Rock

My car runs warm to begin with. I use royal purple 20w-50. Ive noticed it consumes less oil even while beating on it this way.

I like the heavier stuff. Its almost a no risk insurance against 5w-30. Ive heard people claim bearing failures to lighter grade oils.

Cory9584

I tried 5-30 when i first got a 951 and found it broke down very quick so now i use 10-40 and it seems to work well on the street summer and winter.

Chris White

There is a little more to this than most folks know.
The 'recommended' viscosity should be based on the bearing clearances and temperature range.
Most folks are stuck on the oil pressure issue. In reality 10 psi at the crank is all that is needed. In fact 6psi is a commonly accepted minimum – but remember, that is at the crank. Because of the oiling system you need a bunch more oil pressure before the crank to assure that you meet that minimum.
You want to run as light an oil as possible to assure that pressure…why? Because the thicker an oil is the less volume you will see at the same pressure. This is important because oil is a coolant too – the more oil volume you get through the system the better the cooling at critical areas. The oil is actually cooling the bearings directly, if you take this to the extreme and put it 90w oil you will see great oil pressure but very bad flow rates. The pressure will read nice and high – making you think that all is well, when in actuality the bearings are getting much hotter and the oil at the key bearing surface is over heating.
The other interesting oil issue is that the main thing you need to worry about is the oil pressure at the hydrostatic wedge area between the crank and the rod bearing– and that is not really determined by the oil pressure but by the flow. Low flow and high pressure may actually cause an oil starvation issue at the bearing.
Final point…if you really care about your modded 944t engine you will add more oil cooling and not run a very thick oil.

seattle951

This is the point of veiw of the mechanic who built my motor. He installed an extra oil cooler and had other modifications done to the primary cooling system. His view was that we needed to focus on getting heat out of the system. He has scoffed at 20W 50 since the beginning since it would not flow properly at operating temperature. He has been recommending 10W 30 synthetic since day 1.

333pg333

Yes I would agree that the film strength is vital and if it were proved that a 10w/30 could offer sufficient coverage I would consider shifting my opinion.
Why, if there is a potential issue with oil flow to the bearings, did the factory recommend 20w/50 in most conditions? Also, assuming that as your temps rise even the thicker oils become hot and flow better just like the lower visc oils become too thin and stop offering much protection at all? Why did the factory run their racecars on Shell straight 50w or 60w even when they had M1 emblazoned on their flanks?
I get what you're saying Chris, but am confused as to what you'd recommend based on your last 2 posts?

Chris White

two different situations – real race cars only run at full output and many even heat the oil before running out on the track – that’s a lot different than a street engine.
He factory was ‘covering the butts’ for a worst case scenario – if you ran a stock 99T full throttle for the length of the autobahn you would really need the heavier oil since the oil temps would be north of 250. A non synthetic oil does not like temps over 250 and will start to break down. The dino oils of the 80’s would have thinned out and a dino 10/30 would have had real problems.
The ‘real’ answer is that there is a correct oil viscosity for different bearing / rod clearances. And oil temp operating ranges.
What I recommend is getting the right oil for the right job and the right amount of oil cooling for the application. If you are losing oil pressure because the oil is too hot then going to a higher viscosity is not the correct way out. In fact by deceasing the oil flow you can actually increase the oil temp. Your oil viscosity should be selected based on bearing clearances, oil cooling capacity and oil type.

Euro951

0-30 mobil 1 is way too light.... and I am sure your oil pressure decreases once your car is up to operating temperature. In my experiences with my autocross Miata a Royal Purple 10w30 provides and sustains more oil pressure then a Mobile 1 10w30. I am sure it is because of the different additive package which Royal Purple uses.

I run many of my vehicles up to redline every time they are removed from the garage and I don't like seeing my oil gauge show low oil pressure. I will always error in the side of caution ( heavier weight oil)

If you go to any race track and talk to mechanics many will also swear by using dino oil with ZDDP content. They just replace it after every race.

Just my two cents

DanR

oil is probably the subject that will never get agreement on. I had started to listen to the forum talk and was thinking about usint 20-40 at my next oil change but have decided that I do not know best from what I read on a forum and will stick with the advice from my engine builder. Staying with 15-40 Mobil 1

Cant wait fro the flame heading my way now

reno808

Dan did you remove the bolt?

seattle951

I ended up ording XPR 5W-30 online and got around to changing the oil this afternoon. The RP oil is certainly different. It comes black out of the bottle and feels different to the touch.

It was about 65 degrees today and I took the car for a drive. I have a favorite stretch of deserted road that I use to push the car. I managed to get it to the second bar on the temperature gauge breifly before it cooled down. At idle, the oil pressure never dropped below about 3 and quarter.

The car also showed an improvement at cold start up. With 20W-50 I get lifter noise for 20 seconds. With 0W-40 and 5W-50 I get noise for 10 seconds. With the RP XPR 5W-30 the noise was less than 5 seconds.

eniac

My statment is who do you wanna believe? Myself I go with what Porsche says...afterall they built the car and had to do handle all the warranty work the cars sold when new. Where did the guy at Royal Purple get the info that 20w50 was ok for air cooled 911's and but not ok for 951's? How many tests did Royal Purple do on actual 951 engine? How much testing do you think Porsche did on 951 engine when designing them?

Choose who you want to believe, the company that built and designed the engine(and we're not talking Ford, this is Porsche) or the guy tryin ta sell ya'all sum oil fer yer car.

Ima go with what Porsche recommends.

seattle951

When Porsche came out with the 951 in 1985 (model year 86), they recommended 20W 50 and other weight oils. That was nearly 25 years ago and oil technology has changed dramatically. According to Panaroma magazine, Porsche now recommends 0W 40 synthetic for the 951 primarily because of rocker noise on start-up.

Royal Purple had nothing to gain by recommending 5W 30. They also make 20W 50 and charge the same price for either oil.

Royal Purple may not make the recommended oil list for many cars because of the 2x to 3x price and difficulty in getting it. While the standard oil is available a few places in town, the race oil (XLR) requires a special order. Many car makers may feel that it just not practical.

As mentioned, opinions vary depending on which source of information you trust.

billthe3

Ok, on the topic of oil related stuff...

I've been running RP 20w-50 for the last oil change, and noticed that the pressures would never really lower down (only got to maybe 3.5 bar on the stock gauge after a good hour plus of driving without good cooling - hot days or non-highway driving) and never had any real issues with burning oil or whatnot. However, I did have an issue with my oil filter coming unscrewed on at least two occasions, and my oil cooler housing has started to leak much more than it was a year or so ago. Could the increased pressure be enough to blow out the oil seal and possibly unscrew the filter? I'm going to switch down to at least 10w-40 for this next batch of oil since its colder now.

333pg333

" According to Panaroma magazine, Porsche now recommends 0W 40 synthetic for the 951 primarily because of rocker noise on start-up. "

Ha, I'd love to see that article??

Chris White

Damn, I keep forgetting to put the rockers back in when I rebuild an engine....