up fine. Not sure how hard the job is, but if its a cheap part and not too hard to do, I might just do it for the heck of it.

[Hajoca]

How cold is cold?? are gas stations now supplying you winter gas? (More ethanol)

[kenratboy]

Well, lots of night well below freezing (0-25 degrees F common at night), but still seems extreme that things would be this bad.

Even when I was in the Bay Area for 3 days (very warm), still had the issue.

[rty]

If my 97 V6 got 22 mpg I'd be happy. My last tank was 17 mpg. In the summer I can get 22 mpg so the cold does produce a pretty significant drop.

[cruisn76]

Originally Posted by kenratboy

I actually did it maybe 6 months ago, but not convinced its ever been used before that, so maybe it needs some more!

What brand/type should I use?

Go to Walmart/Costco and get Chevron Techron Fuel Injector cleaner.

Google this and you will find many forums talking about it. I say about 60-70% good comments on Chevron Techron fuel injector cleaner

Here is a picture of what it looks like:
http://www.amazon.com/Chevron-TECHRO...=pd_sbs_auto_2

I have used it for about a year now (about 4-5 20oz bottles) and I consistently get good mileage. My only problem is a stuck thermostat during the cold winters. Which is affecting my gas mileage from 600km a tank to about 550km a tank

[BMR]

Perhaps your brakes are dragging? See if any of the wheels are hotter than normal after you've driven a while. If a brake is dragging, it'll be uncomfortably hot to touch.

[96paseo]

Originally Posted by kenratboy

I'll take a look, is it somewhat easy to do?

I would love some (semi) easy projects to play with. I would be thrilled if an hour or two and a few bucks could fix things.

Even if money was not the issue (burning more fuel), this means I have to fill up more often!

Its not that hard. You need a multimeter that can measure ohms. You also need to check it twice. Once in the morning so the engine is completely cold. Second, after you've driven it for about 10-15 minutes to get it up to full temperature. The sensor is the green colored connector on your coolant outlet housing. Does your temp gauge get up to 1/2?