I would not put synthetic oil into a 1990 300e..believe me not good...you will see why shortly I bet...just put the what the owners manual says...really...save you alot of trouble down the proverbial road.....

 

A few facts on motor oil based on oil samples from years and many diffrent style motors, not my daddy ran this so I do. Most all oils today use a pure stock base as it stands heat well. Older oils had used parifin base stock with heat left a wax build up. The biggest difference is the addittives in the oil both regular and synthetic. The biggest reason to change oil is dirt in it. You can change the filter every 3k miles and once you add 1 qt of [quality] oil it has all of the additives needed. Oil basically doesn't wear out the additives do. Now on synthetic's you can run longer, but suggest changing the filter at normal entervals oil every other. Cold climates it is great were reg oil will bypass your filter until warm. Always make sure the oil spec's meet or beat what your engines needs. Mobil 1 is a great oil but does not meet diesel engine spec's in shear strengh/ hard on bearings from high compression. Engines will always make oil dirty from combustion. Synthetics work best in non combustion area's so extended entervals are fine. CLIFF synthetics are not crap! Also the additives to make 5w-?? wear out faster than a 15w-?? This is from a lab that blends oils and tests them

 

no, i must disagree again..if the manual doesn't call for synthetic oil do not use it...if it (the manual) does call for synthetic then fine, by all means, use it. I would never suggest putting synthetic in a non-synthetic recommended engine any more than vise versa...just that simple

 

Interesting posts, thank-you gentlemen