Sub par MPG in 325e

[ATL_E30]

Hey Everyone,

Little background I have a 1987 325is that gets about 350-400mpg. I'm a commuter in Atlanta so lots of traffic. I found a 1988 325e that I was hoping would get better gas mileage, but it seems the opposite happened. I'm consistently getting around 250-275mpg in the 325e which is significantly lower than what I thought I'd be getting.

Reaching out to some of you M20 experts to see where I should start looking?

Edit** Both cars running on premium gas

Cheers!

[Elysian]

Why premium in the eta?

[325e '87]

I’m not an expert, just offering my opinion. I believe the motronic uses coolant temperature, air flow meter, and the O2 sensor to refine the fuel mixture. If I were having a rich running engine I would replace the coolant temp sensor and O2 sensor.

Do both cars take about 12 gallons to fill up? We have an 87 eta and it usually gets 25mpg, which is lower than it should but it runs good. My 89 i gets about the same, 25-27.

[ATL_E30]

Why premium in the eta?

Scientific Method, Testing with an experiment on both cars aka have consistency between them

I’m not an expert, just offering my opinion. I believe the motronic uses coolant temperature, air flow meter, and the O2 sensor to refine the fuel mixture. If I were having a rich running engine I would replace the coolant temp sensor and O2 sensor.

Do both cars take about 12 gallons to fill up? We have an 87 eta and it usually gets 25mpg, which is lower than it should but it runs good. My 89 i gets about the same, 25-27.

Yep, both take about 12-13 gallons to fill from empty. I ran the ETA dry the other day and it filled up with a little over 13 gallons.

I've take a look at replacing these sensors and see if there's a change.

[Elysian]

Scientific Method, Testing with an experiment on both cars aka have consistency between them



Yep, both take about 12-13 gallons to fill from empty. I ran the ETA dry the other day and it filled up with a little over 13 gallons.

I've take a look at replacing these sensors and see if there's a change.

Manual says 87 in an eta, if I'm not mistaken. Not very scientific to run the wrong fuel in a car ;)

[ATL_E30]

Manual says 87 in an eta, if I'm not mistaken. Not very scientific to run the wrong fuel in a car ;)

Did you find this in the Bentley? Was just trying to be consistent with both cars

Also in the 325is I have noticed a 25-35mpg boost from running premium, car isnt chipped either so was just going with that logic.

[Bimmer_Baron]

The ETA uses a low impedance injection system, meaning the injectors have about 2-3 ohms of resistance, instead of 14-16 ohms of resistance compared to the 325i injectors.

A consequence of this is that the ETA injector solenoids go bad faster than the 325i solenoids.

If the injector solenoids are starting to go bad, the injectors could be activated and opening longer than they should be. Or, the injectors themselves could be totally fine, but could be full of gunk and need to be rebuilt.

That's the only ETA-specific thing I can think of that can be causing bad gas mileage, everything else is stuff that can happen to the 325i as well. Basically anything that plays a role in squirting fuel into the motor, lighting that fuel on fire, and doing science to measure the amount of air, fuel, and the exploded combination of the two is suspect.

[M-technik-3]

Have you factored in wear and tear. It's not brand new anymore it's 30+ years in age and parts that affect how the car runs. Winter blend is also a crappy fuel source, it has crap blended into it so your mileage drops about 10%.

[cunninglinguist]

1988 Supereta didn't get as good MPG, plus what everyone said.

[Kershaw]

325is getting 400 miles to the tank and 12 gallons to fill up? That's 33mpg and I'm calling bs. My eta, in it's best shape, got 30mpg, and that is fairly common for etas. You want better gas mileage out of an e30, you need to go down 2 cylinders.

A 325is will get 24.5mpg at best. Anything more than that and something is messed up, your odometer or tire size probably.

[jeffnhiscars]

Both regular and premium have exactly the same energy content. The difference is in anti knock additives which prevent pre-ignition (ie pinging) if the CR is over a certain threshold which a stock 2.5 isnt.

If you think mileage is improved its the placebo effect..."I paid more for it so it much be better". If your engine isnt knocking on regular, using premium is just burning $$. I know cause I did it for years :)

[superj]

30 in an eta and 25 is an I is normal. all my cars have been that way. I have no experience with a super e though I have owned about 12 or 13 e30s in general, maybe more.

I prefer the mileage of the eta. I used to drive a little over 300 m-f and the eta was great. all four of the cars in my driveway now are etas.