Quote:
Originally Posted by Christ
Viscosity increases, so it's less likely to run out away from where it should be.
I've never had an engine that used significantly more oil or made more noise by going to a lower viscosity oil.
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No no no no.... Frank had it right. Viscosity decreases in logarithmic decay as temperature rises.. Hot oil "feeling" thinner means it has lower viscosity and is more prone to flow.
In a vehicle, the oil is only going to get so hot (as regulated through oil-coolant heat exchanger). OEMs choose the weight of oil necessary to maintain appropriate protection at this expected temperature. Diesel engines in particular have very high specific loading on certain components, most notably camshafts. Changing viscosity on a diesel is a much more risky game vs. a low power gasser. Lots of people are pointing at premature camshaft failures as evidence of VW's mistake of supplying 5w-30 to dealerships for the PD (pump-duese) TDIs - they originally only used 5w-40.
Nice vehicle acquisition though, good luck modding. If you are ever less than 99% sure about something TDI related, do ask over on tdiclub.