I changed my oil yesterday with 6 quarts of 10w40 Castrol Syntex after about 5,500 miles on same oil. 1995 BMW 525i with M50TU 6 cylinder 2.5-liter engine with about 163,000 miles

I had started to notice a light clicking before the change after a 20 second or so warm idle. The noise is slightly more pronounced the longer the idle. In addition, it kind of comes and goes. However when revved it disappears or I just may not hear it.. There is no change in clicking noise after the oil change.

I think it is just a sticky hydraulic lifter. Not much I can do. I have completed three Auto-rx treatments. Any thoughts?

Is the Syntec 10w/40 A3 rated? Not saying that is the problem, just asking a question. Have you ever tried GC? It's technically a thinner oil but it has been known to quiet an engine down.

Mike Miller of Tech Q&A in Roudel magazine claims that BMWs perfer thicker oils which is contrary to todays theme (thin is in). Maybe you could try M1 15w/50 - it'd flow plenty good in your climate and if your engine was wanting a thicker oil, that would fit the bill...

Just thinking out loud..

tried GC 0w30 and as i remmember it made for a noisier engine.

I May try thicker oil. I thought about using Castrol 5w50 next fill in teh spring.

Auto-Rx it. I'm in rinse phase on my BMW, a huge change.

He allready did that 3 times. I think Auto-rx is out on this one.

Injectors have been suggested as the problem.

Mine are original. I use mostly Chevron Supreme 93 octane fuel and used Redline Sl-1 (not sure of name)injector cleaner at the maintenance level. I have not used the redline for several thousand miles.

Did you change oil filter brands?

Get a wood stick on put it on the injectors, place your ear on the end of the stick and listen. Then put the stick on the valve covers and listen. You might be able to differentiate the noise. My old Cutlass had that problem and it turned out to be the injectors and they worked fine right up until I sold it at 205K. I would sure be hesitant putting a heavy oil in that engine this time of year.

Sticking lifters? Rare. A real sticking lifter causes rough running.
More like leaking lifters, or loose clearances elsewhere.

Thanks for teh reminder. You are correct. I used the wrong termnolgy. I have suspected the oil is leaking from lifters at idle and perhaps at speed.

What can i do? Would heavier oil help? Is there a problem with oil pressure/oil pump?

I wouldn't be in a hurry to go any thicker.
Even if it attenuates the noise!
There are all sorts of parts that click and make noise. Injectors can be pretty loud, and are often heard of as lifter noise. Cam chain or tensioners are another.
I'd keep digging until you are sure what is wrong. Maybe just one bad lifter is all that is wrong.

Thanks for the advice. I will continue to watch. No plans to jump on this issue too quickly. I have other issues on the car that seem to have higher priority at the moment. :) I need get some winter tires. Looks like we are going to have real "winter" here in central KY.

It could be an injector. Have you done a valve adjustment to the car? IIRC it is a maint item on BMW, at least that's what I read and was told about my son's car. Although not many members arw fans of MMO it has worked at freeing up junk in lifters, it might be worth a try for a 500 mile run.

Frank D

No valve adjustment on M50-series engines.

Injector or small exhaust leak at the head would be my first thoughts; lifter possible as well, though much less valve noise in M50 motors than earlier BMW engines. Remember that ethanol-blended fuels have lower lubricity, which may exacerbate injector noise.

Great comment. As afar as I know Chevron 93 soes not use ethanol.

I had been using lucas or redline fuel additives. They both offer UCL lubrication. Stopped using a few months ago. Think I will try the lucas as it is available nearby.