You might look through craigslist or buy here pay here dealerships and notice you can find nice looking n54’s for a low price. But be warned there is an 85% chance you will be buying a dud of a car. The main reason why is the maintenance schedule was not followed by the prior owner. When this occurs it causes other issues to occur, such as the 335Xi I was working on.
If the prior owner changed the oil filter and cooler gasket, the entire cooling system and components could have been saved. This encompassed oil mixing into the coolant, and oil starts to leak all over the engine bay. The first thing it hits is your alternator, accessory belt, Pulleys, and tensioner. The life of those items has been shortened or deteriorated. Also With oil in your coolant there goes your water pump and thermostat, and hours of flushing out the whole engine.
So with the oil mixing with the coolant in other platforms that’s a red flag stating the head-gasket is blown and other big problems possibly. On the e9x series, a blown head gasket is not likely at all. Most e9x series you see for sale on Craigslist and such that state head-gasket it’s typically just a 15 dollar part that needs changing, and then a bunch of dollars to replace all the damaged parts, but as long as the body and interior is clean the car can come back from the brink of scrap yard to on the road again.
After all this neglect the owner will realize they have a repair bill in the thousands. They then trade the car in, and when the dealer actually looks at the car, they push it on to the auction where another dealer pays for it and usually ends up at a buy here pay here type of establishment. They put it through a good cleaning and get it to a point where a test drive is feasible. You then see the ad and think what a steal of a price! Run like the wind these cars aren’t for the everyday consumer. You will need to invest a good amount of money to have it in running order.
My suggestion is if you see an n54 powered car such as a BMW 125i, 335i, 535i, or x35i priced to low. Please exercise diligence and get a PPI at an indy shop that is familiar with modified n54’s. I have seen BMW dealerships that have given good ratings on cars that definitely didn’t deserve it. Also if your able to work on these cars, this is somewhat of a come up. In which you can haggle a lower price and put in the work and fix it and turn a profit.