Running a dino oil during break in makes sense. Dino engines are supposed to be looser than synthetic engines due to the lesser lubrication. During the break in period you're trying to loosen up the fit so it makes sense to run the dino oil until the desired fit is achieved, then the switch to synthetic is made. The same result would be attained with running full synthetics from day one but I'm sure that it would take much longer.

Castrol Syntec.

The synthetic oils reduce friction better than standard oil because the synthetic molecules are smaller. Cooler engines run better, with better horsepower and improved gas mileage. They suspend dirt and water better as well.

I don't run anything else in my '75. Only 4k on the powertrain and I plan on keeping it like new, too.

tc

ps - Most standard oils are the same, but the addatives that are utilized to suspend water ARE different. Don't ever mix brands or sludge will develop.

Ok, noticed something in here about 'blended' oils, mostly 'dino' with a percentage of synthetic. What kind of harm would be done by putting in 4 quarts of 'dino' and 1 quart of 100% synthetic (all the same viscosity and from the same brand)?

** 6/16/2003 ********************
Still wondering about this, any comments?

____________________________________

Jim O.
Save the Wave...!!!

|UPDATED|6/16/2003 1:15:42 PM|/UPDATED|

After an initial break-in of 10K miles, I started using Mobil 1 in my GrandCherokee. My last oil change I tried Havoline fully synthetic. It was $2 cheaper than M1 and the performance codes on the back of the bottle were the same. I'll check gas mileage at next oil change to see if there is any difference between the M1 and Havoline.
The white princess gets 10W-30 with a purolator filter.
Since I only drive about 3K/year and the oil gets changed at least twice, synthetics get to expensive. Also, the quality of the oil today compared to 30 years ago has increased dramatically. Any major brand oil should work just fine.