Rain kills gas mileage.

[V8toilet]

There was a decent continuous driving rain today on my 70-mile commute home. I filled up just before I left and reset the computers ave mileage trip. Normally when I do this I can get the computers avg gas mileage to the 36-37 range for the first 140 miles. With this driving rain I was going slower and the engine seemed to struggle especially up hills more than usual. When I got home it was only reading just over 30 mpg and it was only 28-29 for most of the trip. I know rain creates more drag but man it really hurts gas mileage.

 

[SayNoToPistons]

Yes... Rolling resistance, drag, draw on the alternator from wipers, fans, lights, etc.

 

[Dr_Watson]

I would not imagine rain and wipers can hurt as much as 7 mpg. More than likely the wind, even a breeze in the nose will have an affect, especially as cruising speeds increase.

I have not seen any change in mpg when comparing dry and wet, only warm and cold and or windy and calm.

The ac drops the mpg, but not by much, although I run it in Eco mode, but have no idea what that means?

 

[MikeM.]

I would not imagine rain and wipers can hurt as much as 7 mpg. More than likely the wind, even a breeze in the nose will have an affect, especially as cruising speeds increase.

I have not seen any change in mpg when comparing dry and wet, only warm and cold and or windy and calm.

I agree that 7 mpg lower is a bigger hit than could be expected from rain alone. Wind is the most likely additional culprit. Rain can actually sometimes improve mpg over cool, dry conditions because the additional humidity can improve combustion efficiency slightly. But it can also lower mpg when it's raining hard enough to build up on the road surface. This is evidenced by the very obvious deceleration that is felt when a fast moving car is driven from pavement that is merely wet into standing water on the roadway. During very heavy rain the entire roadway has a film of standing water and the tires are continuously trying to push it out of the way. During extreme rain events, at high speed, any car can start to take on boat like characteristics. And I've never had a fast boat that sipped fuel! Best advice is to slow down in heavy rain (for mpg was well as safety). Tires designed to be good at water evacuation can help a lot (with mpg and safety).

The ac drops the mpg, but not by much, although I run it in Eco mode, but have no idea what that means?

Eco A/C mode must be unique to diesel or non-North American market, no mention of Eco mode in my manual. Have you checked your manual?

 

[Dr_Watson]

Have I checked the manual.....if I can be bothered hunting through pages of German I might!

 

[MikeM.]

Have I checked the manual.....if I can be bothered hunting through pages of German I might!

I checked my manual in an attempt to help. But your English seems very good. Perhaps there is a British manual on-line that could be downloaded for quick reference? The digital manuals are especially helpful because they can be quickly searched by keyword.

I don't know if this would work for you but I thought it was worth suggesting.

 

[Dr_Watson]

I'm British, Scottish! Living overseas, I have the us PDF, I need to check for a uk PDF, someone already asked in another thread, but I think dad of Jon will prob know what Eco ac is so I will just be lazy!

 

[ta240]

I find even a strong side-wind seems to negatively impact my mpg, I guess it must throw off the aerodynamics of the air flowing over the car. Or I'm just imagining it

 

[Latitude Adj.]

Could be too since you don't or shouldn't use the cruise control on wet roads that your speed wasn't as constant.

 

[madar]

Most likely from your defroster being on if you used it, cycles the A/C to keep the windows from fogging.

 

[MikeM.]

I'm British, Scottish! Living overseas, I have the us PDF, I need to check for a uk PDF, someone already asked in another thread, but I think dad of Jon will prob know what Eco ac is so I will just be lazy!

Here's a linky to UK Owner's Manual:http://api.viglink.com/api/click?format=go&key=75163e199044da94ec04c4b7a0d74a89&loc=http%3A%2F%2Fwww.mazdas247.com%2Fforum%2Fshowthread.php%3F123817748-How-many-Brits-Fancy-a-cuppa%2Fpage38&v=1&libId=c8d54f06-be10-458f-b4ac-00ac93164aea&out=http%3A%2F%2Fwww.mazda.md%2Fuserfiles%2Ffile%2Fcartea%2520de%2520explotare%2FText_PDF_(CX-5_8CF2-EE-12A_Edition1).pdf&ref=http%3A%2F%2Fwww.mazdas247.com%2Fforum%2Fforumdisplay.php%3F471-CX-5-Lounge-amp-Welcome-Area&title=How%20many%20Brits%3F%20Fancy%20a%20cuppa%3F%20-%20Page%2038&txt=%3Cu%3E%3Cb%3EEdition%201%20Users%20Manual%20UK%3C%2Fb%3E%3C%2Fu%3E&jsonp=vglnk_jsonp_13708189283238

 

[dad of jon]

I'm British, Scottish! Living overseas, I have the us PDF, I need to check for a uk PDF, someone already asked in another thread, but I think dad of Jon will prob know what Eco ac is so I will just be lazy!

flattery always welcome, but beer and chocolate even more so

It's the economy setting, for when it's not too hot outside but you still want chilled air. I only use full a/c when the car had been left with all windows closed in strong sunlight. Once it's cooled I switch over to a/c eco setting.

a few OP's from USA have mentioned how powerful the A/C is, with the weather we have in uk the eco a/c setting is fine for most occasions.