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Car Forum / BMW Cars / April 2005Cold engine max REV
Hi, Everyone know that when a engine (oil temp) is cold we should not take it to high revs as the oil is still thick and doesn't do it job right. My question to anyone o knows more about the subject is, what is considered high revs? As a rule of thumb I try to avoid reaching 50% of the redline marked value. My E36 316i redlines @6000 rpm, so I don't exceed 3000 rpm when cold, especialy in the lower gears. The E46 M3 has a led system in the rev counter that indicates the current redline limit for the current engine temp, and the red line is behond the 50% range when cold. Any comments on this? HangaS Synthetic oil that's 5W30 shouldn't be a redline issue as long as you're not living at the North Pole. The issue with synthetic is it tends to run off parts so when you initially start the car, the oil coating on the cylinder walls etc may be thin. But in a few seconds the oil pressure is up and you're redy to go. > Hi, > [quoted text clipped - 17 lines] > > HangaS > Synthetic oil that's 5W30 shouldn't be a redline issue as long as you're not > living at the North Pole. The issue with synthetic is it tends to run off > parts so when you initially start the car, the oil coating on the cylinder > walls etc may be thin. But in a few seconds the oil pressure is up and > you're redy to go. That's a new one... where did you get that information from? I have always heard that synthetic oil coats engine parts better and causes less wear at initial start-up. This only makes sense since the oil viscosity is maintained at high temps better than conventional oil, and the engine is at high temp when it was turned off. The fact that the oil is thinner when cold only makes the oil pressure come up faster when the engine is first started. -Fred W Take a kitchen knife and dip it in synthetic oil and hang it up for a few hours then do the same with another knife and dino oil. See which one has more of a coating. Dino oil and synthetic of the same class, like 5W30, will be of the same viscosity as any temperature. And you're right, lower viscosity oil should be lubricating the engine more quickly than higher viscosity oil. But there's still that time between the movement of the piston rings and the arrival of the oil flow. Synthetic just doesn't break down from heat as quickly as dino oil and so provides effective lubrication for longer periods. > > Synthetic oil that's 5W30 shouldn't be a redline issue as long as you're not > > living at the North Pole. The issue with synthetic is it tends to run off [quoted text clipped - 12 lines] > > -Fred W > Take a kitchen knife and dip it in synthetic oil and hang it up for a few > hours then do the same with another knife and dino oil. See which one has [quoted text clipped - 5 lines] > down from heat as quickly as dino oil and so provides effective lubrication > for longer periods. John, The above experiment *might* be valid if the oil was at room temperature when you shutdown your engine. Obviously it is not. In order to do perform that experiment correctly you should heat both oils in a saucepan to 190 degrees F or so and then see which runs off faster. It will be the conventional oil. You see, all oils get thinner with increased temperatures. That's simple physics. The big *advantage* of synthetic oils over conventional ones is that it can maintain viscosity better at increased temps while also being considerably thinner at lower temps. If someone could somehow invent an oil that the had reverse temperature characteristics they would surely become rich. -Fred W > > Synthetic oil that's 5W30 shouldn't be a redline issue as long as > > you're not living at the North Pole. The issue with synthetic is it > > tends to run off parts so when you initially start the car, the oil > > coating on the cylinder walls etc may be thin. But in a few seconds > > the oil pressure is up and you're redy to go. > That's a new one... where did you get that information from? I have > always heard that synthetic oil coats engine parts better and causes > less wear at initial start-up. This only makes sense since the oil > viscosity is maintained at high temps better than conventional oil, and > the engine is at high temp when it was turned off. I tried fully synthetic in my old Rover V-8 with some 150,000 miles. And if left more than a few days unused, got some what I reckon was big end knock at startup. Not if just left overnight. Changing back to semi-synth has cured this.  Signature*What hair colour do they put on the driver's license of a bald man? * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. |
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