Those who have solar on the roof, have you noticed a change in MPG?

neoneddy · July 30, 2018, 08:53:04 AM

Attached is what our rig looks like now. I've noticed a drop in my MPG since last year, I've only owned it for 18 months or so but I have 4000 miles or so on it over that time.

I'm wondering if others with similar setups have noticed anything or am I silly for hoping for better mpg. Last summer I was seeing 6, 7 or even 8 mpg one time. Now I saw 6.3 once and the rest has been 5.5 or so, lots of hills and starts and stops though. This last trip was 5.66 mpg over 583 miles and we moved everyday, so lots of airing up time every day. I try to cruise around 63-65 on the interstates, and posted anywhere else. I run my tires pretty firm, 100-110 all around.

What has changed since then?

Added roof rack and solar - added air resistance, thinking of adding air dams or some sort of skirting to clean up the air flow.
Built out more / added significant weight, not sure how much quite yet.
Adjusted throttle linkage to get more pedal travel - this could be it here as well. I still don't hit WOT even now, but before I'd say at best I got 65-70%, now I'm at 80% or so I'd say. I could just be accelerating too fast, but I feel like I'm just turtling along most times.
Did have that over heat in the black hills, but this trend has been going on since before that.

I'm calculating my mpg by entering in the milage from my hub odometer into a spreadsheet, but I'm starting to also question if that is accurate. I also have a GPS with trip odometers, I think I should cross reference the two to verify my data.

Any other ideas? Is this just the way she goes?

luvrbus · July 30, 2018, 09:03:38 AM

5 to 6 mpg is about the average on 6v92 in hills,they are just a 9L engine

chessie4905 · July 30, 2018, 10:12:15 AM

Are you towing that vehicle in picture? What is your coaches total weight now? Mileage sounds about right in the range. Quality of fuel could effect it also.

neoneddy · July 30, 2018, 10:15:13 AM

In south dakota on I90 I did, on our most recent trip no. I only saw a .2 to .3 mpg difference with or without the toad. Last year it was almost a 1 mpg difference.

I don't know my weight currently, I know it's going up, we keep putting things in it. Just finished a tile shower, I bet that helps.

chessie4905 · July 30, 2018, 10:43:07 AM

Do you fill to top of neck? Consistency on filling tank makes a big difference. How many gallons to raise fuel level 1 inch. Parking level every time filling it. You are probably working the engine more on grades now that you are getting used to it, and especially after changing max throttle setting. Headwinds or tailwinds change it also. And of course total weight.

Fred Mc · July 30, 2018, 11:44:24 AM

ALL of the items you mentioned contribute to a reduction in mileage. weight, inclines, stop and go etc.

My solAR Panels are, at most, 5 " above the roof line. I would suspect that solar panels would increase drag a little but probably not even calculable.

Fred

luvrbus · July 30, 2018, 12:10:32 PM

Could be the fuel, the usage goes up when going from the 5 % bio to the 20% bio diesel,if you bought from a major truck stop like Loves you bought some cheap crap at a high price

Geoff · July 30, 2018, 12:56:27 PM

Who was that guy from Texas that poured his dirty engine oil in the fuel tank? That will lower your fuel cost.

Lee Bradley · July 30, 2018, 02:07:01 PM

Quote from: neoneddy on July 30, 2018, 08:53:04 AM
Attached is what our rig looks like now. I've noticed a drop in my MPG since last year, I've only owned it for 18 months or so but I have 4000 miles or so on it over that time.

I'm wondering if others with similar setups have noticed anything or am I silly for hoping for better mpg. Last summer I was seeing 6, 7 or even 8 mpg one time. Now I saw 6.3 once and the rest has been 5.5 or so, lots of hills and starts and stops though. This last trip was 5.66 mpg over 583 miles and we moved everyday, so lots of airing up time every day. I try to cruise around 63-65 on the interstates, and posted anywhere else. I run my tires pretty firm, 100-110 all around.

What has changed since then?

Added roof rack and solar - added air resistance, thinking of adding air dams or some sort of skirting to clean up the air flow.
Built out more / added significant weight, not sure how much quite yet.
Adjusted throttle linkage to get more pedal travel - this could be it here as well. I still don't hit WOT even now, but before I'd say at best I got 65-70%, now I'm at 80% or so I'd say. I could just be accelerating too fast, but I feel like I'm just turtling along most times.
Did have that over heat in the black hills, but this trend has been going on since before that.

I'm calculating my mpg by entering in the milage from my hub odometer into a spreadsheet, but I'm starting to also question if that is accurate. I also have a GPS with trip odometers, I think I should cross reference the two to verify my data.

Any other ideas? Is this just the way she goes?

I would use the hub meter. Even if the is off the actual mileage it will be consistent and that's what you want for checking MPG.

I'm sure my mileage is up since added solar because of the reduced alternator load on the engine but I think the fuel evaporation from the tank is hiding the gain.

Iceni John · July 30, 2018, 02:24:13 PM

Even with eight big grid-tie panels on the roof, I don't think they will change my bus's MPG one jot. For a slab-fronted vehicle with the aerodynamics of a brick $hithouse that cruises at only 60 MPH anyway, my PV panels are irrelevant to its fuel consumption! The few hundred pounds of extra weight is again probably insignificant for a thirty-odd thousand pounds bus. You mentioned several other things that could change your fuel consumption, but solar? Nah. One thing you didn't mention - in summer the fuel is hotter and less dense, and therefore less energy-dense, so each gallon has less BTUs and will make less power. Is that calculable?

John

windtrader · July 30, 2018, 03:24:43 PM

In certain situations, added solar could improve mph if pervioulsy using the generator a fair bit to charge batteries. For example, boondocks in one place for a week, running the generator 4 hours a day uses around 14 gallons (.5 gph). If drawing from the main tank, that will have noticeable effect depending on distance between taking calc.

neoneddy · July 30, 2018, 08:13:22 PM

I have generally been buying from truck stops. We'll see what this tank will have in store.

I'm adding a tach and a boost gauge this week to help the idiot behind the wheel behave himself more. I had a car with a turbo and instant MPG calculation, anytime I got into the boost it would drop quickly.

chessie4905 · July 31, 2018, 03:32:27 AM

A pyrometer will give you a better idea of how much fuel your inputting into engine. Boost is also good to have. Can indicate issues with engine or fuel system.

uncle ned · July 31, 2018, 07:44:13 AM

If your coach is anything like Huggy. The only thing that changes the fuel mileage is the right foot.

She gets 6 to 7 if I keep my foot under control.

If i let my right brain get control she drops down to 2 or 3.

And stay off of the inter-state hy. they eat fuel.

uncle ned