OIL PRESSURE
07-13-2011, 04:49 PM
#17
Race Director
All car engines depend upon the same fluid dynamic principles. It is not like the Turbo can exist in its own world in which these do not apply.
If your car's engine oil pressure if fluctuating, if the low oil pressure light is coming on and you are sure the oil level is correct, the engine has the proper type of oil in it and the oil is reasonably fresh (oil can lose its viscosity over time due to water/unburned fuel contamination) then you need to verify the oil pressure monitoring/reporting system is working properly. Most of the time the low oil pressure cause is a sensor or wiring problem.
But if it is not then the oil pressure needs to be checked with an oil pressure gage at the engine or at some oil pressure test point (usually at or near the block) and the real oil pressure readings noted.
If they are not in spec (too low or less common too high) the cause needs to be found and fixed.
Running a heavier oil is a bad idea, it is an attempt to mask or make believe a problem doesn't exist.
Another risk is the heavier oil while it might bump up the oil pressure the flow may not be that much and other portions of the engine may suffer from lack of oil and those areas that were ok to begin with will soon not be.
For instance, the camshaft lobes and their mating lifter faces are splashed lubed from the oil that comes from the lifter bodies that is around the lifter body and its bore. (That is at least the way my Boxster engine's cam lobes are lubed and I think Porsche used this same way in its other car engines.) A heavier oil may have this oil flow curtailed or the splash pattern affected so the cam lobes and lifter faces run with an unsufficient supply of oil.
Sincerely,
Macster.
07-14-2011, 03:01 PM
#25
Burning Brakes
Thread Starter
If the " relief valve spring " is the cause then the higher temp will cause the spring to be softer. High temp will cause the piston to be tighter also. Old pistion showed slight wear marks. The upgrade piston is tappered...less friction?
07-14-2011, 03:56 PM
#26
Race Director
The piston gets larger as it heats up, but so does the hole it fits in. Both the piston and the surrounding metal run at the same temp.
However, what can happen -- I've observed this in other assemblies -- is a small diameter hole in a large piece of metal, as the metal is heated up say with a rosebud torch tip (used to preheat items prior to welding them) the hole's diameter will shrink slightly as the metal heats up unevenly and the metal that surrounds the hole expands.
But once the entire block of metal is at an even temp the hole's diameter returns to its size.
But in the case of this oil relief piston and its bore, it is fed oil, high pressure oil, and the heating up of both the piston and the surrounding metal is fairly even. The piston's fit in the bore is a sliding fit and this takes into account possible uneven growth from heat: The piston getting a bit larger while the hole remains the same size or even gets a bit smaller for a while, until the temperature gradients diminish.
The scoring can come from metal to metal contact but more likely is from particulate matter in the oil that gets between the piston and the hole it fits into.
The tapered end may be a nod towards addressing possible uneven heating or it may just be a way to make it easier for oil to make its way between the piston and the hole in which it fits.
Sincerely,
Macster.
