Quote:
Originally Posted by anom3
there is no doubt in my case this is somehow related to the oil system.
after switching over to 0w40 the noise is much different.
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The thing is, my car at >50k miles doesn't make this noise with 10W60.
So it would seem likely that some component of the VANOS in your car has worn to an extent that it produces the noise. Its not out of the question that using an oil with a lower viscosity will affect the way the VANOS functions to some degree. The VANOS is driven by the oil pressure from the main oil pump which is a constant flow type with a pressure relief valve. At normal operating temps the oil flow rate will be the same whether you use 0W40 or 10W60 (the oil pressure created by both oils being lower than the pressure relief setting) however in a cold start the flow rate will be higher for a 0W40 than the 10W60 as the thicker oil will hit the pressure relief setting before the thinner oil....although I don't know what the effect of that would be on the VANOS.
Quote:
Originally Posted by anom3
i know the E46 and E92 vanos differ very much (high pressure vs low pressure etc etc), but i would not be surprised in the slightest if the E92 vanos retained some of the properties of the high pressure vanos... like the cold start procedure...
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IIRC the ECU for the E9x M3 is produced by the same company as the one for the E46 M3. I think it is normal that some software would be carried over and the cold start procedure is likely to be one of them. As I noted the E46 M3s ECU does not look at the VANOS until two seconds after the engine has fired so it would be a massive coincidence that the noise heard in the E9x M3 just happens to occur at a couple of seconds after the engine fired if it wasn't a function of the same start procedure.