Is it possible?

[otis24]

I have a 1991 Pontiac Sunbird LE (2.0). Neighbor purchased it when it had about 8k miles and it has only been driving in town. It has averaged about 4k miles per year over the past 19 years. I am averaging about 1k miles per month, so it sees a lot more driving. It currently has about 83500 miles.

When I purchased it a couple of months ago, the air filter was very clogged and dirty. I changed air filter, pvc valve, thermostat (which had been stuck open for who knows how long), oil filter etc... I added Auto-Rx and am about 1500 miles into a cleaning cycle. I drive six miles one way to work and average about 25 miles per day by the time I come home for lunch, run errands, etc.. I was averaging about 22 MPG for starters. Now, I am getting 25-27 MPG. Is it possible that the Auto-Rx is is cleaning the engine up and increasing fuel economy?

 

[spasm3]

I think its more that the engine is up to temperature and that affects the computer. You are probably not running as rich as when you were running cold all the time.

 

[dwendt44]

Rregaine fuel cleaner for a couple of fill ups might help a bit too.

What does the oil look like at oil change?

 

[otis24]

Don't know what the oil looks like. I changed it when I first got it and added a half quart of Marvel Myster Oil. Changed again in 500 miles (very black) and added Auto-Rx. I'm only 1500 miles into the cleaning phase. Won't know for a while yet what the oil looks like, but it doesn't appear extremely dark on the dip stick.

 

[IndyIan]

Replacing the stuck thermostat will have made the most difference, nothing you put into the oilpan will help increase mileage significantly.

 

[asamek]

I would think the new air filter would make a difference as well.

 

[javacontour]

Bingo! Stuck thermostat was likely the culprit. Fixing that allows the engine to run at operating temperature and it's no longer running rich.

 

[otis24]

Just to clarify, I was getting about 22 MPG after changing air filter and thermostat, pvc etc..
The MPG has seemed to creep upwards since adding the Auto-Rx. Perhaps it is a combination of things. I was disappointed at getting only 22 MPG. Didn't seem like it was going to save me much over my 98 Jimmy.
I topped off the tank last night after adding a bottle of Regane. Fuel economy was about 27 MPG. I will double check that figure when I get to about 1/4 tank.
At that rate, I am getting more than double the MPG for back and forth to work than with my Jimmy.

 

[javacontour]

If the car was driven with the thermostat in that state for a long time, it could take a while before the fuel trims adjusted to reflect the new state of the engine.

It's probably a combination of things AND time as the car adjusts to being driven by a new driver.

And yes it does. The computer "learns" so I believe that's part of it.

How much carbon build up and everything else was in there from such short term driving?

Since you've changed more than one variable, it's hard to say which one has the most impact.

 

[mechtech2]

Mainly thermostat.

A dirty air filter in a fuel injected car does not richen things up like a carbureted engine.