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Old 09-21-2017, 04:45 PM   #1 (permalink)
FastFebur
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Join Date: Aug 2017
Location: Sacramento, California
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Unexplained 100mi/tank drop! '03 civic HX

Hello everyone!
I've joined this site in hopes of figuring out what has happened to the
100-150miles i'm loosing per tank of gas. I've owned my 2003 Civic HX (5speed)
since 2007. It had 60k miles when I bought it.
I've always gotten just shy of 500 (sometimes 10+) miles per tank of gas which would always equate to 40-44mpg depending on my driving style. She now has 250k+ miles. I've never had any issue with her but since about 210k I've noticed a steady decline in mpg. Averaging 34-36mpg all highway.

Basic maintenance has always been performed by myself aside from last timing belt + water pump @ 200k which was done by Honda.
I have no CEL, oil leaks, smoke or anything abnormal that'd indicate an issue to me. No oil is burned (cx every 10k) nor is the coolant ever low. I keep my tires (fairly new) at around 40psi. I first thought that I'd maybe have a fuel leak so I kept it in my garage for a few days several times with varying levels of fuel in the tank and I wasn't able to sniff anything out. Last smog (California) passed.
Plugs were done at about 220k
Air Filter @ 240k
I conducted a cylinder pressure test not too long ago which all came up within spec.
She rolls freely when in neutral so there's no indication that theres something holding it back.

Im starting to commute 180 miles/day 2-3 times a week now and a drop in mpg like I'm experiencing is a determining factor of getting gas in a safe place (Sacramento) or a bad place (Oakland).

What should I turn to next? Maybe a cylinder leak down test??

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Last edited by FastFebur; 09-21-2017 at 04:50 PM.. Reason: pic
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