"Okay so the 540i is somewhat of a contained monster wrapped in a sedan.
Let me start off by saying if you have under 4k or less and find a 540i that might need some work or none if you're lucky. Buy it immediately You will NOT be disapointed in any way. Due to its low price its hard to beat the ultimate driving machine or compare an all aluminum DOHC V8 to something else thats about 4k probably like a chevy Cavalier...
Being my first car and rebuilding engines at a young age. I soon realized that maintenance away from the dealership is key (especially for high end-high mileage vehicles). The 4.4 in this car will blow your mind when compared to any mustang or camaro produced up until about 2009. I've had my share of racing in this 540i and no mustang, camaro,wrx,240sx etc.. comes close to beating the acceleration. Of this 4500lb car. with 310ft lbs of tq in 1998 is pretty fantastic. But the car has some serious flaws- The cooling system is the most common and worst e39 problem, the radiator will eventually clog/or explode(no joke) every 70k unless you upgrade away from OEM fluids. Cant stress enough use every OEM fluid you can obtain. @ 177,000 my power steering high pressure line busted and empties the reservoir in about a day. and is impossible to fix w/o puliing the engine. but granted is very very rare in an e39. Also when i purchased the car the brake booster and master cylinder were seized up and rusted, After replacement no issues regarding brakes in 15k miles. and the cup holders are seriously the worst ever designed for a vehicle. overall any basic maintenance such as oil, Spark plugs and gaskets. this car is extremely easy to work on and relatively cheap in terms of the use of Xbay and pelican parts. Perks of this car are stock rs-gt or style 19 BBS wheels if you're lucky. and if you do some minimal exhaust work it will put any muscle car to shame."
"I have had my 98 540i Sport for several years. My car has the 6 speed manual transmission and Dinan Stage 1 package. It only has 129,333 miles, so really low for a 18 year old luxury sedan. In a nut shell, it has been one of the best cars I have ever owned. I have owned over 40 cars in the last 16 years so keeping one for 2+ years is unusual for me. You are getting a lot of car for your money. My biggest complaint is its low resale value. My car was around $55,000 new and it books $4400! really!!!! If you find a nice one that has been taken care, jump on it. Dollar for dollar you can't beat it. Reliable, Fast, Fun, Luxurious, ect. I was considering selling it to buy another Jeep Wrangler but I have a hard time selling it for pennies on the dollar when I put $4500 into a clutch, flywheel, smoked head lights, Z-rated tires and other preventative maintenance in the last year. It books less than my last years maintenance and I don't agree. This car should be valued closer to double what KBB says in my opinion. A lot of car for the money...."
"I've driven and owned this car from 50,000 miles. The only problem I've ever had is an overheating problem a couple times. This is a stylish, incredible handling automobile that seams to never go out of style. I've LOVED this car!!! I've owned Mrecedes, Porsche's ( 5) Buick, Olds, chevy, ...this car is the mac DADDY!!! Bomb Diggity!"