I have a 99 GLE that just turned 100,000 miles. I was getting roughly 420 mpg each tank for along time and now it has been droping consistantly to around 400 then 380 and now about 340 mpg. Anyone got any good ideas on what is wrong or what I could replace.
Thanks.

 

My '99 GLE has 143,xxx on it and I am averaging about 22mpg. When she was new I would get 23mpg so I don't feel too bad about losing 1 mpg. As to what you could do to increase the mpg I would suggest a new fuel filter, plugs, synthetic oil and quality filter. I also run 93 octane 90% of the time and I throw a bottle of Red Line fuel system cleaner once or twice a year.

Of course driving slower might help...but what fun is that???

 

I would say to first just check all the usual suspects like your filters, exhaust, gas type, plugs, tire pressures, and even your driving style and location lately. Make sure you aren't leaking any fluids or having anything burning in the exhaust (different colored exhaust gasses). I just got my max a month ago at 108,000 and she gets about 350 miles per tank in the city and almost 440 on the highway so it might just be a thing around that age.

And by the way, I think you mean 400 miles per tank, not 400 miles per gallon (mpg).

 

At 100,000 miles, you are a bit overdue for a tune-up. Have you done the 90k? Or even the 60K? If not then that would be your problem.

 

what is all included in the 90K?

 

Check the oxygen sensors also, they're always causing trouble.

 

Yea...i hate those guys!

 

Don't know if you have gotten any codes yet but check if the knock sensor is functioning properly.

 

if your vehical has never been through a knock sensor, take it out, and check it for consistancy, and if it appears cracked or damaged, replace it. it rob's your car of atlease 15% of horsepower.

 

Yeah, that is what I would say to check.
I get about 23mpg (mostly in town with some highway driving mixed in there). That is not bad for how much fun I have driving all the time.

 

Plugs, all filters, coolant, tranny fluid, pcv, oil change...most likely other stuff I've forgotten.

*edit* Belts too.

 

my 96 has 106k. on freeways i average 26-27 mpg. i get about 340miles on 3/4 tank. i usually don't wait till empty to fill up.

 

My car gets around 18mpg with mostly city driving. I actually got almost 28mpg on my last trip to Northern California, ofcourse this was all freeway and cruising around 75mph. I actually checked my calculations twice.