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Wash Car for better MPG?

Please solve my debate with my wife. Does washing your car give you better MPG on the highway? If it does, how often should we get our new Yaris washed on a road trip to the Grand Canyon? Assuming 99% highway miles and always getting the most basic car wash (usually about $4 with a fill-up), what’s the best frequency of washes to save money on gas without spending all that savings on the car washes.

In theory, yes. In practice, I think that the additional gas mileage that you could gain would be so miniscule as to be unmeasureable in real terms.

Since your car is new, you do want to keep it clean, for the benefit of the paint. I would suggest that you just wash it as often as its appearance dictates, and not think about the theoretical gas mileage benefit.

I agree, unless your car is incredibly dirty, you won’t notice the difference. Setting the cruise control just one mile per hour slower will make a much bigger difference in the real world, so will inflating the tires a few psi more. You’re better off putting that $4 into the gas tank.
The biggest improvement in gas mileage by far comes by changing the nut behind the steering wheel. A manual transmission Yaris should deliver 40+ mpg if there are no headwinds and you take speed limits literally. My best tank so far has been 45 mpg.

I usually pay extra for the premium car wash simply because the wax seems to make my car stay clean longer. With the basic soap and rinse, it seems like the car is dirty again in no time.

You are so right, driving behavior probably effects fuel efficiency more than anything. 45 mpg for the Yaris…wow, that’s pretty good for a contemporary non-hybrid car. I’m looking for something to replace my '94 Subaru Justy (ca 40-45 mpg).

Let’s be realistic. Washing does not improve fuel economy. In fact, if we include the extra gas used in unnecessary trips to the car wash, your mileage drops! Or if you simply add in the cost of excessive car washes at each fill-up, your car expenses soar.

I don’t know which of you has proposed this wacky idea in the first place. Nor do I care. Just drop it and enjoy your vacation.

Desperate times, Steve, desperate times.

Maybe some of the water from the car wash could be electrolyzed into hydrogen and…

…because the wax seems to make my car stay clean longer…

The wax they use in drive-thru car washes is nothing more than mineral oil and water with a little fragrance to make it smell nice. The benefits to your car’s finish would be negligible. The benefits to the car wash owner’s bottom line… priceless!

The 0.001 MPG increase that you see will not make up for the eight minutes or so of idling in the car wash (assuming it’s an automatic).

In fact, if we include the extra gas used in unnecessary trips to the car wash, your mileage drops!

What extra trip…you mean backing out of my garage into my driveway??? 8*)

VDC is right…In theory yes…but there’s no way you could ever measure the difference. Maybe over a 10k mile period if you kept it cleaned and waxed it could probably save you 2-3 miles TOTAL.

I am not quite so quick as others to dismiss this idea, because I have seen the effect of washing a small aircraft (test vehicle - Beachcraft Bonanza). Washing a dirty Bonanza increases top speed and improves fuel economy enough to pay for the wash on the first trip.

Given the speed and aerodynamics differences between the Yaris and the Bonanza, however, I tend to agree with the others and expect the benefit of washing the Yaris to be imperceptible.

Along with the upcoming summer Olympics, I shaved my entire body and wear one of those swimmers caps and shaved my commute time by .0001 sec!!! I keep sliding off the seat tho- and this thong is incredibly uncomfortable on my long commute…

You should wash it when you can’t stand how bad it looks. A crud free cruiser is nice to look at but you won’t notice any less fuel mileage due to a filmy buildup. Wax it to protect the paint if it needs wax but the Summertime trip should be free of any trivial discussion about better gas mileage. Check your oil now and then. People argue about which is better; checking the oil hot or cold. Whenever you can. I like the idea of checking it before the car starts in the morning, but it’s convenient to check it when you fuel up. Never is a bad idea.

As to energy consumption I would think the miniscule amount of energy used in providing water pressure would more than offset any energy saved by washing a vehicle.

You’ll use more gas making one trip to the car wash than what you’ll save in a lifetime of washings.
The best thing you can do is check the tire pressure every other week and possibly add a pound or two to help things along.

Unlike power steering fluid, oil temperature (hot or cold) is not relevant, per se, but the engine does need to have been off for a minimum 5 minutes to allow oil to settle in the pan. Otherwise you risk overfilling due to a falsely low measurement.

I’ll leave it to others to explain how too much oil can cause engine damage.

If you can measure the road dirt you wash off in pounds, it might work.