With 100,000 miles on my Toyota, i've noticed a decrease in gas mileage over the last few months. I have changed the plugs, and used fuel injector cleaner regularly. All required maintanence has been done. Valve adjustments are not required on this car. This is why I became concerned with sludge and engine flushes. After reading up on it, I really don't think it is sludge and I don't need to use an engine flush. What else could it be? 100k miles is allot so maybe this is just part of the aging process. It is not a significant decrease so it is not that big of a problem.
Decrease in MPG
- Thread starter buster
- Start date
- Status
how big of a difference?
winter gas?
winter gas?
I have noticed about a 2 MPG drop since the temps have gotten colder.
I have the same problem. My caddy has the dig. average readout.
Im pretty sure its normal, since when your start your car, it runs pretty rich to warm the car up i believe....
Im pretty sure its normal, since when your start your car, it runs pretty rich to warm the car up i believe....
my fuel economy is much worse now too. In the warm weather, I usually get 400miles to a tank. Now I'm not exaggerating when I say I struggle to get 250-300 miles to a tank. The saturn is very finicky with gas; this may be a contributing factor.
--Matt
--Matt
I noticed a 2-3 mpg decrease over a couple of months. I thought it was due to the much stickier tires I installed, but decided to check the PCV valve because the check is trivial (squeeze the hose between the valve and intake manifold, and you should hear a click).
The valve was bad and I replaced it. $15 at the dealer and 5 minutes. The first tank gave a fuel economy near the top of recorded history (third best tank in the last 19,000 miles), so I think I found the culprit. A long driving vacation is planned for this month, so that should confirm that the problem's solved, and if so I should save enough gas money to pay for the valve!
The valve was bad and I replaced it. $15 at the dealer and 5 minutes. The first tank gave a fuel economy near the top of recorded history (third best tank in the last 19,000 miles), so I think I found the culprit. A long driving vacation is planned for this month, so that should confirm that the problem's solved, and if so I should save enough gas money to pay for the valve!
Patman
Staff member
I'm going to try this in my wife's 2000 Civic! Her gas mileage has steadily declined since last year. This time last year she was getting 25MPG, now she gets 20.5 to 22 MPG! She drives the same way as before, with less idling than last year too.
The most common cause of gradually decreasing fuel mileage is an aging O2 sensor. A bad O2 sensor can cost you at least 5mpg without triggering a check engine light. Also remember that as mentioned cars run way richer on startup when its cold. Also most states require a switch to different fuel formulations during winter (more alcohol I think) which can hurt power and mileage too.
I've been inspired to make a plot showing my decrease in fuel economy:
(The blue line is exponentially smoothed to show trends.) The fuel economy seemed to drop off around 122,000 miles. The last two points are since I replaces the PCV valve. I think keeping careful fuel records pays off when finding small trends like this, especially since my car is due for a smogging in a couple of months. (Aside from the big spikes that represent long trips, my driving patterns are consistent, which also helps.)
Patman, on my Civic engine, the PCV valve is under the fuel rail to the right, as you're standing in front of the car. It's connected by a hose to the intake manifold. If you clamp the hose strongly with the engine idling, you should hear a click as the valve goes from closed to open. In my case, the valve seemed to be stuck open, because the idle changes when I clamped the hose. (Normally the valve is open at low manifold vacuum and closed at high vacuum, e.g. idle.)
To replace the valve, you just pull it straight up, out of its rubber grommet and detach the hose. Installation, as the manuals say, is the reverse of removal. I've read on honda-tech.com that some aftermarket valves don't seat deep enough into the grommet and can leak oil, which is why I went to the dealer.
The ubiquitous Mista Bone has a picture of where the PCV valve is relative to the intake runners (in a D-series engine):
http://home.cinci.rr.com/mistab0ne/Pics2/PCV.JPG
[ January 03, 2003, 02:03 PM: Message edited by: BOBISTHEOILGUY ]
(The blue line is exponentially smoothed to show trends.) The fuel economy seemed to drop off around 122,000 miles. The last two points are since I replaces the PCV valve. I think keeping careful fuel records pays off when finding small trends like this, especially since my car is due for a smogging in a couple of months. (Aside from the big spikes that represent long trips, my driving patterns are consistent, which also helps.)
Patman, on my Civic engine, the PCV valve is under the fuel rail to the right, as you're standing in front of the car. It's connected by a hose to the intake manifold. If you clamp the hose strongly with the engine idling, you should hear a click as the valve goes from closed to open. In my case, the valve seemed to be stuck open, because the idle changes when I clamped the hose. (Normally the valve is open at low manifold vacuum and closed at high vacuum, e.g. idle.)
To replace the valve, you just pull it straight up, out of its rubber grommet and detach the hose. Installation, as the manuals say, is the reverse of removal. I've read on honda-tech.com that some aftermarket valves don't seat deep enough into the grommet and can leak oil, which is why I went to the dealer.
The ubiquitous Mista Bone has a picture of where the PCV valve is relative to the intake runners (in a D-series engine):
http://home.cinci.rr.com/mistab0ne/Pics2/PCV.JPG
[ January 03, 2003, 02:03 PM: Message edited by: BOBISTHEOILGUY ]
While you're under the hood, you might also pull a spark plug or two. If carbon-fouled, this could indicate a clogged catalytic converter...
Patman
Staff member
I'm not even sure if mine has one! I bought a PCV valve from the store but the book listed it for a 96-99 Civic. Mine is a 2000 but I thought the 99s and 00s were the same. After looking for 5min under the hood I can't find any PCV valve at all under there.
- Status
Similar threads
- Locked
