03 Aug Gunk Yard
We were so excited about the other parts of today’s post that we completely forgot to include this! So let’s do that now.
This is an issue we’ve seen before, and while it is a shame to see, it can be avoided by — funny enough — breaking the rules. Starting with some of the later models of BMW, they’ve started recommending 15,000 mile intervals for oil changes. This can have a few unintended consequences when coupled with other factors, as we’ll explain below.
Basically, this 525i came into the shop with a check engine light. After diagnosing it as a camshaft limit fault, we took steps to reset the VANOS system, which is the recommended diagnostic step after discovering this issue. All our efforts didn’t work, though, so we set about taking off the valve cover to see what the issue was. When we did, we were met with this:
What you see surrounding the back of the VANOS unit (the extra piece past the cam gears and timing chain) is a sludge that consists of long-interval oil and several other things. Motor oil contains a good deal of dispersants, detergents and additive packages that aid in lubrication and longevity of both the oil and motor. As the oil ages and continues to experience heat cycling, it begins to break down. At the same time, fuel washdown also starts to affect the valvetrain; when you first start a car and the engine is cold, the ECU is dumping extra fuel into the mixture. To get rid of all the excess fuel being dumped into the car during the cold operation, it’s recommended that you drive the car for roughly 12 miles or 25 minutes. Otherwise, that washed down fuel can escape past the piston rings and into the oil, spreading it basically anywhere the oil goes. Couple both the oil and fuel with moisture from the engine running, and you get the nasty gunk you see here. Here’s a quick clean of the VANOS unit before we dug deeper to fix the issue:
The VANOS unit connects to the front of the camshafts, and is actuated by a smooth-bore piston. As time goes on, this gunky buildup can accumulate in the VANOS unit, causing premature wear on the seals and the eventual failure of the VANOS unit itself. Keeping your motor’s oil clean, and trying your best to eliminate fuel washdown are two important steps in keeping vital pieces of your motor in tip-top shape. From our experiences with a variety of full synthetic motor oils, we recommend never going over ~7,000 miles between oil changes, even if it’s recommended to be a longer interval. Skimping on oil changes now will end up costing you in the long run; so far, we’ve had to remove the valve cover and the VANOS unit, clean the VANOS and replace its seals, then reassemble and re-time the motor. Obviously this isn’t a two hour job — it’s costly, which is why we try our best to keep customers aware of these sorts of issues. And we’re in the midst of that process with the 525i right now:
Motors are becoming increasingly complex, and in order to comply with ever-stricter emissions standards, motors are also running hotter than they used to. Because of that, washdown fuel and oil is more likely to break up and begin accumulating in bad corners of your valvetrain. This increased complexity not only contributes to the degradation of the oil, but also the marked increase in costs to repair this sort of problem. It can be avoided with sped up oil change intervals and an efficient maintenance schedule. Have a great weekend!
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