ron in sc

Below is a good discussion I had saved about oil. I did not write this so I can not take credit for it. 0W-40 is probably the perfect all around choice for 98% of street driven 993s. I think it does have an Achilles heel that make it not so good for some owners, of whom there is an especially high incidence on the Rennlist forums. To get a 0W-40, even starting with a synthetic base stock, you must begin with a rather thin oil, probably what would be the equivalent of a 0W-20. Then you add viscosity extenders to it, which are long chain organic molecules that unfold as they meet higher temperatures. This keeps the oil from thinning as fast as it would normally as it heats up, and allows it to have the 40 weight rating at 100 degrees Celsius. One problem with viscosity extenders is that they aren't lubricants themselves, so their volume displaces the lubricating base stock, and the lubricity of the resulting oil is actually a little less. The bigger problem is that under high temperature, high shear conditions (high rpm!) these molecules are sheared apart and destroyed - over time. As these molecules are destroyed, the oil becomes thinner at high temperatures, so what was originally a 0W-40 oil starts approaching the viscosity of the original base stock - the 0W-20 stuff. This is not good for continued use at high temperatures and loads. This is probably unlikely to happen to 0W-40 to a significant extent under normal street use within a recommended oil change interval. But if you drive your car hard on the streets of Phoenix in the summer, or regularly take your 993 to the track for DE events, 0W-40 might not hold up very well. This is why track guys like synthetic 15W-50, which has a higher viscosity base stock, and uses little (maybe none) added viscosity extender and will provide proper protection to the engine under "race" type conditions for a longer time than 0W-40. So you see why Mobile 1 0W-40 might be the perfect oil for GJ, but not at all the right one for Greg's race car. There are no simple answers!

My workshop manual give specific instructions, in part it says: “The pressures and temperatures specified in the below diagrams must be reached after approx. 10 mins. operation time at a speed of 2,000 rpm with the compressor switch on.” So I’ll have to get some to hold the accelerator at 2,000 rpm while I read the gauges. Questions: The diagrams gives temps. for ambient. If ambient is temp measured about 2" in front of condenser that’s really not easily obtained due to position of condenser. It’s mounted sideways in an enclosed space. Or is ambient just the temperature outside? Are the pressure readings generally done with the car at idle or does that just very with the auto manufacturer or with the compressor manufacturer? I want to test the A/C system on my Porsche to see if the vent temps are within the range expressed in my workshop manual based on the ambient temps if I can get an accurate way of defining ambient temp.

I’ve just had a set of SO3's put on my 18" Kinesis Supercup Wheels; 40x225 front and 30x285 rear, wheel widths are 8" and 10" respectively. I took off a set of 996 twin turbo wheels that I bought new. They have Pirelli Pzeros fitted; 40x225 front and 30x295 rear, wheel widths are 8" and 11' respectively. My question is whether the tire wear on the Pirelli is within normal limits, not as it relates to mileage but as it relates to evenness of wear across the surface of the tire. That is from the inside to the outside. The car is a 97 C2S which is not driven on the track. Here are the measurements which I took with a tire tread depth gauge: Front: right and left tires had the same readings: inside–7/32 middle–9/32 outside–8/32 Rear: left inside–5/32* middle–6/32 outside–6/32 Rear: right inside–4/32* middle–6/32 outside-6/32 * indicates readings that don’t match from side to side. Car handles fine although it looks like I could reduce front air pressure a little to even wear out but I don’t think for 1/32 of wear it’s worth it. Since I just got new tires I’ve thought about an alignment, but I don’t think my tire wear is that bad. Am I right? I think an alignment would be a waste of money. Also my car is corner balanced.

Here's a photo of a cat with a hairline crack in the weld bead. It is off of a MB ML 320. The cat is not damaged, that is the inside of same has not come apart, there is no rattling. It's going to be TIG welded tomorrow and I'll reinstall it then. I'm sure that same can be done on a Porsche cat assuming the contents of the cat are not broken.