MPG problem for 1999 Ford V10 - Newmar Mountain Aire

LUV2RV-MN · 07-16-2011, 05:21 PM

Hi All,

Just purchased a 1999 Newmar Mountain Aire with 13,000 miles. Many of the emission components have been recently replaced and I had the Mass Air sensor replaced while driving home, that really helped improve mileage but my overall was not great - 5.8 mpg.

For all of the Ford V10 experts, what things should be checked out which could affect mileage? What needs to be tuned up on an engine with EFI?

Ray

SteveLevin · 07-16-2011, 05:40 PM

It sounds like you are on the right track, but let me ask... how fast are you driving? Speed can make a huge difference in mileage. If I push 70mph I get about 6mpg, but at 58 I get 8.5.

Steve

LUV2RV-MN · 07-16-2011, 07:40 PM

Hi Steve,

I held at about 61 to 62 mph. The last leg I drove 70 but I haven't filled the tank for the last leg and haven't calculated that into the average. I'll try 58mph and see what can of success I have there. I only had about 1/2 tank of water and a small suitcase of clothes and a few tools. I haven't taken time to run it across a scale and see what it weighs.

Ray

Superslif · 07-16-2011, 08:09 PM

Speed kills...That's gas mileage I'm taking about. Even pulling a trailer the difference between 58 and 68 is huge. At 58-59 I can stay in over-drive at about 1800 RPM's with a semi-flat road. I actually do best on secondary roads where the speed limit is 55mph with some hills. I'll pay the 10 cents extra and fill up with one grade higher octane. It will help to stay in over-drive. In my tow vehicle there is a on-board MPG read-out that updates every 15 seconds....

SteveLevin · 07-16-2011, 09:34 PM

I will say that my gut says that's poor mileage for 61-62mph. What's the GVWR on your coach? That'll at least get you in the ballpark... mine is a 17,000 GVWR running at about 14,800 on the scales right now.

Steve

HoRotica · 07-16-2011, 10:11 PM

My 1999 GS SunSport averaged 7.5 @ 75-80mph... Not running the AC (early March trip from PA to Florida).

Have you been running the chassis AC?
Chris

LUV2RV-MN · 07-17-2011, 09:44 AM

Hi Chris,

Yes, I was running the chassis AC. I tried running the Generator and the roof AC and it seemed like my fuel gauge was dropping faster - I have checked the generator literature and it should use .7 to 1.3 gph of gas. One thing that I miss on this coach compared to the 04 Discovery DP that we had is an amp meter showing how much load there is on the generator.

Ray

LUV2RV-MN · 07-17-2011, 07:26 PM

I was out doing some fixing and looked under the hood. The wires that go to the AC clutch are disconnected from a small switch or relay on the air conditioner itself and are attached to a couple of new blue wires going through the dash. Looks like someone modified the circuitry - I need to trace the wires and see what is going on. It did seem to me like the air conditioning was on regardless of the position that I had the switch.

LVJ58 · 07-18-2011, 10:52 AM

Hi Ray,

After looking up your coach model I see it's 37'6" in length and I would suspect weighs in excess of 18,000lbs loaded for travel. With the 1999 275hp v10 your low fuel mileage may result from your coach being somewhat underpowered.

A couple of things you might try is installing a set of headers, i.e., Thorleys, Gibson etc. along with a 3.5" exhaust system using low restriction muffler like Flowmaster, Magnaflow or Dynamax.

This should increase your HP somewhat also you might consider Brazel's Ultratune or 5 Star Tuning custom tune for your PCM.

Our coach is 37'8" long weighing 21,230lbs loaded for travel and we tow a 3,000lb vehicle. We usually maintain a driving speed of between 55 & 60mph and overall mpg averages 7 over our 11 years of ownership.

You have a great quality coach with your Mountain Air.

Enjoy many fun, safe and trouble free journeys

Stump Jumper · 07-18-2011, 11:16 AM

I'll second what LVJ58 had to say. We average about 7 mpg with our 2000 Bounder 36S.

Camping4fun · 07-22-2011, 06:46 PM

Just got home from Myrtle Beach going there we went over Monteagle coming home through the mountains of Tn with a 4900 lb toad and running 70-75 we got 6.1-6.5 mpg.

frankdamp · 07-22-2011, 07:59 PM

We're seeing about 7.9 mpg at sea level with our 02 (01 chassis) V-10 32' Georgetown. Haven't done much high altitude stuff, which was a killer on our old carburated Ford 460 (about 4.5 mpg).