loid1929

I'm not a mechanic -

I have a 2005 Navigator with 91,000 miles...on a recent trip (tonight) I registered 13 MPG on highway driving...Used cruise control, drove 60 MPH, and had only 3 people in the car (very little gear). It was 7 degrees outside.

On summer road trips in the past (with 6 people and a ton of gear) I registered 18MPG on the highway...

Just had it serviced...oil change, fuel filter change, new air filter...tires rotated, and alligned...all are properly filled...

My service guy told me the oil was low almost 2 quarts since the last oil change...told me to check the oil when I gas it up...He also suggested changing the transmission fluid and the rear differential fluid.

Am I stuck with poor MPG based on the age of the vehicle, or is there something I can do to improve it? Other threads discuss Magna Flow exhaust, and dual electric fans...


Since the engine is burning oil, does this hurt MPG?

What about better gas, I routinely use 87 octane, or the "cheap gas"...should I bump up to the "good stuff" ?

What about the fuel injectors? Should I get them cleaned?

I'm willing to try anything, the vehicle runs great, and looks brand new. Since I have 4 kids, and a boat, there are few choices that handle our families needs...

R.S.LOGAN

Depends on mileage since last oil change / check , whether that amount of oil used is a concern or not . Would have thought it was advisable at that mileage and when servicing car to replace spark plugs and also oil filter .

NoLeaks2001

As far as I know everybody gets worse mileage in cold weather for a number of reasons. An engine running on 9 degree air is going to get much lower mileage than when running in 80 degrees. Plus the gasoline is a "winter blend" in many areas which has a lower energy content (I have read).
Additionally and this may be a slight influence just based on common sense, If the ambient air is 9 degrees, it will be more dense and require more effort to push a vehicle through it at freeway speeds.

As for the oil usage, I don't know how many miles since your last oil change. Are you using the grade recommended in the owners manual? Two quarts seems high and if there isn't a leak some place, I would check a plug to see if there is fouling.

NoLeaks2001

Also,according to the EPA your vehicle is designed to run on 91 premium fuel.

www.fueleconomy.gov

Hamfisted

Are you the original owner? When's the last time the truck was washed and waxed ? A good claybar and wax job will make it slip through the air a lot easier. If you leave it dirty all the time it's like trying to slide sandpaper across the kitchen counter top. These things are about as aerodynamic as refridgerators so anything you can do to help that will provide direct results. As far as cleaning the injectors I would just go by Walmart and get a couple of cans of Berryman's Chemtool cleaner and pour them in the tank before your next fill up. Make sure your tires are inflated correctly. A Flex-a-Lite #270 electric fan kit is about $550 if you want to spend the money on it. If you can't install it yourself it'll run you another $100 to get it installed. Takes a long time to recoup the investment in fuel savings though. When you replace your tires get some that are low resistance rated like the Michellin LTX M/S 2's. Not the cheap ones.


- Mike

NoLeaks2001

BTW I DID NOT put that little yellow guy on that post.I have no clue about how it got their,I don't use those things.

Cheapshot

Loid,

At 91,000 miles it does not surprise to see that your gas mileage is starting to decrease. With age on a motor comes wear and tear (Motor leaks, worn piston rings, and valve seals not sealing as well as they did before when it was new).

#1) You need to keep in mind that a lot of gas stations are cutting their fuel with ethanol (E85 fuel) to help keep costs down on product while still charging us an arm and a leg. Different motors not designed to burn ethanol behave differently with fuel mileage. I would suggest trying to find a gas station that does not cut regular gas with ethanol and run that through your tank for awhile and see what happens. Remember the higher the octane rating of the fuel is, the hotter it burns, slower it burns and more controlled / or complete it burns. Use what is recommended by the manufacturer.

#2) When was the last time you had all the spark plugs / plug wires replaced. If you haven't had that done for awhile you may want to think about having that done soon.

#3) It may be time to have the differential fluid drained out of the rear axle as well and have it refilled with good fresh oil. If the gear oil is getting old and starting to gel it could be having an additional small influence on your mileage. Believe it or not small metal filings are possible when you have a ring and pinion gear constantly grinding against each other (Especially when towing). When you get enough filings the oil cannot do its job as well.

#4) Depending on your location, when the weather gets seriously cold, don't be afraid to use different motor oil. If you are using motor oil rated for 30 degrees try using oil rated for 20 degrees for the remainder of the winter season and see what it does. Also, if the motor is losing oil (2 quarts between oil changes) like you said, this means more metal to metal contact between all the moving parts inside. Be sure to keep an eye on it and keep the oil at the required level.

#5) Do not rely on the computer fuel mileage counter if your vehicle is so equipped. Anytime I take long trips I fill the gas tank up and record how far I travel on 1 tank of gas. I'm sure you know how to calculate that but for anyone else who may not know and reads this, its the amount of miles driven divided by the amount of fuel in gallons it takes you to refill the tank. So if you drive 325 miles and it takes 20 gallons to refill the tank, you drove 16.25 miles per gallon of gas. Basically I'm saying you may have gotten better fuel mileage than what the car thinks it got.

After any combination of these items are complete, start watching your mileage and see what works and what doesn't work.

Hopefully one of these can help you out, the fuel mileage situation sucks especially with the price of gas steadily climbing. We all feel your pain.