is 20/50 oil really needed on a fresh engine

[cmcfaul]

Having just rebuilt my engine I am concerned with too much oil pressure...good problem to have as apposed to the opposite:-)

Oil pressure is perfect when the engine is at temps. Basically getting close to 2X RPMS (3,000 RPM's = 60 oil pressure).

When the engine is cold I really have to short shift to keep pressure from pegging. As it gets cold outside I see this being a bigger issue.

So my question is, on a fresh engine is thick 20/50 oil really correct? Might a thinner 10/40 or less be more in line with new, tight bearings etc?

Thanks,

Chris
73 911 E

[cmonref]

When the engine is cold I really have to short shift to keep pressure from pegging. As it gets cold outside I see this being a bigger issue.

Your actions when the engine is cold are right on. At "pegging," the overpressure piston is bypassing oil, thus maintaining the "pegged" pressure. Keeping the RPM down when the engine is cold, as you do, helps prevent higher flows and potential higher pressures.

For an air cooled engine, live with the cold engine, high pressure limitations to insure you have the required lubrication when the engine is hot.

[E Sully]

In the original drivers manual, Porsche specified straight 30wt summer, 20wt winter, and 10wt below 5 degrees farenheit. I have used 10w-40 in the cooler weather.

[cmcfaul]

Typically I change the oil in the spring so it is nice and thick for the summer and a bit thinner for the winter. Having just rebuilt the engine and done a couple oil changes since it is thick and pressure is high when cold and to spec when hot.

Last winter on a VERY cold day I popped the oil cooler likely because of too much pressure. That was pre rebuild and oil bypass mod but not something I want to repeat.

I will keep doing what I am doing and shift by pressure gage. I do think 20/50 oil is too thick as a winter oil but I am not changing it again.

Thanks,

Chris
73 911 E

[fanaudical]

Dumb question, but are you sure your oil gauge is reporting the right readings? I was seeing similar behavior but have determined my oil sender is not working right (still need to replace it, though).

[cmcfaul]

fairly confident it's accurate. The sensor is brand new and I ran a dedicated wire directly from it to the gage. The sensor might be a little optimistic as it indicates a bit more pressure then the one it replaced.

The old one was not working so I replaced it and found the new one did not work either so replaced the wire between it and the gage and all is good.

Chris

73 911 E

[KTL]

Many of the recommended good oils for our engines are 15W40 grade. So if that makes you feel better, go with it. But ultimately the overpressure valve is going to dictate your oil pressure at higher rpms.

I would feel MUCH more comfortable running a 20W50 or 15W40 multigrade, especially in hot weather, vs. a single grade. My recent engine failure I believe was partly attributed to the 30WT break in oil not providing the necessary film strength. Shoulda switched to the tried and true 20W50 before going very hard on it.....

[911pcars]

Originally Posted by cmcfaul

Having just rebuilt my engine I am concerned with too much oil pressure...good problem to have as apposed to the opposite:-)

Oil pressure is perfect when the engine is at temps. Basically getting close to 2X RPMS (3,000 RPM's = 60 oil pressure).

When the engine is cold I really have to short shift to keep pressure from pegging. As it gets cold outside I see this being a bigger issue.

So my question is, on a fresh engine is thick 20/50 oil really correct? Might a thinner 10/40 or less be more in line with new, tight bearings etc?

Thanks,

Chris
73 911 E[

When cold, a multi-vis oil should act like a 20 wt. oil. How cold are your ambient temps?

If the oil pressure is pegging with 20-50, keep the rpms down until the engine has fully warmed up.

Sherwood

[Reiver]

I live in Az so the weather now is mid 80's and that's too cool for 20w/50 on my fresh 930-10 SC.
I use 10w/40 when it cools and use the 20w/50 when we are in the 90's-100 +.....I see very little dif in oil pressure with the change once warmed up...the diff is on start up.

[911pcars]

Originally Posted by Reiver

I live in Az so the weather now is mid 80's and that's too cool for 20w/50 on my fresh 930-10 SC.
I use 10w/40 when it cools and use the 20w/50 when we are in the 90's-100 +.....I see very little dif in oil pressure with the change once warmed up...the diff is on start up.

My daughter is going to school in AZ, so I understand people's relative perception of temperature. At the same time, people on the east coast and northern locations are probably chuckling at your description of cool weather (mid-80's), especially in their winters.

Being from a more temperate climate of SoCal, I suggest mid-80s as warm enough for 20-50 oil, but then our temp. swings are closer but not as wide as yours. Once warmed up, the engine really doesn't care what the ambient temperature is unless it's +90ºF.

However, in the desert, it can be "cold" in the winter months (what, 45?). If the daytime temps swing 60 degrees, I suppose 15-40 would be fine, but 20-50 would offer more protection depending on your driving conditions and max. ambient temps. The charts say typical low-high temps in AZ, 45-105ºF.

Sherwood

[KTL]

Agree w/Sherwood on the usage of 20W50. We run 20W50 all season (April thru November) in our engines. Early spring it's pretty cold in the morning & same goes for late fall. Sometimes we are "defrosting" the cars first thing in the AM at the track. Never have problems with 20W50 being too heavy.

Re-read the thread again and noticed Chris mentioned he developed an oil cooler leak at cold startup. This should only happen when a t-stat is malfunctioning. The t-stat(s) (some 911 cars have one, some have two) are there to protect the engine-mounted oil cooler and also the external front oil cooler. There's no flow going thru these coolers until their respective t-stats open at 83C (180F)