oil pressure/oil weight opinions

[GreddySpyder]

I've always used Castrol GTX 10w30 in every car I've owned, and I have yet to have any engine damage. I know that turbo DSMs tend to have low oil pressure, but I noticed something when changing the oil on my sister's 95 GS-T tonight... her oil pressure is much higher than mine at idle. I put 20w50 oil in her engine and her oil pressure at idle is where the yellow line is in the picture below. I use 10w30 oil and my oil pressure is where the lower green line is in the picture below and it rises to about where the upper green line is at full throttle. We both have the original oil pumps in our engine, and my DSM has 87,000 miles on it while hers has 127,000 miles on it, so the oil pressure gain she has obviously has nothing to do with having a lower mileage oil pump.

I've been told by fellow DSMers to not use 20w50 because it is too thick and it won't protect the turbo as well, flow through the engine oil passages as well, etc... But it's hot enough to roast Satan around here so I'm thinking 20w50 might not be such a bad idea. I'm looking for some intelligent thought on the pros/cons of 20w50 vs. 10w30 . By the way I'm starting the switch to Castrol Syntec this oil change, but I'm assuming viscosity is viscosity, so I don't know if synthetic will help oil pressure or not.

 

[91 NT Eclipse]

Maybe you should try 15-40 before going to 20-50. It might work for you.

 

[Defiant]

Don't chase ghosts. Until or unless you put on a pair of real gauges and nice fresh senders, all from the same manufacturer and production batch, don't put a lot into what a dashboard needle says. Factory gauges aren't meant to take over to LeMans- or they wouldn't have thought they needed to add on an idiot light to go along with it.
10W-30 is what the factory calls for, it's the grade they designed for until it gets really cold, and even that doesn't change until below 10°F. Thicker oil won't flow into small spaces so well as thinner, and once into a plain bearing, the hydrodynamics of the bearing will _hold_ the oil in it: your oil pump is to _cool_ the oil, not keep it in the bearing. Left to its own behaviour, the bearing would hold its oil until the heat buildup would bring about the failure of the oil and then the bearing.
A factory oil pressure gauge is meaningless enough on its own, and the more so between specific vehicles. Don't compare needle readings car-to-car, only go by where it runs in _one_ car, and whether that varies over time (current factory gauges are designed to run at a "set point" so when a neighbor rides in your car, he doesn't go running off to the dealership in a panic that his reading is two needle-widths different). Even then, your usual change is in the life cycle of the sender.

Oil pressure isn't an issue on DSMs; 20W50 _is_ far too high-viscosity.

You'll also get a fair amount of static in your choice of Castrol (which hasn't had a whiff of castor in it for forty years, but a name's a name), fully balanced by those who swear it's the "best", and all arguments voided by the API ratings.