As long as I can remember, we’ve had a great relationship with other auto repair shops in the area. My father used to network with shops when I was growing up. We would always share know-how and tools.
When I took over the shop in 1990, I became a member of the Automotive Service Council of California. It’s an organization that encourages shops to communicate with one another and holds monthly meetings to discuss the ever-changing automotive field.
We recently received a call from one of those shops. It had a customer with a 2007 BMW 335i. The customer said the oil pressure light came on when the car was cold. After checking the engine oil level, the first thing the other shop did was remove the oil pressure switch and test the oil pressure. At idle, the engine oil pressure is supposed to be 21 pounds per square inch (psi); they were seeing 5 psi. As the car warms up and the RPMs increase, the oil pressure should read 58-87 psi. The other shop was testing only 30 psi.
When you open the oil filler cap and pour oil in, it flows to the oil pan (sump) at the bottom of the engine. Nearly all oil pumps sit at the bottom of the engine block. A timing chain/belt or the engine crankshaft drives the oil pump.
The oil pickup tube is bolted to the bottom of the oil pump. A funnel (strainer) sits at the bottom of the oil pickup tube. The funnel is covered with a screen or mesh (filter), so trash or debris is not pulled into the oil pump. The strainer sits approximately 4 inches from the bottom of the oil pan. Once the oil gets pulled into the oil pump, it is forced under pressure through the oil filter, then into the main oil galley, which is like a cardiovascular system, delivering oil under pressure from the bottom to the top of the engine. The oil goes to the crankshaft main bearings, crankshaft rod bearings, crankshaft end bearings, camshaft bearings, push rods, lifters and rocker arms. Once oil is done lubricating these parts, it returns to the oil pan to start all over.
The individual components that need to be lubricated must be in proper working condition. As the car ages, parts wear out and carbon can start to build up inside the engine. If those components are worn out or if there is too much carbon buildup, the oil system can lose oil pressure.
BMW’s 6-cylinder engines rarely have oil pressure problems with their oil pumps.
The other shop then checked the oil filter to make sure it was intact and working properly. The oil filter was intact, but what they noticed is that there was very little oil in the oil filter housing. The other shop then tried to manually add more oil in the oil filter housing to see if the oil pressure would come up, but it did not.
That’s when the shop called us. We explained that there is a cam ledge problem on these motors. The camshafts sit directly into the head. If the camshaft and where it sits in the head get worn out, the car can lose oil pressure. We also told the shop to pull the camshaft vanos control solenoids to check for slug or carbon buildup. If the cam control solenoids have carbon buildup, the oil galleys may be plugged. If those look good, pull the oil pan and check for debris in the oil pickup strainer.
A week later, the other shop told me that everything it checked on the outside looked good. Oil pan removals on this engine are costly, but the other shop ultimately had to remove the pan. With the oil pan off, the shop discovered in the oil pump strainer what looked like a shredded accessory belt. A call to the customer revealed that a month earlier, he had an accessory belt break on the road. A different shop had replaced the belt and the front crank seal.
Once the belt material clogged the oil pickup screen, the oil pump could not build pressure. The other shop cleaned all the belt material from the pick up and oil pan and, after reassembling the motor, it had 80 psi operation oil pressure.
This was one of the most interesting cases I’ve heard of in my career. It teaches us as a shop to ask as many questions as possible. It’s also a reminder to customers to tell us everything about your car. I’ve had a great relationship with this other shop and expect us to help each other for years to come.