Smoking BMW 750li : Causes and the fix.

11 Jul Smoking BMW 750li : Causes and the fix.

Today we will look at a customer’s Smoking BMW 750li 2006 E65/E66 chassis.

This particular vehicle came into the shop to find out how to fix their Smoking BMW 750li that shot clouds of blue smoke from the tailpipe. When idling or taking off from a stop the smoke would cover billow out behind, and was also having high oil consumption. At Fluid MotorUnion, we know that owning a luxury vehicle with large plumes of smoke coming from the tailpipes is kind of counterproductive. The good news is that this customer chose to purchase a third party warranty when buying this car. The bad news is that this problem is all too common on the BMW N62B48 platform. We like to refer to these vehicles as “enthusiast cars” due to their groundbreaking features as well as their many high-cost repairs. This is one of those such repairs.

After checking for external oil leaks and performing a leak down and pressure tests to the cylinders, we moved on to test the crankcase oil separation system or the PCV system. After checking for tears in the crankcase vent valves, we came to the conclusion that the most likely culprit was the valve stem seals. Valve stem seals are meant to provide an oil barrier between the valve stems to the cylinders and the air intake and exhaust ports respectively. When the valve stem seals leak, the oil will enter the cylinders if the seals are leaking on the intake side of the exhaust manifold if the seals are leaking on the exhaust side. Bad seals on either side will result in burning oil, rapid carbon deposits on
engine internals, and, ultimately, large amounts of smoke coming from the tailpipes. In order to please the third-party warranty company, we were told to remove the cylinder heads to verify our diagnosis.

Once the heads were removed, we found the intake ports and pistons in good condition, while the exhaust ports were caked in burnt oil/exhaust. This showed us that the valve stem seals were leaking into the exhaust ports. Now, technically the cylinder heads do not need to be removed in order to complete this job. However, we chose to go this route for a few reasons. First, compressing the spring to remove and install the valve keeper is a very difficult task with the head out of the car on a bench, let alone on the engine with you leaning over the fender. The price of your sanity is never worth the extra time it takes to remove the head from the car. Next, having the cylinder head off gives you a chance to clean the affected ports and pistons while also being able to check the overall health of the engine. It would be a shame to go through all that work only to find out one or more of the cylinders had visible damage that could only have been detected with the head off. Lastly, if everything in the cylinders and valves checked out, replacing the head gasket will go a long way in extending the overall engine life.

While replacing the valve stem seals alone is a big job, there are other areas that can be maintained preventatively at no additional labor cost. We will get into one such job on the next blog post. Until then, if you are dealing with a Smoking BMW 750li, our Experienced BMW Mechanics can offer you the best repair suggestions no matter your situation. We are conveniently located in Naperville just a short drive from I88 in the Chicago Metropolitan suburbs.