Skip to main content

Replies sorted oldest to newest

What works in your Boxster may kill your aircooled motor. Modern (new SM/SN rated) oils have very little zddp (a zinc/phosphorus compound), which protects the wear surfaces in solid lifter engines. It's been taken out of oils for new cars to keep catalytic converters living longer. As Carl mentioned, Brad Penn has a suitable oil (not just the new motor break-in oil) for these antique motors. You will find others too, when you start looking around. 

I was talking about the weight of the oil not the the type if oil. As I stated earlier...agreed. I am online looking up Brad Penn. looking forward to seeing what VS uses. I cant remember what I put in my last VS when I was changing oil but whatever it was worked well. iI probably have an old thread I should look up!

You'll know you have the right weight oil when the oil pressure is about 1/100 of the rpms when the motor is fully warmed up; 8-10lbs at idle, 20-30lbs at 2500rpms and 35-40lbs at 3500rpm. An oil with a higher final weight number seems like a good idea (more pressure can only be good, right?), but pressure much above 45lbs (when fully warmed up) causes the oil to bypass the cooler. The oil system has no thermostat is pressure regulated only, and this is why the correct weight oil is so important. This is one reason some cars run hot at highway speeds; with most of the oil bypassing the cooler (from too much pressure) it isn't shedding any heat, and the fan can't remove it if it's being held in the oil.

 

The lower the first number, the sooner the bearings are lubricated properly when the motor is cold. Even 10w doesn't have great flow through the bearings immediately at cold start-up. 

 

For a street motor with typical bearing clearances and a 26mm oil pump, in most cases a 5 or 10w30 oil will give proper lubrication and pressure.  

Last edited by ALB

Just to reinforce what ALB said about oil pressure and oil bypass, I did an experiment years ago by running to a local town (ten miles away) and back on a highway (speed about 65mph) and checking my oil temp with a dipstick thermometer just as I got off the highway and again when I got home.  Outside temp was about 90F that day, and elevation was about sea level the whole time.

 

The first run was with my old standby, 10W-40 Pennsoil dino.

 

The second run was with 20W-50 Pennsoil dino.

 

I can't remember the actual numbers (it was back around 2004, IIRC and should be here in the archives if they were ported over to this site) but the temps were consistently 5-10 degrees higher with the 20W-50 than with the lighter grade 10W-40 oil.  I attribute that to oil by-pass right to the sump as the pressure climbs at turnpike speeds and never getting to the oil coolers.

 

Since about that time, I had been running Rotella diesel oil (10W-40 in summer) until last year when I switched to Brad Penn 10W-40 Green (which is a synthetic blend with added sinc and phosphorus, according to my oil guy).  Using either Rotella or Brad Penn, my temps have never exceed 205F and my low oil pressure light never comes on, even at idle after exiting a freeway and pounding it hard to bring the temps up.

 

Oh, and I have a 30mm Melling oil pump with the normal output blocked and pulling output through a Berg 125 pound pressure relief cover. 

 

As an aside, I had an interesting chat with the engine engineer at TRG Motorsports about oils:  They run exclusively synthetic oils in the Rolex Porsches (not just TRG - everybody does) for a lot of reasons needed by their thoroughly modern engines, but one of the biggest reasons is that synthetic oil dissipates heat much faster than dino oil, thereby keeping the engine cooler.  He thought that should work for our older design engines as well (he didn't have a lot of experience with our generation of engines) but also offered that the synthetic oils tend to be "looser", meaning that, for any given temperature, they are slightly thinner than a comparable type of dino oil.  Given that, we might see good results using a synthetic 20W-50 in our looser engines, but I've never tested that out.  I'm happy with my Brad Penn 10W-40 and have a 5-year supply out in the garage - longer, if I start back riding my bicycle a lot more  

Last edited by Gordon Nichols

That's a good point.  I have always run dino break-in oil for the first 500-1,000 miles, then regular dino oil for the next 5k-6k miles, at least.  In fact I've never run synthetic oil in any car until at least 10,000 miles to make sure everything breaks in properly.  

 

See what Roland recommends and do that - he built it and has to stand by it and will want to see it broken in right.

Post Content
×
×
×
×
Link copied to your clipboard.
×
×