<font face=\"Verdana, Arial\" size=\"2\">Why do you change it after every race?</font>
Oil has multiple jobs in an engine:
- Lubrication, to reduce friction between sliding parts
- Hydraulics, to keep rotating parts separated by hydraulic pressure (rod/main bearings)
- Cleaning, to collect and transfer impurities to the filtering system, and to disperse impurities and keep them in suspension until the fluid can be changed
- Cooling, to collect heat and disperse it to the radiators
Oils are designed with specific uses in mind: street, race, low-use, etc. Ferrari, for instance, has Shell (?) design and refine for them oil specifically for their application. We, on the other hand, (well, at least I) don't have the attention of Shell so we have to use an off-the-shelf oil, one designed for the masses and brewed and compromised for a multitude of applications. The chemistry of these retail oils has to take into account uses ranging from your Dad's Oldsmobile that gets driven once every weekend and our 9,000 RPM rotary rockets.
The problem is that as we use the oil, we are constantly affecting its chemistry. As soon as you pour the oil in, it's changing. Its viscosity changes from what it was in the lab, its dispersant and cooling capabilites are changing. Even worse, the process of combustion is adding to the oil hydrocarbons, water, solids, and acids which are quickly breaking down the oil.
For a typical street car that never sees more than 70 mph, never overheats, and gets driven daily in order to burn off the water and some impurities, 3000-7500 mile oil changes are perfectly fine. I have absolutely no problem changing the Mobil 1 in my daily-driver Audi S4 every 5000 miles; I know that the car is treated within a certain parameter of temperatures and pressures and I'm confident that I'm well within the 95-percentile of use that the chemists intended.
However, when I toss that same oil into my street-based race engine, I become concerned. That engine spends the large majority of its life at the top 25% of its RPM range, the temperatures are almost constantly elevated well above what is considered "normal", and the pressures it experiences are always at extremes. I run a fuel that the chemists likely never considered. I drive with others that are dropping wheels off the track, kicking up dirt and dust. Even worse, the engine gets used once, maybe twice, every month, allowing collected solids, hydrocarbons, acids, and water to sit in there unused and undispersed for potentially weeks at a time.
Part of our standard post-race maintenance is to change the oil and filter as soon as practicable to clean out all this stuff and be ready for the next race. It doesn't improve horsepower, it doesn't "insure" anything, but it assures me that I'm using a lubricant that is working at peak designed performance, and I'm confident that it goes a long way to increasing engine longevity.
And at $20 a race, why not? What are you gaining by not changing the oil, other than $20? "If it makes you feel better, I guess go for it."
<font face=\"Verdana, Arial\" size=\"2\">...how do the 24 hours of Lemans racers and pit crew change their oil during the race?</font>
Of course they don't, Dave, because the rules don't allow it, it would be a poor competitive move, and because they engineer the engine to last the distance. However, one thing they do have is someone providing to them a brandy-new $six-figure race engine every race.
Do you?
Greg