Greetings to all, I've been reading this forum for quite a while and finally decided to join. Within the many great posts, occasionaly there are points stated as if they were factual that are totally incorrect. Although the facts I mention below have been said before in other great posts, I thought it may be helpful to lay them out as a topic in itself. 1) Myth #1 --"Hig viscosity oils flow through the oil lines slower than low viscosity ones (at a give pump speed)". Fact: Automotive oil pumps are positive dislacement pumps. They do not operate like centrifugal type pumps. PDPs will pump any substance a given amount of distance for each turn of the impellers!!!! Therefore, a high viscosity substance peanut buttere will be pumped the same distance down the oil lines as a low viscosity motor oil per turn of the impellers. Now please also note that the impeller speed is determined by engine speed. The difference then is merely that a high visocity fluid will require more energy loss at the pump to do it's work. This is not my opinion, this is a fact and is the nature of the pump design. It is physically impossible for it to be different than I say with a PDP. Caveat, once oil is out of the pressurized lines, the flow of lubricant (splashing nature, dropping under gravity for valver guides, etc) is affected by it's viscosity. Thus any lubrication demands that are related to unpressurized flow of the lubricant may/will be affected by lubricant viscosity. 2) Myth #2 "Oil temperature (sump temp) is not affected by ambient conditions (air temperature)since the engine is water cooled." I love this one. OK, to those that believe this one, did you ever consider what cools the water? Gee... maybe it's the ambient air and that's why there is a radiator? Did anybody watch the F1 Grand Prix this weekend? All the teams had to open up more cooling air to the radiators to compensate for higher air temperatures!!!....but the engines are water cooled so why should they have bothered???? Answer: As the air temperature goes up, the ability of the radiator to cool the water is diminished. However, we don't have the luxury of changing our radiators cooling capability like the Grand Prix teams do and most of thus, run higher sump temps when the ambient temp goes up. In engineering terms, if you had an infinite source of coolant of water (like a lake), this myth would be true cause you could continually supply cool water ad infinitum. However, the water cooling system has a finite reservoir and the coolant entering the engine gets hot (unlike the lake example). The water is cooled in the radiator but what factors control the energy flux (also known as power in units of joules/second or BTU/sec in the English system --- energy/unit time = power) that can be removed from the water? The answer is that the finite cooling capability of the radiator is controlled by radiator size, ambient temperature [wow!!- shouldn't matter right?], and vehicle velocity. The latter is why you can run hotter water and oil temperatures in stop and go traffic. Some cars get taxed enough that they overheat with high ambient temperatures and low air flow (idling) and yes, the oil gets hotter too!!! In fact debunking this ridiculous myth is more important in modern cars than older cars. I read a good study one time on engine cooling where it said that older cars, like the 73 Dodge Dart received about 1/3 of the engine cooling by air circulating under the hood!!! This is when car were not low to the ground, no spoilers, etc!!!! Modern cars do not get as much cooing to the engine further taxing the radiator cooling system and helping to raise overall operating temperatures. ALso, the sump itself used to get much better air cooling with the flow under the vehicle. Some cars, like the 1981 BMW 528i had large cast magnesium oil sumps with cooiling fins on them. Now to specifics, some cars have higher radiator cooling capacities than others relative to engine heat generated. In reality, these cars may not show any real big change in water or oil temperatures until conditions get more extreme (eg. ambient over 100F). Others will show higher oil temps at 70F versus 60F ambient (given otehr common factors (speed, etc). But the average car will run much higher oil temperatures idling on a 110F day in Phoenix than the same car would going 55 MPH down a highway when the ambient temp is 30F. Some folks here have oil temp gauges and have seen this. As the air temperature goes up, the ability of the radiator to cool the water is diminished. Race teams deal with this every weekend by opening up more air to the radiators when ambient temperatures go up. We do not do this to our street cars. They do this to cool down metal, water, and oil temperatures which otherwise would have gone up due to the ambient temp change. Those who believe myth #2 must think the temas are stupid for adding more drag to the cars since oil/metal/water temps are independent of ambient conditions. 3) This point has been made time and time again by good posters here but many posts contunue to show that it is still not understood. Viscosity is extremely sensitive to oil temperature such that a guy making long trips in a hot climate with 15W-50 oil has a much lower viscosity lubricant during most of his trip than a guy making very short trips in the Saskatchewan winter with 0W-20. As simple as this may seem, it is clearly not acknoweledged by many here. Thus, factor your trip length, trip type (stop and go?),ambient temperatures, etc in your lube selection.