Originally posted by: Exterous
I have a '98 ford Taurus with 250,000 miles on it (123,500 on this engine) and I was wondering if high mileage oil is something worth putting in instead of the standard?
High mileage oils generally are higher in the cSt department than the other oils in their @100C viscosity class. What this means is if you take say a regular dino 5W or 10W-30, it'll have a cSt @100C in the high 9.9's or low to mid 10. If you go take a High Mileage 5W or 10W-30, it's cSt is going to be right at the top of the 30 weight range...most likely 12.something cSt @100C. Many/Most/All (it's not 100% known) of the High Mileage oils will probably have some additional seal swell adds in them to swell your seals to help stop leaking/oil consumption. The also will probably have small % of a PAO in them, which is a good thing as that's true synthetic (Group IV).
In general, except for the fuel mileage hit (whatever that is) by running a higher viscosity oil compared to just a regular dino, using High Mileage oils even in newer engines would be fine, and in some cases, maybe even preferable.
As far as synthetics causing leaks: This is generally because the engine has been on a diet of dino oil, and most likely not have had the OCI kept like it should (i.e. too far on the oil). So what happens is that the seals start to get degraded/dry, and sludge builds up. The sludge actually acts as a false seal. Then someone decides to put the synthetic in, which not only flows better than the dino*, and in many cases has more detergency, and Whamo, you get the 'Synthetic causes leaks' thing.
*Flows better is accurate. Commonly you see the 'Synthetic is thinner' comments. This is not the case. If you look at the @100C cSt values for synthetics, they are right in line and sometimes even higher than the dino's they replace. Synthetic flows better, it may or may not be thinner...that's totally dependent on which two oils are being compared.
As far as putting synthetic in your ride:
Even if you did a steady diet of proper OCI's, your engine will have sludge, and the ring packs will be sludged up. If you actually want to clean the engine out (for the oil system out at least), then before going to synthetic, you should do an Auto-RX regime first. Then, once you've completed that, you can go to synthetic and not look back. The bennie there is that the gas mileage bump you'll get will end up saving you some real $$ depending on the miles you drive... You can check Auto-RX out at
BobIsTheOilGuy.com Forums, go to the Oil Adds forum.
Hope this helps...
Chuck
P.S. I'm not affiliated with Auto-RX in any way, just another one of the very satisfied users...