87 535is mpg
I am a new member as of today, but I have a lot of experience with mpg and many other things in the '87 535is 5spd, chipped.
I purchased my ride in 1999 with 65,371 miles and a bad cam for $4300.
After bringing everything back to spec and installing a Bavarian chip, the original engine got 21 to 24 mpg winter and 24 to 28 mpg summer, year after year. If I high miled it, a lot of coasting, it would easily reach 28mpg in summer, by my manual calculation. I find my rally computer is fairly accurate as well.
The gentleman from Canada must be talking Imperial gallons. 30/40 mpg? Not possible in US gallons in this car.
Sadly, my original engine went south, I believe due to a mechanic's failure, back when, to blow the oil out of the head bolt holes when replacing the head. Probably the same guy who crushed the cam oiling tube putting the valve cover back on and launched half the cam, long before I bought this ride. We found multiple hydrofracs around multiple head bolt holes in the block. Naturally, I started getting oil in my coolant a few years down the road. It took time to discover, because it was always oil to water and not the other way around, and just a little bit. It got worse over time. I finally admitted to myself that the coolant was getting too funky and I would have to treat the problem.
My mechanic could not find an '87 3.4 liter, so he grafted a '90 3.4 liter bottom end to my original top end. I got the bigger intake manifold and exhaust ports of the '90 engine and retained the fuel/air management of the '87. The '90 top end and air intake would not fit under the hood. There were motor mount mods involved as well. Other than that, everything pretty much fit right together including the updated original air conditioning system, original alternator and steering pump.
Sadly, the '90/'87 hybrid engine uses a bit more fuel. Magically, the older, '87 fuel/air management system is happy to deliver all the gas and air the freer breathing '90 bottom end desires. I have much more power, possibly as much or more than the '90 engine originally delivered, which was 26 more hp than the '87 E28 plant. 208 hp for the former and 182 hp for the latter. You see, the chip, matched to the '87 top end and computer, is still in place. All I know for sure is that my mechanic is very proud of his work and loves to drive this car and he has an M5. I call it scary fast.
I am currently getting 18.5 to 21 mpg in winter and 22 to 24 mpg in summer. I used to boast of my mpg, but now, no can do. Whadyawant ? It's a high performance touring sedan with four doors, a big trunk and a nice back seat. There is definitely a payoff in the improved torque and accelleration.
My original owner's manual says that I will damage this engine if I don't use premium fuel. I use it. I also clean out the engine regularly with a high quality top end cleaner, These engines are prone to getting fouled. They are sensitive to water, so keep after the dry gas during big day/night temperature and humidity changes in fall and spring. It must rain in that gas tank. Keep the fouling down and the mpg goes up. Try a valve adjustment per the manual's reccommended interval. That helps a lot.
My owner's manual also assures me that this car, in original dressing, will do 135 mph in fifth gear. It's right in the manual. I love that.
I currently have a serious problem with my 535is which I will discuss in a new post which I will entitle: "Solutions for repair of rear subframe bushing mount points for the '87 E28?". I and my experienced mechanic will be looking for any help we can get.
Regards to all,