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joes2901 · 07-16-2012, 10:20 PM

When I refueled with 88 and then 91 Octane gas my 2012 RV (towing at 24,300 pounds and only 3,500 miles on the new RV) with a 2012 F53 V10 engine lost the marbles it was rattleing and the coarse noise it had when climbing steep mountain grades on N/B I-15. However the gas mileage was poor. It went from 6.09 MPG on 87 Octane from So. Calif to St. George, UT. After an 88 Octane fillup the mileage went to 6.57 MPG to Rock Springs, WY but the engine seemed to be a little smoother and quieter. After an 91 Octane fillup the mileage increased to 6.82 MPG on the way to Gillette, WY the marble rattleing was gone and the engine was much smoother and quieter. A 91 Octane refill gave the same engine performance but the mileage droped to 6.03 on the trip to Grand Teton NP. I used less cruise control, and used the accelerator to force downshifts for the 2 steep grades (over 9,600 feet) to Grand Teton, NP.

Is this typical for a new Ford V10?
How many miles for the breakin period before the V10 can produce 8+ MPG?
Do you spend an extra $14 per tankful for 91 Octane gas in order to reduce or eliminate the V10's rattleing and pinging?

Mr_D · 07-16-2012, 10:29 PM

According to studies done by Cummins it takes 140,000 miles to establish accurate fuel mileage figures. Short trips and one tank checks are no where near accurate.

I'd have the engine checked, it shouldn't knock on regular unleaded no matter what elevation you're at.

Chuck 1935 · 07-16-2012, 11:24 PM

Quote:

Originally Posted by joes2901

When I refueled with 88 and then 91 Octane gas my 2012 RV (towing at 24,300 pounds and only 3,500 miles on the new RV) with a 2012 F53 V10 engine lost the marbles it was rattleing and the coarse noise it had when climbing steep mountain grades on N/B I-15. However the gas mileage was poor. It went from 6.09 MPG on 87 Octane from So. Calif to St. George, UT. After an 88 Octane fillup the mileage went to 6.57 MPG to Rock Springs, WY but the engine seemed to be a little smoother and quieter. After an 91 Octane fillup the mileage increased to 6.82 MPG on the way to Gillette, WY the marble rattleing was gone and the engine was much smoother and quieter. A 91 Octane refill gave the same engine performance but the mileage droped to 6.03 on the trip to Grand Teton NP. I used less cruise control, and used the accelerator to force downshifts for the 2 steep grades (over 9,600 feet) to Grand Teton, NP.

Is this typical for a new Ford V10?
How many miles for the breakin period before the V10 can produce 8+ MPG?
Do you spend an extra $14 per tankful for 91 Octane gas in order to reduce or eliminate the V10's rattleing and pinging?

If the manuel says use 87 Octane fuel and it rattles, the timing is set too far advanced. You should have the Ford dealer check it.

LVJ58 · 07-16-2012, 11:35 PM

Can't speak for the later model 3 valve v10's but the v10 engine in our 2000 coach runs smooth on 87 octane climbing 6-7% grades. It would appear your fuel mileage is in the normal range for the combined weight you posted.

The combined weight of our 37' coach and toad is 24,830 and our mileage is about the same as you're getting. Occasionally I'll get 7mpg between fill ups.

Insofar as the PCM is programmed for 87 octane I see no advantage of using and paying extra for a higher octane fuel, but if it works for you I guess it's OK.

As Mr_D suggested if you're getting pre-ignition knock when under load, you best have a diagnostic check done on your engine as you may have a problem that could result in costly engine damage.

Good luck and safe travels...

chuckftboy · 07-17-2012, 08:18 PM

I also run with just about the same weight when towing. Use only 87 and no engine knock what so ever. As for the mileage I average 6.1 and it doesn't change much with any change in speed, hills or not. You may never see 8 mpg, V-10's just love fuel.

HabitatGuy · 07-17-2012, 08:36 PM

On a recent trip including flats, rolling hills and ozark mountains, I averaged from 6.1 to 6.4 mpg with similar weights as previous posters. The only significant change was while running generator all day on a hot day. That caused me to slip to 5.85. It seems with weights like that mid 6's is about it.

Rockcrawler · 07-18-2012, 07:08 AM

Timing is computer controlled, for the most part. Something is wrong for sure. There is a knock sensor on most newer gas motors that detects the "ping" long before our ears do. This sensor tell the computer to back-off the timing. Sounds like you need someone to pull error codes on the computer.

Good Luck!

Topflite51 · 07-18-2012, 09:29 AM

First of all, who told you to expect 8+ MPG with a Ford V10 in a MH?

With higher elevations, the octane requirements are less than they are at sea level if you are experiencing pinging/engine knock you have issues with your ecm and best have it checked ASAP.

Damon Outlaw · 07-18-2012, 09:44 AM

I think a little light knocking/pinging while towing behind your motor home up steep mountain grades under full acceleration would not be unexpected. However, more than that should be looked at.

My current high mileage with regular unleaded without towing is 8.8mpg (twice) at about your weight and 13 ft tall, but have to credit the modifications listed in my signature for around 1 mpg improvement.