Worried about freeway fuel consumption recently. Getting 16 MPG...

[G. COLTON]

Originally Posted by yogi799

What puzzles me is why the heck am I able to get 21-22MPG at 55mph and the mileage tanks at higher speeds if the spark plugs (or anything else for that matter) is not right?

And yes, I wanted to start using Premium again but in Ontario the price difference is huge and I did not know if it's worth it...

You are able to get all of those different mileages because you are using your onboard computer to read the miles per gallon.

It has been mentioned on this forum many times that it is necessary to manually calculate the fuel usage. A minimum of three (3) fillups is needed for this calculation.

George

[boston]

Mpg gets worse as speed rises due to aerodynamic resistance increasing.
Driving into a headwind does the same thing.



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[nsxtasy]

You've got several problems, and any or all may be contributing to your mileage problem.

1. Acura tells you to use PREMIUM fuel. Stop using regular. As noted above, whatever you save on the price of fuel, it's probably costing you more in reduced mileage.

2. It sounds like you have not been keeping up with the recommended maintenance intervals. (You have the original spark plugs after 140K miles??? ) The recommended maintenance schedule in the owner's manual should be your guide to what to do and when. However, if you're concerned about your gas mileage, you may want to do the services that have the biggest effect on mileage more often than recommended. Those would be the air filter and valve adjustment, and maybe the spark plugs.

As for the recommended intervals in the manual, some of the items need servicing based on mileage, others based on time, still others based on a combination of mileage or time, whichever comes first. Here are the recommended intervals for the most significant service items, according to the owner's manual:

• change oil and filter - every 7500 miles or 1 year, whichever comes first
• brake fluid - every 3 years regardless of mileage
• transmission fluid and transfer case fluid - first time at 45K miles or 3 years; after that, every 30K miles or 2 years, whichever comes first
• VTM service including differential fluid - first two times every 15K miles or 1 year; after that, every 30K miles or 2 years, whichever comes first
• coolant - the recommendation is 120K miles or 10 years, whichever comes first, the first time, and after that 60K miles or 5 years, whichever comes first. However this will be flushed (replaced) when they replace the water pump, and that will re-set your interval for changing the coolant
• air filter - every 30K miles regardless of time
• cabin dust and pollen filter - every 30K miles or 2 years, whichever comes first
• adjust valves - every 105K miles regardless of time
• spark plugs - every 105K miles or 7 years, whichever comes first
• timing belt (usually also includes water pump) - every 105K miles or 7 years, whichever comes first

3. Another item you should do is cleaning the EGR valve and ports, which isn't in the schedule but can affect the mileage.

On my 2004 MDX, with maintenance up to date, using premium fuel, and driving a steady 75-78 mph on a long trip, I typically get 18-21 mpg. Back home, it's more like 14-16 mpg in a mix of local and highway miles.

[yogi799]

Just drove back from Miami to Ontario. Same story as on the way south.
Same gas as two years ago and last year, same weight, more or less. Before, I was getting about 20 mpg at 70-75 mph. This year at 75mph, only 15-16. At 80mph+, the mileage tanks to 14 mpg and below. Disastrous.... Something is definitely wrong. I towed my new boat a lot in the last 2 years (not prior to that) so I wonder if that's in any way related to my reduced mpg over that period and the X has 140k now too. For towing, btw, I also felt that I was burning a lot more that others with comparable set-ups and rides.

Back to the X.

The air filter is new.

I will replace spark plugs soon. Not keeping any hopes too high on this one. Some members reported that iridium plugs are good for 200k at least. Some others are telling me the spark plugs will make a huge difference.

So is there a consensus that the valve adjustment is what I really need at this point (on top of the plugs)?? I'd rather get a few opinions on that one before I shell out several hundred $$$. If so, should I do this at the dealer?

[boston]

Those mpgs are spot on for the mph you are using.
Get used to it.


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[pianoman41]

Two things I haven't seen you mention yet: tire pressure and tire *weight* can be a big factor on mileage too. Unsprung weight is the enemy of HP and fuel economy. If your air pressure has dropped 4-5psi due to the cold weather up north here before you left it wouldn't be enough to trigger the TPMS light but enough to affect fuel economy. Also, not all tires in the same size weigh the same. Do you have the same tires on the MDX that you did for the first trip? I was amazed when shopping for replacement tires just how heavy some of the replacements were compared to the OEM tires. This will also affect fuel economy.

[boston]

Dead right.


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[nsxtasy]

Originally Posted by yogi799

So is there a consensus that the valve adjustment is what I really need at this point (on top of the plugs)??

When was the last time you had it done? Was it done less than 105K miles ago? If not, yes you really need to do it. As I already mentioned, it sounds like you've been skipping your regular maintenance, and your mileage may be one way you're paying the price. Also you should really do any of the rest of the scheduled maintenance services that are now overdue, including the transmission and other fluids, etc. Some could affect mileage. And even items that don't affect mileage - like changing the brake fluid - should not be allowed to extend beyond the recommended service intervals, for all kinds of reasons (safety, reliability, etc).

What you really need at this point is all three things I listed above: filling with premium fuel, bringing ALL the scheduled maintenance up to date if any of it is overdue, and cleaning out the EGR valves and ports.

If you're going to keep using regular fuel, then you may as well give up, since you're not even doing the most basic thing you can do to get better mileage and take proper care of your car.

Originally Posted by yogi799

should I do this at the dealer?

That's up to you. Any good independent mechanic - and I stress the word "good" - can do all of this work. You don't have to do it at the dealer. Independents are often (not always, but usually) less expensive than dealers. The quality of work varies at dealers, just as it does at independents, so what's key is finding a dealer or shop that knows what they're doing, is honest, etc.

Originally Posted by pianoman41

Two things I haven't seen you mention yet: tire pressure and tire *weight* can be a big factor on mileage too.

Tire pressure can be a big factor on mileage because it affects rolling resistance. Tire weight, no; any difference will be insignificant. Maybe on a 2000-pound sports car where you're looking for hundredths of a second per lap, but not on a 4500-pound SUV driven on public roads.

[Tyler]

I firmly believe spark plugs will make a big difference, check your psi too (as other memebers have mentioned). I do not think Valve Adjustment will help with gas mpg, I have 185,000 on my 03 and have yet to do one, and I still get 18.5 cruising at 70-80 (No that is not from the trip computer either.). IMO, I think you can do the spark plugs, without going to a shop..

[nsxtasy]

Originally Posted by Tyler

I do not think Valve Adjustment will help with gas mpg

That depends on whether they're out of adjustment, and how far. Just because yours may be within spec, doesn't mean his are.

Originally Posted by Tyler

I have 185,000 on my 03 and have yet to do one

And just because you're neglecting the scheduled maintenance on your car, doesn't mean it's a good idea for him to do so (or for you to do so, either).

[yogi799]

Peace guys... we're trying to get to the bottom of it and I appreciate all the advice.

Yes, sure I can do the plugs by myself. Will do it asap. Then, I will see and decide if the valve adjustment is next. The engine sounds brand new... really awesome. Starts perfectly and has all the power that it needs.

Weight... in the original post. About 3.5 adults and some cargo, few bags, not too much.

PSI... maxed out at 42psi (for fuel economy!!! LOL).

Tire brand - cheapest I could find, but still, some difference in their weight would not drop my mpg by 4-5.

Maybe it's my kids growing too fast??? Nah.. two years ago they weighted maybe 100-150 lbs less.

[Tyler]

Originally Posted by nsxtasy

That depends on whether they're out of adjustment, and how far. Just because yours may be within spec, doesn't mean his are.
And just because you're neglecting the scheduled maintenance on your car, doesn't mean it's a good idea for him to do so (or for you to do so, either).

Who do you think you are? Neglecting maintenance? I'm glad you know how I have maintained my cars. Typical know it all.

[nsxtasy]

Originally Posted by Tyler

Neglecting maintenance? I'm glad you know how I have maintained my cars.

Here are two FACTS:

1. Honda/Acura - the folks who built our cars - recommend that the valves be adjusted every 105K miles.

2. You have gone 185K miles without adjusting the valves on your car, according to your post.

Either one of these statements is false, or you have neglected to follow Honda/Acura's recommendations for scheduled maintenance and are 80K miles overdue on that service. FACT.

Originally Posted by Tyler

Typical know it all.

"Typical know it all", indeed. That's what I would call someone who neglects scheduled maintenance on his car, who thinks he knows better than the car's manufacturer when services should be done. At least, until problems start showing up due to the lack of maintenance.

[yogi799]

Spark plugs went like a breeze. 1h and all done. One was very loose... all the others super easy to remove. Now, I need to take it on a freeway to see if it helped any.

[Tyler]

@Nsxtasy it is not worth to fight with someone who must always be right!

@ Yogi, I really think that you will see increase in your mpg.