Hypermiling a BMW 750iL V12

Discussion in 'BMW' started by Ptero, Oct 5, 2009.

  1. Ptero

    Ptero Hydrogen Nut, Battery Skeptic


    I bought an old 1990 BMW V12 for $1500 from a low-rider who wasn't a mechanic. These things are like the space shuttle. Forget about taking it to the dealer. It's either do the work yourself or sell it to some idiot and run.

    The guy told me it passed the California smog test and he'd get me the paperwork, but as soon as the money changed hands he ran. He must have thought I was an idiot.

    I drove the car home from the DMV and parked it. It came without a maintenance history which meant I was taking a risk, that I might have to strip it to get my money back out of it. But there was an off-chance I had found a gem.

    The car was really straight. Not a dent in the underside. Not a speck of rust. I was convienced it had been garaged most of its life. There was a hint of cigar smoke. Maybe it had been sold at an estate sale.

    Strangest of all, almost everything worked. No error warnings on the computer. No dead pixels on either the dash or computer pixel displays. The all-leather power seats worked. Not a rip on the upholstery or dash.


    I started it up and balanced a nickel on the manifold cover. It stayed upright while the engine purred.

    Then I smelled gas and saw a big pool of premium spreading out from under the car. I shut it off quick. A tired hose to one of the twin fuel filters had ruptured. Scary. Easy to fix, though.

    There was a receipt for a full set of big Sumitomos in the glove box, but the wheels were fitted with big fat new Dunlops and there was a new Sumitomo spare in the trunk. The outside edge of the front passenger side tire had worn down to the steel mesh. Sure enough, the toe was cocked to the right. I eyeballed it back to true and took it out for a test run. Sure enough, it started shaking violently as I approached 50. Characteristic of 20-year old Beamers with worn suspensions. I had expected it.

    The lowrider guy had told me he had driven the car to San Francisco and back - about 800 miles. That would have done in the Sumitomos. Then he probably put on the Dunlops and drove it around town and finally took it to the BMW dealer. They would have offered to replace the front suspension for around $2800. Then he sold it to me.

    There's an outfit that advertises on eBay that sells full front/rear kits with the beefy aluminum lower arms for about $350, so I got one and installed it in the garage, along with air filters, fuel filters, synthetic 10-40 and filter. I was waiting on a delivery of Pentosyn for the power steering/hydraulic suspension when I had to leave for Chicago in the Smart Car to get the Shandong Pioneer, so the BMW got put on hold.

    I've always wanted one of these 5-liter monsters. People tend to think they're gas hogs, and they are if you put your foot into them, but virtually no one who is not familiar with them realizes that they turn over at half the speed of a V8 or a V6 or any straight-line engine. It's all torque, baby. Smooth, smooth torque. You can cruise in the slow lane at 1200 rpm, or pass a truck on the two-lane at 1500 rpm without dropping out of overdrive (5th).

    It's got a set of cats. That's it. No smog control other than the cats and O2 sensors. No distributor, either. It uses a crank sensor. I took it to the Smog Check Station, expecting the worst from its 133,000 miles. But that odometer reading is deceptive. In terms of engine revolutions, it's only turned over half as much as a V8 would to garner that kind of mileage. And sure enough, the tech came back with an emissions score that shocked me. At 2500 rpm, the hydrocarbon emissions were 49 out of an allowable 140 ppm.

    When I returned from Chicago, I took it for a 100-mile romp on a hot day. A few days later, I went on a 400-mile overnight trip. On the return leg, I decided to try driving for mpg. It has a wonderful meter on the dash that I assume is a glorified vacuum gauge. At speeds above 20 mph, it indicates an mpg range between 0 and 50. Sure enough, I could peg 50 on the downhill sections.

    Overdrive engages at 60, then you can back down to the low 50s, keeping a feather touch to prevent it from dropping down into 4th. It's a heavy car so it really sucks gas going uphill. I seemed to do a little better building speed on dips and letting the momentum assist on the uphill sections. On the flats, I could maintain 24-26 mpg, but my list of errands brought it down to 22 mpg or so. Better than a lot of SUVs but... SUVs suck.

    I tend to compare it to the Smart Car, a sensible vehicle. Nine fewer pistons. A peppy engine smaller by 4004 cc and an amazing 3700 pounds lighter. That said, the ride of the BMW is nothing short of awesome. It doesn't seem to care how fast you go. It's limited at 155 mph, which is 35 mph faster than you can fall, and, I've been told, is capable of 185 mph without the limiter.

    Now, that's a car. Or is it? Perhaps it's more like an airplane with 16-inch wheels. It cost $70 to go 400 miles. The Smart Car would have taken me to Denver for that.
    Last edited: May 10, 2010
  2. msirach

    msirach Well-Known Member

    Thanks Ptero! I wasn't familiar with this model. The engine looks like it's really tucked in. How many psi did you have the rubber on the landing gear?:D

    Any info on the Shandong yet?
  3. tjts1

    tjts1 Banned

    Very cool. Enjoy the ride. If you ever need parts, hit up your local JY. Ive seen more than few of of these V12s over the years, sometimes 2 in the same yard. I even saw an E38 750i last time. I'm at the other end of the spectrum with my 91 318i.
  4. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Ptero:

    ___Once you have gotten used to that BMW, maybe your next car will be a BMW with a lot lower impact and similar performance ;)

    A modern Day BMW :)

    ___Good Luck

  5. brick

    brick Answers to "that guy."

    Well, at least the benefit of buying a 20 year old car is that you can have your jollies without expending all of the energy that it takes to crank out a new one. But, $70 for 400mi...even at Cali fuel prices you're talking 17mpg tops. That thing had better drive like butter...dipped in chocolate...covered in silk...delivered on a pillow by some sort of forest nymph...I'm enjoying myself but I think the point is made ;) .
  6. Ptero

    Ptero Hydrogen Nut, Battery Skeptic

    Yeah, but that's why I thought it would be fun to see what I could do to get better mpg out of it. Also, the 17 mpg reflects a lot of city driving. In its stock form, the car does not do well below 60 mph because that's where the overdrive kicks in. I'm going to change that. And I have a lot of cylinders I could cut fuel to.

    I guess you'd have to have riden in a BMW V12 LH7 to feel the way I do.

    It's not the cars, it's the fuel.


    It's essentially the same engine. I want some hands-on.

    Last edited: Oct 6, 2009
  7. Ptero

    Ptero Hydrogen Nut, Battery Skeptic

    The terrible truth is this.

    I paid $1500 for the old BMW V12. Say it gets 17 mpg. Gas is $3.25/gal.
    I drive the car for 10 years and average 50 miles per day.
    $1500 + (365 days x 10 years x 3 gal x $3.25) = $37,087.00
    After 10 years I haul it to the dump.

    I take your advice and work to get a new diesel BMW.

    I drive the smart car to work for 5 years, saving $12,000/yr.
    I use 1 gal/day to get to work and back. Gas is $3.25. The BMW is $60,000 cash.
    I drive the BMW 50 miles per day for 5 years then sell it for $34,800.
    It gets 50 mpg, same as I get in the smart.
    (365 days x 5 years x 1 gal/day x $3.25) + $60,000 + (365 x 5 x 1 x 3.25) - $34,800 = $5,931.25 + $60,000 + $5,931.25 - $37,000 = $37,062.50

    This is why expensive high-mileage cars are a niche market.
  8. brick

    brick Answers to "that guy."

    Not really. Cutting fuel to a cylinder leaves you with an air compressor that delivers no useful work. That both saps energy from the working cylinders and screws up O2 sensor readings which will cause the other cylinders to run hella rich. Just give her a good tune-up and you'll come out ahead.

    (Engines with cylinder deactivation both cut the fuel and seal the valves to each dead cylinder. That cylinder becomes an air spring, with the only major losses being the friction from the rings against the cylinder.)
  9. Ptero

    Ptero Hydrogen Nut, Battery Skeptic

  10. nervousmini

    nervousmini Well-Known Member

    Congrats on your new ride.

    Yes, the E32 750il is a bit like the space shuttle and the cost to maintain one may make you wish you had considered buying the shuttle instead. I would not automatically dismiss the dealers, although you may see the mechanics running away when you pull in. :)

    Please inspect and replace all rubber fuel lines on the car. You will now be waiting for the next weak link in the fuel supply line to fail - and it will (I've seen it), better to replace them all.

    Suspension rebuilds on a 20 year old BMW is to be expected - and costly, almost everything that has a joint or bushing probably needs to be replaced. Be warned - aftermarket suspension parts, especially from unknown manufacturers, are almost always not worth the money or effort to install. The quality and materials are far below what I would even expect from an autozone/pep boys equivilant. If you really like the car and intend on keeping it, please consider doing it right the first time. If you want to avoid BMW prices there are many companies that can supply good quality parts www.bavauto.com is one such company.

    The M70/M72 engine series is actually 2 6 cylinder M30 engines sharing a engine block and crankshaft - with many of the parts shared with the 6 cylinder. It doesn't have a distributor but it does have 2 sets of distributor caps, rotors, ignition wires, and 2 engine control units.

    The gauge on the dash does display real time MPG and is not based on vacuum. It is actually pretty accurate.

    The ZF 4HP24 transmission is adaptive and if you continue to work at getting the trans to shift early, it will lower the thresholds and you will see "overdrive" faster. This is a 4 speed with overdrive unit, be advised that this trans commonly fails over 100,000 miles and is fairly expensive to replace. I definately do NOT advise letting just anyone perform repairs on this unit.

    I can neither confirm nor deny your reported top speed with speed limiter removed....:D
  11. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Nervous mini:

    ___It sounds as if you have become quite familiar with this vehicle as its owner(s) visit your shop frequently

    ___Good Luck and thanks for the info as always.

  12. nervousmini

    nervousmini Well-Known Member

    All too familiar, Wayne.

    I run when I see one of these too ;)
  13. SentraSE-R

    SentraSE-R Pishtaco

    A friend of mine owns the same car. He bought it about 10 yrs ago for $11K. Nice luxurious ride, for sure. Very expensive to repair and own. Something went wrong in the driver's power seat. $1200 to repair. Getting a mechanic to make that $11K car run = $8K. I think I'd rather own a sailboat.
  14. nervousmini

    nervousmini Well-Known Member

    I really shouldn't knock them that much. They are fabulous cars to drive, I would easily compare a 20 year old 7 series to almost any newer car for driving abilities and comfort - even the styling has aged well. But as Darrell said they can be incredibly expensive to own. The $1200 seat repair sounds like it needed a set of drive cables - Not a fun.
  15. philmcneal

    philmcneal Has it been 10 years? Wow

    wow bmw v12 you lucky son of a gun, please give us posted on your ride its awesome! what's the 0-60 time rofl if it can pull 25 mpg DROOL!
  16. Taliesin

    Taliesin Well-Known Member

    A boat might be worse:

  17. nervousmini

    nervousmini Well-Known Member

    Break My Wallet
    Bring My Wallet
    Bring Money With

    and the M cars are a multiplier

    regular repair Money * 3 = M3
    regular repair Money * 5 = M5
    regular repair Money * 6 = M6
  18. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

  19. Ptero

    Ptero Hydrogen Nut, Battery Skeptic

    You guys are pretty funny. I am a mechanic. I installed a new quality 15-part front suspension with aluminum arms and rear dogbones for $350. Peanuts. A BMW mechanic will never touch this car. I love this car. I got 27 mpg on the level highway yesterday just using a light foot. But I didn't fix it up just for hypermiling.

  20. Ptero

    Ptero Hydrogen Nut, Battery Skeptic

    Cresting Walker Pass on the southern Sierra range in California during a 185 mile mileage test.
    At the 80-mile mark at the 395/14 Hwy Junction, the computer indicated 26.7 MPG.
    The 1992 BMW 750iL V12 is entirely stock with new BMW-specified Michelin tires at recommended pressure.
    It slips into overdrive at 62 MPH and drops out around 55 MPH.

    Computer read-out at 185 miles, Bakersfield city limit.
    Last edited: May 10, 2010

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