Has anyone experienced a decline in gas mileage after SOA coolant additive was added to their engine? I recently replaced spark plugs, air filter, fuel filter, on a 2001 OB and have experienced a dramatic (2-3 MPG) loss in fuel efficiency. Please advise.

Dr. Rock,

 

I've had the coolant additive put in my 02 OBW and no change has occurred in my gas mileage. From the list of things that you said were changed on your car, at the same time as the additive was put in the coolant, logic tells me that your problem has got to be one or more from the list. A bad plug? Bad coil? ( My 97 OBW had an ocassional miss firing plug that was traced back to a bad coil, even though the coil tested out fine, but when changed with a new one, the misfire was cured. ) I sure would start there. I can't see how the coolant additive could have any effect on gas mileage.

Possibly the switch-over to winter blend gas?

I think the waiver for epa blends of gasoline are still in effect from Katrina. I would say from that list the LEAST likely culprit is the additive. Could it be the wrong heat range of plugs? What brand plugs were installed. Subarus can be picky with plugs.

 

nipper

NGK plugs from Subaru dealership.

I think I will try the wires and then if there is no improvement look at the plugs. How can you tell a plug is bad? Thanks for all the info. I am relieved that the additive is not the culprit.

Well it will be obvious if you have a fouled plug. Check the gaps, and the heat ranges. Plugs come in three heat rangers, cold, normal and hot. Hot plugs are used if you have fouling issues and drive only around town (think little old lady).

Cold is if you burn up plugs on the highway or heavy load. Normal is well, normal.

 

http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp2.asp?nav=31000&country=US

 

 

nipper

defective spark plug?

loose plug wire?

Random event?

But not coolant additive, that is for sure!

So......When I initially changed my plugs two months ago I noticed one plug was fouled (the tip was covered with oil). All other plugs looked great. At the time I thought changing the plug would rectify this problem, however now I am beginning to think that there might be other isssues. How should I approach getting to the root problem? Any advice wold help.

 

 

Thanks

Oddly enough. I have recently added the additve, and since then, I have noticed a drop. Since then, I have replaced both o2 sensors, and no matter what, I get 23mpg no matter what!!! I don't know what the deal is.

 

Perhaps the mechanic spliced the wrong wires on the o2 sensor??? TIA.

In the last week alone I've seen at least six "strangely, my mileage just dropped" posts on various groups.

 

It's gotta be off-spec fuel ...related to the hurricanes somehow.

In my case I feel that my mileage has slowly been dropping since about mid July. At that time I did my spark plug/fuel filter/air filter work. And also had the additive added at that time. I live in seattle and I am wondering if we even get "hurricane affected" gas. But then again standards were dropped across the country so maybe our gas is refined the same at this time.

 

I took out all plugs today. They were fine. I think I have ruled out the plugs and now will look at the plug wires.

 

d

to the coolant. I got 25mpg before and 25mpg ever since. I have not checked mpg lately but would not be surprised to see a couple mpg drop with the crummy fuel available. I'll check back in a couple of weeks to let you guys know what I'm getting here in CA for mpg now.

no drop with the additive, however i still do hand stands every time i fill the outback...as prior to that i was filling a dodge ram, 100bucks a fill give or take. So needless to say i don't follow my mileage as closely as i could, i just know it costs less than half on the ob.

 

i would think your loss is related to something other than the propaganda additive. The idea of suspect gas due to the hurricanes etc is an interesting idea.

So......When I initially changed my plugs two months ago I noticed one plug was fouled (the tip was covered with oil). All other plugs looked great. At the time I thought changing the plug would rectify this problem, however now I am beginning to think that there might be other isssues. How should I approach getting to the root problem? Any advice wold help.

 

 

Thanks

 

 

You have forgotten some information. Particularily, how many miles on the vehicle? Weather you have done a fulll service to it, or just the items that you mentioned. You might also might want to look at the following post concerning the oil on the plug wire.

 

http://www.ultimatesubaru.org/forum/showthread.php?t=24449&page=1&pp=10

 

I think a fouled wire could cause a decrease in mileage more than any additive. Never had a customer complain of that.

So......When I initially changed my plugs two months ago I noticed one plug was fouled (the tip was covered with oil). All other plugs looked great. At the time I thought changing the plug would rectify this problem, however now I am beginning to think that there might be other isssues. How should I approach getting to the root problem? Any advice wold help.

 

 

Thanks

 

if the tip of your spark plug was oil covered, it could be a sign of a bad valve cover gasket... I know for sure that Oil on the plug wire is a sign of it, thinking that oil on the tip could/would/should be a sig too...

 

as far as bad mileage... Had to gas up quite early this week too. Think I only got 240 miles before the light came on... Never had that before.. The last gas up was a SAMS CLUB... I'd have to say either cheap gas (not from SAMS) or "hurricane" blended gas...

You have forgotten some information. Particularily, how many miles on the vehicle? Weather you have done a fulll service to it, or just the items that you mentioned. You might also might want to look at the following post concerning the oil on the plug wire.

 

http://www.ultimatesubaru.org/forum/showthread.php?t=24449&page=1&pp=10

 

I think a fouled wire could cause a decrease in mileage more than any additive. Never had a customer complain of that.

 

A fouled plug on a 4cyl engine can greatly decrease the gas mileage and performance, as opposed to fouled plug on 6, 8, or bigger engine.

 

nipper

I just flipped 80K on the vehicle. No it has not been in for its tune as I wanted to save some money and have been doing most of the work myself except for the belts. Those I had replaced a recently by a shop.

 

When I was taking the plugs out yesterday I did notice some oil on the wires, but none on the plugs themselves. And I too am consistenly getting about 230-240 miles per tank (city driving). I always got around 300 before the light went on before. Perhaps some of this can be attributed to gas but I definitely think there are other things going on.

Ok lets break this down

 

The hurrricanes, there is still a EPA waiver in effect so there are no more regional gas blends untill refineries are back at 100% or 90 days, i forget which.

 

If you have changed plugs lately, which brand did you install?

 

Wet wires, check to make sure your valve covers are tight, as they do losen up every so often.

 

Has the weather changed? If it has, check your tire pressures.

 

How are your brakes? A sticky caliper can cause a reduction of gas mileage.

 

Have you changed your driving route to and from work lately?

 

Heavy use of ac will drop gas mileage (this is true for using the defroster a lot).

 

How is your wheel alignment?

 

Has somone else been driving your car alot more then in the past?

 

And there is always the planets are in alignnment causing more intersteller gravitaional drag on subarus, since the car is named after a star cluster...

 

 

hehe

 

nipper

The hurrricanes, there is still a EPA waiver in effect so there are no more regional gas blends untill refineries are back at 100% or 90 days, i forget which.

re: Crappy Gas/ Lotsa people suddenly experiencing reduced mileage.

 

"To ease gasoline shortfalls, the Bush administration relaxed rules on emissions and GASOLINE QUALITY this week."

 

http://www.chron.com/cs/CDA/rssstory.mpl/business/energy/3337948