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<x-charset iso-8859-1>Hello- > Has anybody got any research on operating oil temps? Indeed! I've done tons... and lots of testing, too. > How to control them? Oil coolers that work. :-) No, seriously, IMHO the first problem with the stock VW oil cooling system is the silly pressure-controlled thermostat. When you start changing oil weights, pump sizes, sustained engine rpm, etc. it'll start allowing oil to bypass the cooler even with the engine fully warmed up. From day one, the 911 used a REAL thermostat to control flow to the cooler. > What does oil temp actually prove? Oil temperature proves oil temperature. I know, it sounds like a stupid answer, but it's true. It does NOT prove "engine temperature." Remember - your engine is aircooled, NOT oilcooled. Since measuring the air outlet temperature is pretty useless, the best thing to see "engine temperature" is cylinder head temperature. Putting one of these gauges on a VW is somewhat common, and is VERY useful. Oil temp has NO reflection on head temp. I've done testing, including some using NO oil cooler, and proven this several times over. High oil temps are primarily due to high sustained rpm, and secondarily due to high sustained load. In practice, you'll always find the former to be more prominent than the latter. High head temps are primarily due to high load. In other words, a climb up a mountain at WOT at 2500rpm will leave your oil feeling pretty fine, but your heads will be VERY warm! > What they should be per application, what effect for too high or too > low? There are two things you want from your oil temperature: a temp that gives a good thermal stability and a temp that gives a good viscosity. The first of these is easier to explain - basically, you don't want the oil to bake to a crisp. As a rough rule-of-thumb, conventional oils shouldn't be used over 250F for a sustained amount of time for this reason. Synthetic oils are good for much more - I've sustained 300F with synthetic oil without much recourse. The second thing, the viscosity bit, is more difficult to explain. What you need to understand is that there is a STRONG temperature dependence on the viscosity of any oil. You can make a little x-y plot of temp (x) vs. viscosity (y), and see exactly what's going on. For you math affectionatos, as a very good approximation, we can assume that there is an exponential dependence in the normal operating range, i.e. a semi-log graph yields linear plots. For those less affectionate with math, it just reaffirms that there is a STRONG temperature dependence on the viscosity of any oil :-). This kinda sucks, as it'd be best to have the oil be the same viscosity always. That way, you could design your bearings perfectly and have them last forever, but that's not reality. The problem is that when cold, oils are typically too thick (yielding high drag losses and if cold enough bad flow characteristics). And, when hot, oils are typically too thin (which lowers the allowed load on the bearing before the oil film breaks down and the bearing more-or-less touches the journal, leaving it to rely on the "boundary lubrication additives" alone to guard against major wear). What's the next best thing? An oil with a lower temperature dependence! Hey, that's what a multi-weight oil is! :-) > I haven't been able to find much on the internet, but then again, I > may not be looking in the right places. Here's some rough rules-of-thumb: Conventional straightweight oils: use them for breakin only and get them outta there - they are the worst oil around in our technologically- evolved era. Conventional multiweight oils: 20w-50 is a pretty good choice for most people, and keeping it around 190F-225F (after the cooler, i.e. the dipstick thing isn't *that* useful) is great. If the peak temperature hangs up around 250F for long, that's not too groovy. Synthetic oils: 190F-250F is usually fine for a decent weight (5w-30 you may want to keep cooler to keep the oil pressure up). With regard to thermal breakdown, don't worry: you'll likely get low oil pressure before it begins to thermally decay :-). The above few statements are semi-blanket statements. To be more specific, you need to outfit your car with a bunch of gauges (kinda like I have :-). Take care, Shad Laws LN Engineering http://www.LNengineering.com ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/ </x-charset>