Automotive depreciation is kind of like Robin Hood: it makes models that would regularly be available to only the rich, accessible to those with even the most laughable of bank account balances. But what good is it if the car has notoriously expensive mechanical issues? Don't worry, I got your back.

The 2002-2008 BMW 7-series was controversial to roughly the same degree that Beyonce is underrated. It had styling made by the love-him-or-hate-him Chris Bangle, and was the first car to come equipped with BMW's proprietary iDrive system, which had the user-friendliness of the Large Hadron Collider. Its long-wheelbase, fully loaded models still had technology that the current S-Class didn't have, like electric rear side window shades, six-speed automatic transmission, electronic parking brake, and an infinitely variable intake manifold. This meant that the car had some serious kit to go along with its awesome, near six-figure original price tag. But there was huge problem, and its name was BMW.

During the early 2000s, BMW was regularly having its lunch eaten by the , and in order to one-up the rival German automaker, they employed longer engine oil change intervals, called Condition Based Servicing, or CBS. What this meant is that new BMWs needed their oil changed once every 15,000 miles as a minimum, in an attempt to get people interested in their new line of Bangle-butts. Just as time heals all wounds, it also exposes bullshit. 15,000 miles, as it turns out, was way too long of an interval for the 4.4 and 4.8 liter N62 V8s in the 745/750i.

What this mistake did over time was harden the engine's oil seals so that they became brittle and would leak, allowing oil where it shouldn't be – in the intake manifold and in some cases, the combustion chamber – which decreased performance and gave a noticeable plume of whitish blue smoke when running and idling. While oil seals can be potentially expensive on a regular car, they can be downright financially suicidal on a BMW as complex as this. If the problem is valve guide seals, a competent BMW dealership would likely charge between $4500 to $8,000 in labor alone.

For that reason, you can find decent used examples for well under five figures today. Seriously, .

The Fix

If your new-to-you 7-series starts becoming a chain smoker, you have a few options and likely possible causes:

The CCV, also known as the PCV valve, allows a vacuum from the intake manifold into the crankcase, relieving pressure and saving oil seals from that excess pressure. When these parts fail, they can allow oil to seep into the intake manifold and into the combustion chamber, causing the telltate bluish-white smoke. The parts required are around $50, and the whole thing can be completed with hand tools in short order. Here's the entire procedure from start to finish:

This is another fix that involves a cheap part, but the labor is the killer. The valve guide is an integral oil seal between the combustion chamber and the cylinder head. If the above CCV fix still doesn't change your car's smoking habit, the valve guide seals may be the likely culprit. To change this part traditionally, you would have to remove both cylinder heads, which means a complete disassembly of the front of the engine, intake manifold, exhaust manifolds, and timing equipment, as well as all accessories and cooling components. This is where that near-five-figure budget for labor comes in.

By the powers of the free market, a forward-thinking company called All German Auto has developed a tool that allows you to keep your engine largely intact, cutting install time and costs by orders of magnitude. , and while it is expensive, it's absolutely everything you'll need to complete this job, other than the actual valve guide seals, which are about $50. You can always sell the tool when you're done with it, but with the price of a traditional repair method, one use of this tool would've already paid for itself. Although a good independent shop should routinely charge around $600 for a job of this size, it's something you can definitely do yourself over the course of a long weekend. Here's the entire procedure:

While the oil burning issue isn't the only common issue this car has, it is the one that most people consider the most daunting, and one of the biggest reasons why this car has depreciated to the point where nearly anyone can afford to buy it. It's a crazy value, and if taken care of with regular 5,000 - 7,000 mile oil change intervals, it can last a long, long while. .

For more little-known fixes to well-known problems, check these out:

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