08 GT weirdness

[m5pa]

Of course, since it's nearly paid off, our 2008 Mazda 5 has had some odd things happen recently.

My last two trips have been 90% highway. The first one with the air con off mostly, returned nearly 29 mpg at a steady 80mph (cruise of course) and light traffic. The last trip, with more air con use but the same conditions, saw only 20 mpg! Now, I suspect the tank might not have been allowed to fill completely, but that might not have been the case.

Last night, coming through some heavy rain, I was braking to a stop when the Brake warning came on, as did the EPAS (electric power steering) warning light. Car never stalled out or bogged down that I could tell, but it was odd. Simple explanation, the accessory belt got wet and began to slip. No check engine light or anything.

The optimist in me wants to believe the simple explanations ( tank not allowed to fill all the way, belt got too wet). The pessimist says that I've got some kind of electrical thing going on. Anyone have an suggestions? I haven't noticed anything unusual otherwise in the way it drives. Just clicked over 39k miles last night.

 

[thaxman]

My last two trips have been 90% highway. The first one with the air con off mostly, returned nearly 29 mpg at a steady 80mph (cruise of course) and light traffic. The last trip, with more air con use but the same conditions, saw only 20 mpg! Now, I suspect the tank might not have been allowed to fill completely, but that might not have been the case.

AC is a major drain on these 3600 lb 157hp 4-banger cars. A 30% drop seems to be out of the expected range though. Unless the trips were back-to-back and fillups were at the same stations, I would speculate part of this is from formula differences in the gasoline. That can account for 10-15% right there. Add AC, atmospheric differences, like headwinds or even barometric changes, and one can see perhaps another 5%. It is entirely possible that all conditions were conspiring against you the 2nd time.

Last night, coming through some heavy rain, I was braking to a stop when the Brake warning came on, as did the EPAS (electric power steering) warning light. Car never stalled out or bogged down that I could tell, but it was odd. Simple explanation, the accessory belt got wet and began to slip. No check engine light or anything.

My car has done funny things when braking in the wet. I still have the original off-the-boat 2006 software, and between the 2 of those, if my car was going to blow up, it would have by now. I think the dashboard warnings could be moisture/humidity related, but I don't worry too much about it on my car. As soon as the weather changes, everything is fine.

The optimist in me wants to believe the simple explanations ( tank not allowed to fill all the way, belt got too wet). The pessimist says that I've got some kind of electrical thing going on. Anyone have an suggestions? I haven't noticed anything unusual otherwise in the way it drives. Just clicked over 39k miles last night.

 

[Robotazky]

The brake warning lights came on in my '09 years ago in a heavy rain on the interstate when I hydroplaned.

I wouldn't worry about it at all.

As far as the mileage issue goes, I have posted dozens of times about the inability to calculate mileage properly because of the tank not filling to the same level each time. I've seen 34 mpg on a drive that has seen 21 mpg at other times.

I wouldn't worry about it at all.