24mpg on my 325i

[///M42 sport]

This is about how much I get on the highway. Is this normal? Think I should replace my o2 sensor?

[PeaveyBassist]

If I drive 90-95mph on the highway I get about 24mpg. If I drive conservatively at the 70mph speed limit I can get as high as 27mpg. 24mpg seems relatively ok to me.

Will

[Jon '92 325ic]

Depends on your rear diff ratio. for an m20 engine with a 4.10 rear diff (open or lsd), 24 mpg highway would be on the high end. I believe that's what they were quoted as getting when brand new way back then.

When I had an open 4.10 I was getting 22 - 24 mpg highway. I put in a 3.91 a while ago and now I'm getting 24 - 27 mpg highway.

I don't think your 02 sensor needs replacing. When mine needed to be replaced (back when I had the 4.10) I was getting like 15 - 17 mpg. My mileage was so bad that it was pretty obvious something was wrong.

[Jarvis]

Re: 24mpg on my 325i

This is about how much I get on the highway. Is this normal? Think I should replace my o2 sensor?

Well if you drive an M42 car like your name suggests, and you drive at normal freeway speeds (60-80mpg), then yes something could be off. M42s should get 30mpg+ 65-75 mph easily.

[///M42 sport]

ah thanks. I have a open diff., not sure what ratio it is though. Its also an auto so I guess the mpg is about right then.

[PeaveyBassist]

m20b25 auto tranny = stock 4.10 diff
m20b25 manual tranny = stock 3.73 diff

Will

[RCWells]

Since I went to a MarkD 93octane chip, I get 20mpg, no matter how lightly my right foot is. That sux. I have been considering going back to a stock ECU/chip and running 87octane to save dough.

[Jon '92 325ic]

M42 - type of diff (open or lsd) doesn't affect mileage. I'd guess you've got an open 4.10, so 24 mph highway is pretty darn good.

RC Wells - 20 mph highway or overall? I'd heard that Mark D chips, like Dinan chips, don't decrease your mpg. The figures I mentioned above for my highway mileage are with a Dinan chip.

[RCWells]

With the JC chip I had before, I was getting around 24mpg. Now with the MarkD, I get about 20(rounding up). That is just city driving, but even on the highway, it's not much better, maybe a couple more mpg. It's just been not so good since the change, but the power increase was very noticeable. It's just that gas has gone up so much, and having to run 93octane is expensive.

[UNHCLL]

Even with the stock chip you cant run 87 RCWells.
You can get away with 89... no less.


I get ~30mpg on the highway in my 325i w/ a manual tranny and 3.73 LSD @ 70mph. I've done the real math, not just going off the OBC. OBC tells me 33mpg.

[Jarvis]

Even with the stock chip you cant run 87

Um, what?

Aftermarket exhaust increased my gas mileage before by a large amount.
In my old 87 325is I got 23-24mpg on the highway (constant 70mph) until I replaced the stock exhaust with a Stromung, and then started getting ~30mpg (same constant 70mph). On one 300 mile trip from eastern MA to upstate NY I actually got a little over 31 mpg, that was with a few hundred extra pounds of junk in my car because I was moving. I can be very OCD about gas mileage figures and would always do the math when I filled up. The OBC was never off by more than 1-1.5 mpg. It was usually off by no more than .5mpg.

[RCWells]

Even with the stock chip you cant run 87 RCWells.
You can get away with 89... no less.


I get ~30mpg on the highway in my 325i w/ a manual tranny and 3.73 LSD @ 70mph. I've done the real math, not just going off the OBC. OBC tells me 33mpg.

Both I have owned had "chips" in them so I have run premium gas from the start so I didn't know that. But, that would still be cheaper than 93.

[UNHCLL]

Even with the stock chip you cant run 87

Um, what?

Yup, you'll ping like a mofo on 87 in a 325i/is. You can safely run 89... no less.


You can do 87 in an economy E30. 325/318i/325e/etc.


I forgot, my car has a stright through muffler... was going to replace it with a stock one to quiet it down, but we'll see.

[Jarvis]

I forgot, my car has a stright through muffler... was going to replace it with a stock one to quiet it down, but we'll see.

Putting up with the noise/losing a little low end power is worth the considerable increase in gas mileage with a high-flow exhaust.