Re: [MBZ] Pressure vs flow
David Brodbeck wrote: Even my '89 VW Cabriolet has a note in the owner's manual to avoid high RPM until the oil temperature is over 50 C, which corresponds to the bottom peg on the oil temperature gauge. I seem to recall hearing that some cars had a three-state temperature light that would light up blue at cold temperatures to remind you to take it easy, but I can't recall which ones. Sometimes I wonder just how high the oil pressure in a Mercedes gets after a cold start. The gauges only go up to 3, of course, so we can't really know. I believe the pressure relief on a 617 is around 6.5 bar. Mitch.
Re: [MBZ] Pressure vs flow
And Mobile 1 won't help a bit if the issue is gasoline wash down. The issue is not lack of oil pressure at start up. You are right. It's not pressure but flow that is the issue. According to ExxonMobil, the whole idea of 0W40 or 5W40 is immediate lubrication everywhere in the engine when the engine fires and 10W30 something or 15W50 does not provide this. What you have not considered is that modern gasoline engines start almost immediately at low temps and they need lubrication right now. And it's Mobil, not Mobile which is a town in Alabam. RLE
Re: [MBZ] Pressure vs flow
Speaking of pressure vs flow, I remember hearing that in the 70's, Alfa Romeo had big warnings in their owner's manuals about not exceeding 2000 rpm until the oil pressure came down off the peg at idle -- seems that oil in those days was viscous enough at low temperature that there was essentially no flow to the cams until the engine warmed up, and if you ran the revs up to 6000 cold the cam lobes wore off pretty fast. Gasoline dilution of the oil isn't a problem any more unless you have a pressure regulator fail and dump fuel into the oil. A leaking float valve on a carb, however, can do nasty things to an engine -- a friend on mine bought a work van, a mid 70's Dodge, with a two barrel carb. It flooded all the time, so he asked us to fix the carb -- sure enough, when you started it, fuel was running out the emulsion tube intakes and down the throat. Easy rebuild, but when we got it running it only had 5 psi oil pressure, went up to mabe 15 at speed -- 8 qts of oil in a 6 qt pan, at least half a gallon of gasoline in there. Luckily it didn't explode before we got the oil out. Peter
Re: [MBZ] Pressure vs flow
Peter Frederick wrote: Speaking of pressure vs flow, I remember hearing that in the 70's, Alfa Romeo had big warnings in their owner's manuals about not exceeding 2000 rpm until the oil pressure came down off the peg at idle -- seems that oil in those days was viscous enough at low temperature that there was essentially no flow to the cams until the engine warmed up, and if you ran the revs up to 6000 cold the cam lobes wore off pretty fast. Even my '89 VW Cabriolet has a note in the owner's manual to avoid high RPM until the oil temperature is over 50 C, which corresponds to the bottom peg on the oil temperature gauge. I seem to recall hearing that some cars had a three-state temperature light that would light up blue at cold temperatures to remind you to take it easy, but I can't recall which ones. Sometimes I wonder just how high the oil pressure in a Mercedes gets after a cold start. The gauges only go up to 3, of course, so we can't really know. My Cabriolet has a 5 bar pressure gauge and it usually pegs out on cold starts. I'm sure a Mercedes does even better.
Re: [MBZ] Pressure vs flow
David Brodbeck wrote: Peter Frederick wrote: Speaking of pressure vs flow, I remember hearing that in the 70's, Alfa Romeo had big warnings in their owner's manuals about not exceeding 2000 rpm until the oil pressure came down off the peg at idle -- seems that oil in those days was viscous enough at low temperature that there was essentially no flow to the cams until the engine warmed up, and if you ran the revs up to 6000 cold the cam lobes wore off pretty fast. Even my '89 VW Cabriolet has a note in the owner's manual to avoid high RPM until the oil temperature is over 50 C, which corresponds to the bottom peg on the oil temperature gauge. I seem to recall hearing that some cars had a three-state temperature light that would light up blue at cold temperatures to remind you to take it easy, but I can't recall which ones. Sometimes I wonder just how high the oil pressure in a Mercedes gets after a cold start. The gauges only go up to 3, of course, so we can't really know. My Cabriolet has a 5 bar pressure gauge and it usually pegs out on cold starts. I'm sure a Mercedes does even better. As long as the pressure is 3 bar or greater, the engine is protected using approved oil in the viscosity that is appropriate for the temps. Using almost any group IV synthetic oil (even Mobil 1 15W-50) and your better off in cold weather than using even an 0W-20 or 5W-20 weight conventional oil. At high temps, the group IV oils also offer greatly improved safety. The over pressure valve on the oil filter and the oil pump open (thus limiting pressure) at around 6-7 bar! Marshall -- Marshall Booth Ph.D. Ass't Prof. (ret.) Univ of Pittsburgh School of Medicine [EMAIL PROTECTED]
