Does a clean vehicle get better MPG than a dirty one?

[raineman]

Interesting quandary. Found some interesting things when researching this concept. Wondering how/if a dirty MH, travel trailer or 5th would be impacted.

From the Science Channel's Myth Busters:
Dirty Cars Are More Fuel Efficient | MythBusters | Discovery
Finding: BUSTED
Explanation: In 2002, an engineer named Tom Wagner Jr., in an article on money-saving tips, reported improved fuel efficiency after giving his car a scrub down. And ever since, auto experts have debated whether the opposite might be true. But the MythBusters scored a point for the enterprising engineer by proving that the only money you'll save motoring around in a dirty car is quarters at the car wash.

People driving the dirty car myth argue that the grimy coating improves aerodynamics, much like the effect of dimples on golf balls. Those tiny divots disrupt air particles as they flow across a golf ball, reducing wind resistance — also known as drag — and sending it sailing 37 percent farther than a smooth ball would travel.

But randomly distributed dirt particles do just the opposite on cars, creating more drag as air particles cling onto the grime. According to MythBuster calculations, that filth effect cuts fuel economy by around 10 percent.

If only that dirt could magically form a golf ball-like dimpled shell on a car's exterior, this myth would be a hole-in-one.



https://mythresults.com/dirty-vs-clean-car

MythBusters Episode 127: Dirty vs. Clean Car
Premier Date: October 21, 2009

A dirty car is more fuel efficient than a clean car because the dirt makes the car more aerodynamic like the dimples on a golf ball.
BUSTED (CONCEPT PLAUSIBLE)

Adam and Jamie covered a car in dirt and mud and drove it down a track at highway speeds to measure its fuel efficiency, and repeated the test after the car was cleaned. They discovered that the average gas mileage for the dirty car was 24 miles per gallon while the clean car performed better at 26 miles per gallon. They then tested the reasoning behind the myth, and tested how well dimpled golf balls performed against smooth balls. They discovered that dimpled golf balls could fly almost twice as far as smooth balls. Dimpled balls disrupt the air around them, creating a smaller wake behind them and reducing drag. For a full-scale test, Adam and Jamie put a layer of clay on a car and did two more sets of runs on their track – one with a smooth clay surface, the other with dimples pressed into it. The respective fuel efficiencies were calculated as 26 and 29 miles per gallon. Although the original myth was invalid, the theory behind it was sound, leading to a final judgment of “Busted, Concept Plausible”.



https://medium.com/@reza_keshavarzi/...ent-d0591d58f5

[Old-Biscuit]

I know my truck drives better and gets better mileage right after I wash/wax it.
Same improvement occurs after oil change also.


Max affect......wash/wax & oil change at same time.


Course that is seat of the pants affect..no scientific data


Should see the effect when I get haircut right after was/wax/oil change...it's dramatic

[grindstone01]

My Chevy truck gets better MPG after a good wax job. I do admit it's more related to my mood of being more relaxed and tired from waxing the truck which probably slows my driving speed.
On a serious side, it makes sense that a smooth waxed vehicle will slip through the air restriction easier, but the savings are probably measured in 1/10 MPG savings at best.

[ronspradley]

Absolutely better fuel mileage. Slips thru the air easier. And the driver sits higher in the seat, reducing unslung weight, thus reducing fuel consumption.



ronspradley

[Bob_C]

Do you see dirty race cars?......

[twinboat]

Originally Posted by ronspradley

Absolutely better fuel mileage. Slips thru the air easier. And the driver sits higher in the seat, reducing unslung weight, thus reducing fuel consumption.



ronspradley

The DW believe that. That must be why she stores the canned goods, pots pans and dishs in the upper cabinets.

[BirchyBoy]

Originally Posted by bob caldwell

Do you see dirty race cars?......

Sponsors don’t like dirt covering up their logo. Especially Tide.

[Bob_C]

If dirt worked, that'd change!.....lol

[Waiter21]

We had this discussion regarding aircraft about 30 years ago.

On the LongEZ aircraft, no difference. HOWEVER, One exception: In cases where the LongEZ (VariEZ) used the older "GU" canard airfoil, (Mine used the newer "Rontz" airfoil) If the leading edge was covered in dead bugs, this could affect the lift performance of the airfoil.

It was determined that a large buildup of dead bugs tripped the boundary layer at the leading edge. Rain would do the same thing.

http://www.iflyez.com/


As for a RV, or a car, or truck. no difference....

[Ray,IN]

So, the bottom line is; only wash N wax the hood and front fenders. This maximizes the feel-good effect while minimizing effort of uselessly engaging in work.

[Cat320]

Dirt on a vehicle is drag, less drag better MPG.

[stepside454]

Can’t testify about dirt, but our car is covered stem to stearin in hail dents after 2 major hail storms last summer . We picked up at least 1 mpg according to onboard computer

[MotorPro]

Another thing that people claim will pick up 10% gas mileage . With synthetic oil and special spark plugs and all the other claims you guys must get over 40 mpg.

[twinboat]

I've added so many gas saving tricks that I have to let gas OUT of my tank after a trip.