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I used a half can of Seafoam in a full tank of gas for my 2002 Forester. Prior to using the Seafoam, I was getting an average 22.7 mpg. Post treatment, for the past 5, or so, tanks, I've now been averaging about 19.5.

I did get an oil change after using up the tank of gas that received the Seafoam.

What happened, and how might I get my fuel economy back up?


(The last time the spark plugs and wires were replaced was Spring of this year. I haven't noticed anything strange in engine performance or sound, and there have been no CELs. Also, I have not noticed any new marks / stains on the ground from leaking fluids.)
 

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I suppose it could be a coincidence with a regional switch to winter gas formula. or the car's knock or other sensors altered some setting to adapt to the seafoam.

I'd wait and try a couple more tanks to see if the mileage returns but I doubt seafoam did any permanent damage to anything at just 1/2 can.
 

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I used a half can of Seafoam in a full tank of gas for my 2002 Forester. Prior to using the Seafoam, I was getting an average 22.7 mpg. Post treatment, for the past 5, or so, tanks, I've now been averaging about 19.5.

I did get an oil change after using up the tank of gas that received the Seafoam.

What happened, and how might I get my fuel economy back up?


(The last time the spark plugs and wires were replaced was Spring of this year. I haven't noticed anything strange in engine performance or sound, and there have been no CELs. Also, I have not noticed any new marks / stains on the ground from leaking fluids.)
Not sure if it's starting to get colder out your way since you don't indicate where you're located, but when was the last time you checked your tire pressure? As the air gets colder, tire pressure decreases. In my area right now, the temperature dips below freezing at night and jumps back up to around 50-60 Fahrenheit during the day so I've been checking my tire pressure more often.

Also, maybe you've been running with higher PSI in than recommended in your tires prior to the oil change and the shop guys took out some of the air to match what the door well indicates when you took it in.
 

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The last time the spark plugs and wires were replaced was Spring of this year. I haven't noticed anything strange in engine performance or sound, and there have been no CELs.
i had read on other forums that after seafoam'ing it was recommended to check your spark plugs and replace if they become dirty after the treatment.

I suppose it could be a coincidence with a regional switch to winter gas formula. or the car's knock or other sensors altered some setting to adapt to the seafoam.

I'd wait and try a couple more tanks to see if the mileage returns but I doubt seafoam did any permanent damage to anything at just 1/2 can.
i agree with 1LT. run a few more tanks and see what happens... also, you could disconnect your battery for a few minutes and after reconnecting have your ECU relearn everything. i had an '05 forester x and experienced a loss of MPGs after swapping in a new battery. i drove it like i stole it for a few miles and everything was fine... of course, that's the shortened story :)

Not sure if it's starting to get colder out your way since you don't indicate where you're located, but when was the last time you checked your tire pressure? As the air gets colder, tire pressure decreases. In my area right now, the temperature dips below freezing at night and jumps back up to around 50-60 Fahrenheit during the day so I've been checking my tire pressure more often.

Also, maybe you've been running with higher PSI in than recommended in your tires prior to the oil change and the shop guys took out some of the air to match what the door well indicates when you took it in.
yes, check your tire pressure. i believe subarus are sensitive to tire pressure and MPGs.

good luck.

joel
 

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I do need to double check tire pressure, which reminds me that the tires were also rotated along with the last oil change. And, yes, it is cooling down around me--temps have been fluctuating a lot though--I'm in Cincinnati, Ohio.

I'll keep an eye on it and update in a week or two.
 

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I've noticed my mileage drop by several MPGs over the last couple of tanks. I haven't done anything to the car recently, so I would assume that it's due to colder temperatures, and the gas switch. I noticed it last year too, but summer went waaaaay too long....so long, that it also coincided with swapping my AS tires for my snows, so I wasn't sure how much was gas and how much was tire swapping.
 

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Cars I've owned tended to lose 15-20% when the temps dip below about 55F. It is even worse if you have short drives, since most of the extra fuel burn occurs while the engine is at low operating temp.
 

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I suppose it could be a coincidence with a regional switch to winter gas formula. or the car's knock or other sensors altered some setting to adapt to the seafoam.

I'd wait and try a couple more tanks to see if the mileage returns but I doubt seafoam did any permanent damage to anything at just 1/2 can.
Just for information purposes: The ECM on these cars will learn its closed loop fuel trim. Once the computer sees a change in data from its sensors, it starts its learning process until it finds the fuel trim it needs to run and saves that value setting until it sees another change. These learning curves can happen at any time while driving. It starts at every moment you start the engine.

There is some truth in LT's statement though. Mixing good fuel with bad fuel, various alcohol contents or changes in summer/winter blends do tend to take time to work out the mix in the tank. So, run it as close to empty as you feel comfortable and refill the tank with premium unleaded.

Also, change your fuel filter.

The Sea Foam dissolves carbon and varnish build up in the injectors and combustion chamber. You may also want to equalize the treatment by running a bottle through the induction system to clean the intake and valves of the same carbon. Removing the carbon created by the crankcase ventilation system also helps the air move smoother to the cylinders.


There is an underlying issue. I have never seen fuel economy drop from using Sea Foam. I use it in my cars all year. I can't use the VDC for reference any more, but prior to the SC install, I was getting up to 27.5 mpg. I have a Chevy Cavalier that gets 33 mpg and I have logged as much as 45 mpg on long highway drives cross country. (I built the motor in the Chevy, its a 2.2 Saginaw block) You'll most likely find a simple solution.
 

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cardoc, what would be the easiest/quickest way to run SeaFoam through the induction system? I still have the other half of the bottle.
 

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cardoc, what would be the easiest/quickest way to run SeaFoam through the induction system? I still have the other half of the bottle.
There are a few ways to do it.

Parts store sell a setup for just this kind of job.

Or, you can fashion a feed hose using a long piece of vacuum hose. One end in the bottle, reaching to the base, the other attached to the vacuum port for the brake booster with something in between to control the flow into the intake. It needs to go in slow. Too much and it will flood the cylinders. You could use a clamping tool or get a ball valve from the hardware store to insert inline of the vacuum hose. The vacuum from the engine will suck it out of the bottle. It needs to be slow enough that it will mist upon entering the intake. Running the engine at approximately 1200 rpm will help. When your done, reconnect the vacuum hose for the brake booster and drive it around the block to assist in sucking out any residual from the intake and also speed up the vacuum and pressure in the intake and engine to force the loosened particulates out the tailpipe. A couple of high rpms, then off the throttle will increase vacuum from the engine to assist in pulling the loosened material through.

Smoking out the tailpipe is normal when performing this and will stop once all the chemical and carbon are blown out.
 

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I was told 1/3 can tank, 1/3 can oil, 1/3 can in vacuum. After you put it in your vacuum you are suppose to shut your engine off for 5 min and let it sit. Then run out the smoke.
 

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Subaru makes a tool for dispensing top engine cleaner into the intake via a vaccum source. I just ordered one online and its made to fit on the bottle of subaru cleaner. It has a ball valve on it and is all metal except for the tubing that plugs onto the vacuum line. Looks easy to control the flow with this. You could also save the bottle to use seafoam later if you want




 
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