bad mpg after head gasket repair. any ideas?

[mercuryrising17]

So about a month ago I got my engine back in after doing a timing belt and head gasket replacement. It was my first time ever attempting something so big. The car runs good now ( minus a atf leak) but ever since I got it running again I get really bad gas mileage. I used to get about 300 miles a tank and now get only 240 or 250 a tank. Any ideas on why this might be. should i replace the plugs and wires? Or is there something else I could have done wrong? It just seems wired that the mielage went down after the removal. The plugs are a little old but it just doesn't make sense that they would make a big difference after removing them. Any ideas would help.

[Olnick]

First of all, what model/engine are you talking about? Mileage? History?

 

Basic tune-up always helps an engine run better and more efficiently. New plugs (NGKs) and plug wires (Subaru OEM), new air & fuel filters, new PCV valve. Might even need new O2 sensor and knock sensor.

 

Good luck.

[1 Lucky Texan]

you say it's running well, but I can't not mention the possibility of getting the TB off by a tooth. You might pull the covers to double check.

[bheinen74]

Yeah definitely NEED to take the front covers and pulley off, and check the center cog make sure it is on the marks.

 

I hope you used NGK plugs, and OEM plug wires, etc.

[Mugs]

I used to get about 300 miles a tank and now get only 240 or 250 a tank.

 

The only time I ever get 300 to a tank is when I am on a road trip...in town its about 220-240

 

96 Lego Wagon, auto, EJ22.

 

So what your getting is pretty good....

 

Plus it is now winter...which means more Ethanol in the fuel...equals less MPG.

[Fairtax4me]

How much is a tank? Gallons not needles.

If you're going by what the gauge says, they are notoriously inaccurate, and a car sitting for a long period of time will have extra varnish build up on the sender unit, which will make it that much less accurate.

 

Mechanically, the timing could be off, the front oxygen sensor could have got fouled up, fuel injectors could be varnished and need to be cleaned. Check the timing and try a good fuel system cleaner first, lots of people here recommend Techron because it also helps clean the fuel senders.

[mercuryrising17]

Thanks for all the input I apologize for a lack on info I'm on the road and using my phone to post. It is a 2002 legacy gt with the 2.5 in it. I am only getting 250 miles tops on just under 14 gallons of fuel, I never go of the gushed always by the odometor. I tried fuel cleaner with no help and I have my check engine light on which I believe is because of my 02 sensor. I think it has gone out due to my transmision fluid leaking on the exaust pipe. Would a bad 02 sensor make me get that much worse mpg though? I want to try the easy things first before I mess with the filming again just because I am new to doing this. I was a little concerned about the timing when I put the belt on just because I wasnt sure if the belt move to far back when I pulled the pin on the tensioner. it looked good I just was so nervous I second guessed myself. The car rodent run " rough" so I just assume the filming was correct. Would it run all right if it was one tooth off though?

Thanks again guys this board is an amazing resource of knowledge from amazing Subaru lovers!

[1 Lucky Texan]

Thanks for all the input I apologize for a lack on info I'm on the road and using my phone to post. It is a 2002 legacy gt with the 2.5 in it. I am only getting 250 miles tops on just under 14 gallons of fuel, I never go of the gushed always by the odometor. I tried fuel cleaner with no help and I have my check engine light on which I believe is because of my 02 sensor. I think it has gone out due to my transmision fluid leaking on the exaust pipe. Would a bad 02 sensor make me get that much worse mpg though? I want to try the easy things first before I mess with the filming again just because I am new to doing this. I was a little concerned about the timing when I put the belt on just because I wasnt sure if the belt move to far back when I pulled the pin on the tensioner. it looked good I just was so nervous I second guessed myself. The car rodent run " rough" so I just assume the filming was correct. Would it run all right if it was one tooth off though?

Thanks again guys this board is an amazing resource of knowledge from amazing Subaru lovers!

 

 

Get the code read. A bad/lazy O2 or maf/map or other emissions sensor could easily cause poor gas mileage. Could also lead to catalytic conv. damage,etc.