Low level "tock" sound

Have a 96 e36, it has about 80k on it and runs fantastic, pleasure to drive. However, when the vehicle is stationary and idling, there will be the normal hum of the motor then a "tock" sound. It is rather faint
and can only be heard when sitting in the car with the doors closed, I cannot hear it when I lift the hood. I read in some places that it could be a sticking valve, or something similar and to remedy this add extra oil or synthetic. Well the problem is that I just bought it and the service information is unavailable. At this point I do not know whether its running on mineral or synthetic oil. I don't want to add one or the other and cause any damage, as the car does have 80k on it and may be a little more sensitive than a newer model. Any suggestions..
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Does it go if you pump the brake pedal and hold the pedal down ?
Nick
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jclaw05 wrote:

Are you describing a noise that is tied to engine speed? If you rev the engine a bit does it go away?
You may be thinking of the VANOS noise. It seems to happen if you use too thin an oil. The M50 engines seem to need at least a 40 weight oil (second numvber in multi-vis like 15W40) to build adequate oil pressure. 20W50 is fine for your car too as long as the temps are not too low.
--
-Fred W

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Thanks Fred, I appreciate the info.
Fred W wrote:

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to the oil of your choice.
Sylvain.
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jclaw05 wrote:

Pick whichever oil you want to run in the car from now on and just switch to it. Synthetics and conventional oils are always compatable and will not cause any harm at all to have a little of one left over from the draining.
Because of the symptoms you describe, I would suggest you try using a 15W40 oil (conventional) unless the temperature will be below freezing regularly. In that case, I recomend running 5W40 full synthetic oil.
I do not recommend using 10W40 conventional oil (ever) as the viscosity modifiers break down too quickly and you end up running too thin of an oil after a few thousand miles. Convetional 10W30 is only recomended from 0 deg.C up to a temperature of 10C (50F), so is not very useful either.
By the way, this same information can be found in the owners manual for your car, as well as the BMW TIS if you have access to one.
--
-Fred W

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Thanks for the information, I was just really concerned about the possibility of changing to a different form of motor oil and the possibility of adverse effect, i.e. leaks. Based on your recommendation I will simply change the oil and use 15/40.
Also, another question. Based on the aforementioned problem and, if in fact, the oil weight is the determining factor causing the VANOS effect. Would a thinner weight oil also contribute to the car requiring a greater period of time to turn over and start. For example, in the morning the car takes a considerbly longer time to turn over and start than in the afternoon. It seems that when the car sits for 10 hours +, it simply does not fire up as quickly. This raises my brow abit. Would a thinner weight motor oil prevent a quicker start due to the combination of overnight inactivity and dropping overnight tempatures. I am fearful that this may be a major problem, I live in the N.E. US and the temperature drops considerably over the course of winter. Any thoughts.
Fred W wrote:

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jclaw05 wrote:

Actually, it would be quite the opposite. That is, a thicker oil (one with a higher first number) would likely make the engine harder to start when dead cold. Of course the effect will be increased as the temperature gets lower, hence my recommendation for using 5W40 sythetic in the cold dead of winter and 15W40 conventional during warmer months.
If you do not need to change your oil seasonally, then stick with the 5W40 synthetic year round as it gives you a nice low weight oil when cold, but also has a high viscosity when hot.
BTW, pretty much all cars take a little more cranking when stone cold. It takes a while for the fuel pressure to rise, plus the ECU has to increase the dwell on the injectors for the cold condition. In other words... they all do that. ;-)
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Thanks, after posting my comment I realized it rather counterintuitive to think that a lighter weight oil would produce such results in colder weather. I've always owned VW's and have always been acutely aware of any change in my car, i.e. noise, smell, handling, etc. I've never owned a BMW and am trying to get a flavor for their quirks, shoulds and should nots. Thanks for the info, I appreciate it.
J Fred W wrote:

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