"NewToMe" Monaco loves diesel fuel!

[RickGyver]

I love this moho but it uses way too much fuel! My other Cummins 8.3 got 11+ regularily with identical drive train and weight. Current cummins is 300hp and old was 250hp. Both with 6 spd allison. This 1995 Monaco Dynasty doesn't smoke, starts well and has plenty of power. I am afraid to do the math but I'm guessing the mileage is under 6 mph. I'm thinking 9/10 mpg would be more normal for this rig. I rarely go over 60/65 mph. Odometer reads 60k so parts aren't worn out. Maybe will put it up on blocks! thx

[Dixieray53]

11 plus Did you run the geni ? Were you towing anything...How big was the old RV? Was it a FRED? I have only been rv'ing only 8 years have never had a Class A get more than 8 mpg. Our Cat 360, Allison Trany gets 7.5 every time every gallon. We run the geni and tow the 2010 Flex....Let us know if you fiqure it out... Peace D

[srydve]

6 is way too low. We just completed a trip over 3000 miles, back and forth over several mountain passes, sea level to over 8000' , some days we fought some pretty strong winds too. Towing a 3500 lb. toad and driving 60-65 mph. I just calculated that we averaged over 8 for the whole trip. On fairly level freeway runs we got 10. We have the 300hp 5.9 cummins and 6 speed allison. I don't what could be wrong with yours, air filter comes to mind, but something is definately not right.

[JimM68]

250 and 300 HP? Are you sure we're talking about 8.3's and not 5.9's?

[jimkate]

The 8.3C Cummins engines in 1995 were produced in Monaco coaches as 250HP in coaches less than 40', and 300HP in coaches 40'long and longer. Most people had the 250HP engines upgraded to 300HP because all the internal parts were the same.

Mileage: somewhere 7 and 9 would be considered in the normal range. Much below that should indicate something wrong. Much above that should be unbelievable.

[H. Miller]

We have the 8.3 - 330hp with the full Banks kit (supposed to help mileage) and are happy @ high 7's @ 65 mph with toad & 32,000lb gross.

[RickGyver]

Let me add the following; this rig sat in a storage lot for years. Not sure how that would effect performance. Changed air filter and all fluid filters. New tires were inflated to 105 front and 100 rear. Never travel with full water. No long, uneccessary idling except when bags are airing up, which is a huge waste of fuel. Generator is used minimally. This is absolutely a 300hp 8.3 cta with no throttle plate. My gas moho's got better mileage than this DP!! I haven't checked for exhaust restrictions. thx

[Robi.1014]

Let me suggest looking for fuel dripping on the ground!.....but I don't mean when you're standing still. Assume for the moment that a full fuel tank might be burping and or sloshing fuel onto the ground while you're driving, but when the tank is down to 2/3 or so, the fuel dumping stops. So to test this theory, try several "fill ups" where you fill the tank only to 3/4 full.....then check the mileage under this condition. My Dip averages 8.3 consistently.

[letsgo]

We have the 400 isl cummins 40 ft. H.R. imperial get 10.5 to 12.4 on a regular basis, engine runs 1.500 rpms at 65 m.p.h. towing a jeep liberty,

[Mekanic]

I am guessing with the sitting the muffler might be part way clogged with rust. it would idel fine but the more air you are trying to push though it the more ithold it back.
Hit the bottom of the muffler in several differnet places with a rubber mallot and then listen for loose rust particles bounching around.

[JimM68]

Love these mileage threads...

fyi... mine is an 08, with the particulate filter emissions, 350hp.
When I bought it with 18k miles on it, the computer showed lifetime mileage at 6.0 exactly.

I've been able to get 6.7 - 7.0.

My previous 99 PA, 275hp 20 valve V10, got about 5 mpg.

No comment on many of the mileage claims I read on the internet.

[RickGyver]

Quote:

Originally Posted by Robi.1014 Let me suggest looking for fuel dripping on the ground!.....but I don't mean when you're standing still. Assume for the moment that a full fuel tank might be burping and or sloshing fuel onto the ground while you're driving, but when the tank is down to 2/3 or so, the fuel dumping stops. So to test this theory, try several "fill ups" where you fill the tank only to 3/4 full.....then check the mileage under this condition. My Dip averages 8.3 consistently.

Thx but dripping fuel going down the road would show up on the rear cap.I have none of that.

[RVRon]

Maybe take it to a Cummins distributor for a thorough check up, run the rack, check the fuel pump etc. 60,000 miles is not an insignificant number on a MH. A lot can go out of calibration in 16 years too.

[William Willard]

JimM68 -- Yea, these mileage threads are amusing -- We`ve had motorhomes with a 8.3-250hp, Cat300hp, 8.3-325, & 2, with the 400ISL ,& if I got 8mpg on any of them I was overjoyed -- We`ve been RVing 31 years, & I drove Big Rigs OTR for 12 years, so I know how to drive -- I don`t go by what some electronic flow meter reads, I go by miles driven, divided by gallons used -- I did get above 8 one time, going down Donner Pass with a tail wind -- Bill Willard