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I know this is a third topic on essentially the same subject but I find that once the initial question is answered in one thread folks often tend to ignore additional questions in the thread.
I am using 10w40 in an old somewhat tired slant six (no telling how many miles are on it). The oil pressere at hot idle is somewhere between 5-10 PSI, and at highway speed I get a good 35-40 PSI so the pump is functioning. This would all be fine according to the 10 psi for every 1000RPM. My question is, is more oil pressure better? The guy at the auto parts store said that I should switch to SAE30, and that my pressure will come up a lot. I live in the PNW where average temperature arnges between about 20F for extreme low and 90f for extremem high. Is this SAE30 good for such a climate?
In 30 years I've never run single-grade oil in anything but a lawnmower (and not even that nowdays), so stick with multi-grade oils.I am using 10w40 in an old somewhat tired slant six (no telling how many miles are on it). The oil pressere at hot idle is somewhere between 5-10 PSI, and at highway speed I get a good 35-40 PSI so the pump is functioning. This would all be fine according to the 10 psi for every 1000RPM. My question is, is more oil pressure better? The guy at the auto parts store said that I should switch to SAE30, and that my pressure will come up a lot. I live in the PNW where average temperature arnges between about 20F for extreme low and 90f for extremem high. Is this SAE30 good for such a climate?
As for the pressure numbers- those look fine. Remember that engine oil systems regulate pressure at the DELIVERY end of the oil plumbing system, so the pressure seen downstream is the delivery setpoint-pressure minus the flow loss through the system. Thicker oils have more loss due to flow resisteance, so if you look at the downstream end of the system (the bearings- where it really counts!) there comes a point where thicker oil actually REDUCES both the volume (cooling) and pressure of oil seen at the bearings. Some engines place the oil sending unit far downstream of the oil pump (example: Mopar big-block V8s where the pump feeds the passengers side front of the system, and the oil pressure sender tap point is at the rear of the engine) and you can SEE this effect on the guage to an extent. Conversely, too thin an oil will bleed out the bearing clearances too rapidly and won't fully pressurize the system.
I tend to avoid 10W40 oils because they used to require so much more viscosity modification than 10w30 or 20w50, but with today's oils that are orders of magnitude better than 80s oils (let alone 60's oils!) I wouldn't be concerned. Just don't use bargain-basement oil- go with a name-brand like Mobil, Castrol, Valvoline, etc. And I wouldn't use one of the "botique" oils that are aimed at maximizing EPA mileage numbers, either- for example that 5w20 monkey pee that Ford pushes to boost its CAFE computations just a little bit. For most of the world, 10w30, 20w50, and maybe 5w30 are fine for vintage Mopar engines. In synthetics, heck you can use anything. 0W30 Mobil-1 is a very good oil.
If you want to become a real "oil nerd" and always use the oils that are giving the very best used oil analysis results, go hang out on the www.bobistheoilguy.com discussion boards
I never ever refill, when level starts to go down I change it. That happens about 3 or 4 months after I changed oil. Let's say that I put about 3k miles over each oil change.
