# MPG's are dropping quick **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** jetta, volkswagen, fuel-economy\ **Created:** [March 20, 2011, 7:53pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816 "2011-03-20T19:53:00Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![ruirietoo](https://avatars.discourse-cdn.com/v4/letter/r/cdc98d/32.png) [@ruirietoo](https://community.cartalk.com/u/ruirietoo)\ **Post date:** [March 20, 2011, 7:53pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/1 "2011-03-20T19:53:00Z")
drive a 2004 Jetta, and currently has 48000 miles but my MPGs for the city has dropped from 26-27 down to 14mpg. Has not missed any services. The symptoms started in the summer and the car had only 37000 miles on it. I took it to VW for a tune up and had the injectors cleaned, new fuel filters, new spark plugs, and air filter and added a can of 44k. That worked for one tank and now I am back down to 14mpg. ANY IDEAS? ---
**Author:** ![missileman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/missileman/32/1366_2.png) [@missileman](https://community.cartalk.com/u/missileman)\ **Post date:** [March 20, 2011, 8:01pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/2 "2011-03-20T20:01:23Z")
Have you had the Jetta checked for sticking brakes/parking brake? Have you checked the air pressure in your tires? These problems can cause a plummeting fuel economy in a hurry. Have you changed the way you calculate mileage? ---
**Author:** ![ruirietoo](https://avatars.discourse-cdn.com/v4/letter/r/cdc98d/32.png) [@ruirietoo](https://community.cartalk.com/u/ruirietoo)\ **Post date:** [March 24, 2011, 3:43pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/3 "2011-03-24T15:43:03Z")
Brakes are fine, tire pressure is spot on, did not change my calculation method. ---
**Author:** ![Goldwing](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@Goldwing](https://community.cartalk.com/u/Goldwing)\ **Post date:** [March 24, 2011, 3:53pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/4 "2011-03-24T15:53:23Z")
Thermostat is ok? Gets up to correct temp quickly? Smell gas anywhere? Exhaust look or smell different? ---
**Author:** ![ruirietoo](https://avatars.discourse-cdn.com/v4/letter/r/cdc98d/32.png) [@ruirietoo](https://community.cartalk.com/u/ruirietoo)\ **Post date:** [March 24, 2011, 4:04pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/5 "2011-03-24T16:04:49Z")
Thermostat never came into question, but that could be it. It has had multiple diagnostic done with nothing being found, other than a bad O2 sensor which was replaced. ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [March 24, 2011, 5:46pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/6 "2011-03-24T17:46:18Z")
On a daily driver I like to change the thermostat every 5 years or so, along with a coolant change. ---
**Author:** ![Bladecutter](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@Bladecutter](https://community.cartalk.com/u/Bladecutter)\ **Post date:** [March 24, 2011, 8:32pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/7 "2011-03-24T20:32:48Z")
Could also be time for a new MAF/MAP sensor, and PCV valve. BC. ---
**Author:** ![Goldwing](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@Goldwing](https://community.cartalk.com/u/Goldwing)\ **Post date:** [March 24, 2011, 11:06pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/8 "2011-03-24T23:06:48Z")
Any check engine light on? ---
**Author:** ![ruirietoo](https://avatars.discourse-cdn.com/v4/letter/r/cdc98d/32.png) [@ruirietoo](https://community.cartalk.com/u/ruirietoo)\ **Post date:** [March 25, 2011, 6:57pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/9 "2011-03-25T18:57:31Z")
check engine light has never turned on. ---
**Author:** ![ruirietoo](https://avatars.discourse-cdn.com/v4/letter/r/cdc98d/32.png) [@ruirietoo](https://community.cartalk.com/u/ruirietoo)\ **Post date:** [March 25, 2011, 6:57pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/10 "2011-03-25T18:57:56Z")
coolant was changed when I did the tune up ---
**Author:** ![ruirietoo](https://avatars.discourse-cdn.com/v4/letter/r/cdc98d/32.png) [@ruirietoo](https://community.cartalk.com/u/ruirietoo)\ **Post date:** [March 25, 2011, 6:58pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/11 "2011-03-25T18:58:47Z")
I cleaned it, but never replaced it. VW told me it is good. ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [March 25, 2011, 7:13pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/12 "2011-03-25T19:13:56Z")
What exactly is your calcultion method? It certainly sounds like the problem could be with that but I’ll reserve judgement for now. ---
**Author:** ![ruirietoo](https://avatars.discourse-cdn.com/v4/letter/r/cdc98d/32.png) [@ruirietoo](https://community.cartalk.com/u/ruirietoo)\ **Post date:** [March 25, 2011, 8:49pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/13 "2011-03-25T20:49:42Z")
Take the number of miles driven, divide that by number of gallons it took to fill the tank. EXAMPLE 200 miles/20 gallons = 10 MPG’s ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [March 26, 2011, 1:08am UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/14 "2011-03-26T01:08:28Z")
That’s the best way to calculate it but the EPA estimate for this car shows 21 in city driving. How did yours manage to best that by so much? Had the car scanned for any codes? At this point with limited info it would seem to me that if the engine were really running that rich there should be some codes stored. As to the CEL not being illuminated it’s debateable whether it would come on or not. In theory, yes. In practice, maybe or maybe not. Drivetrain slippage at work? (Auto trans on the way out or clutch slippage with a manual transmission.) ---
**Author:** ![ruirietoo](https://avatars.discourse-cdn.com/v4/letter/r/cdc98d/32.png) [@ruirietoo](https://community.cartalk.com/u/ruirietoo)\ **Post date:** [March 26, 2011, 7:27pm UTC](https://community.cartalk.com/t/mpgs-are-dropping-quick/62816/15 "2011-03-26T19:27:25Z")
To answer you EPA estimate for the car; the window sticker used the old estimate before the new estimate came into play. 25 city/30highway. Oddly enough the highway mileage has never been affected. I have had numerous scans and VW told me everything was in working parameters; check engine light never came on and the only code found was a faulty front O2 sensor which was replaced at the time of the tune-up and fuel injectors cleaned, and 44k was added [love that stuff]. That worked for 1 tanks of fuel which got me back to 26mpgs. I had tried 44k prior to the tune-up and it didn’t do the trick. Drivetrain is not slipping, but I think maybe the injector heads might be out of alignment, not positive. Thanks for your feedback.