I just received a flame email from a fellow member that will remain nameless. He took exception to something that I stated ...and to his credit..brought it up to me privately instead of flaming on the board. OTOH ..he's still a flamer and since I'll keep him nameless. I'd like you to critique his assertions versus my knowledge and experience. Here's the meat of my assertion. Oil pumps are typically positive displacement pumps. XX rpm ..XX volume. I've never heard of a centrifical engine oil pump. Vaned, "crescent" ..and perhaps some other vane/rotor type, sure. All have a pressure relief typically built in to limit pressure under all conditions. Here's what I said:
What is the oil pressure relief?
quote:Granted this is a simplified and not necessarily complete explanation ..but I don't see any error in my assertions. This is the email I got (edited to protect the flamer): I suggest you stop giving advice and go back to school. So, if the oil pump is mechanically connected to the crankshaft, if the oil pump is a positive displacement pump as you so mistakenly pontificate, why does the hot oil pressure drop at idle? True, because there is a drop in viscosity, oil more easily leaks out all the bearing surfaces, but, if you'll pull your head out of your butt for a second, you'll also realize that the same seal condition that occurs at the bearing journals occurs at the oil pump where the pressure is generated! Positive displacement? Please guy, you are dating yourself. (as far as years of experience goes) Next you'll probably tell me that pistons are positive displacement and don't leak down too! Yeah sure, blowby doesn't exist! You should apply for a BITOG administration job! You'll for sure, . . . raise the bar! Please either allow this guy to quietly simmer in shame ..or publically humiliate me. [ July 10, 2004, 06:56 PM: Message edited by: Gary Allan ]
Basically, within certain limitations, it sets your MAX oil pressure. Oil pumps are typically "positive displacement" type pumps. If it turns one rpm ..X amount of volume MUST be pumped. So, if you've got straight 50 weight and it's -40 out ..you're going to probably break something if the oil pump trys and move the full volume of oil. They have a built in relief valve that bleeds all excess volume via (typically) spring pressure ..back to the suction side of the pump. So the pump turns ..the max flow goes to the engine that "can" go there at that max pressure/at that temp-viscosity (let's take mine, 58 psi, for example) and the rest of the volume (that is causing the high pressure) is shunted to the pickup side of the pump.