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Drop in gas mileage - possible causes?; Sudden drop in gas mileage - suggestions to fix?
Topic Started: Jul 28 2012, 06:48 PM (1,109 Views)
JDs96Metro
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Howdy all,

Been awhile since I've been on here. My Metro has been running great the last few months but somethings up. :hmm

My last 4 tanks of fuel, my gas mileage has been: 42, (all city no hwy driving), 44 (mix of city/hwy), 47 mpg (mostly highway, but going 60 - 65), and 51 (all highway, average speed 55). All of these fill ups were E10.

Before I filled my current tank - I checked the oil. It was low so I put in a pint (not a quart) of Marvel Mystery Oil and added a quart of oil (5-30W like normal). Upon further inspection, I noticed my valve cover gasket was leaking in the corner. I'm guessing the contributed to the low oil level. My whole engine is pretty dirty - covered in oil so I'm assuming other gaskets may be leaking too. (Separate topic: I plan to clean the motor soon so I can see better and fix the gaskets).

I've driven about 400 miles with the Marvel Mystery Oil in it.

For this current tank - I've got about a 1/4 tank left but only went 263 miles. I was driving mellow, average about 55 all hwy on a route that normally takes less than half a tank so I know something is wrong.

As for the drop in gas mileage I don't know what caused it? There is no check engine light, power seems normal if not even a little better than before I used the Marvel. Idle seems fine - no different than in the past. A few months back I replaced the EGR valve so I'm sure that is OK. My fear is that maybe the Marvel Oil created a problem? :smackface

Any suggestions or help would be much appreciated.

Thanks gang!
Edited by JDs96Metro, Jul 28 2012, 07:18 PM.
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JDs96Metro
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Oh, sorry, I forgot to add I will be changing the oil soon to get rid of the Marvel and old Oil.
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JDs96Metro
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Just thought - should I move this thread or repost in the 'Fuel Economy/Performance' section??
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rydholm11211
Big sky

check your compression, the marverl mystery oil could of done some damage if you had a lot of gunk in your enigne?
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Old Man


JDs96Metro
Jul 28 2012, 06:48 PM

Before I filled my current tank - I checked the oil. It was low so I put in a pint (not a quart) of Marvel Mystery Oil and added a quart of oil (5-30W like normal).
To "top off" your oil you had to add a quart and a half? (pint of MMO + a quart of the oil that you regularly use)----That means that HALF of your oil capacity was GONE.

Sounds like you were using a great amout of oil, even before adding the MMO.-----I dont think that MMO is your problem. I would suggest that you start by doing a compression check.....sounds like your engine is wore out?
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JDs96Metro
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Howdy all - thanks for the advice. Looks like I will be renting a compression test kit and checking that first.

Old Man - yeah, I was surprised how low it was but I believe the valve cover gasket leak contributed to the low level. I also wonder if there are other gaskets that are leaking too? I need to pull the timing belt cover and check. Before the drop in gas mileage it was running awesome.

I'll post the compression results once I test it.

Any other thoughts/suggestions are appreciated. Thanks everyone and have a great week!
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Nyquil-Junkie
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I suggest you put the MMO in the gas tank and not a leaky dirty high miles engine unless you want a lot more leaks.

MMO is going to dissolve all the crud plugging the cracks in your gaskets and seals. On the upside, the engine will be cleaner inside.
lol

Once you have good quality clean oil in your engine, there's not much point in putting in anything that's going to dislodge the crud keeping the thing from leaking unless you plan on replacing a bunch of seals & gaskets anyway. Good quality synthetic oil does a good job of cleaning all by itself all things being equal.

Put the MMO in yer gas tank... let your oil be free to be oil.
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