This car was sent to me from another shop because they were too busy to get to it, and the lady needed it repaired ASAP.
Symptoms were engine oil warning lamp would flicker when engine was first started cold. After warming up the oil lamp stayed on and the engine had a loud rattling noise. The first shop replaced the engine oil filter, but not the oil as it looked fairly clean. This made no difference. They were kind enough to put the old filter in a bag and sent it to me with the car.
When I cut the filter open I found no sign of metal or any engine wear. I was able to duplicate the symptoms. The engine sounded normal when cold, but as it warmed up it developed a rattle/ knock and the oil light stayed on.The rattle almost sounded like lifters, and was coming from the front of the engine. A visual inspection showed the engine oil lamp sender was leaking. I verifyed oil pressure with my WPS500 & pico scope. I like using the WPS for engine oil pressure as it shows exactly what the oil pressure is doing. I have found a couple restricted oil pickups this way.
Thinking the rattle could be a timing chain I also put cam and crank sensors up. As you can see, when cold there is 890 micro seconds between the cam & crank pulses and oil pressure is very good at 75 psi. After the engine warmed up there is now 1.71 milli seconds between the same two pulses and oil pressure is still good at 29 psi. This made me believe the timing chain tensioner had failed. When I replaced the tensioner and oil pressure sender all was back to normal. I forgot to save an after repair screen, but looked the same cold and hot , except oil pressure dropped to 30 psi.
We had told the customer before we started that she might be looking at replacing the engine. She was very very happy to find out what actually fixed it.