Questions about oil changes

[ncyrider]

Did an oil change on my '01 ST the other day, and since it's about to hit 100k miles, I was wondering if it would be better to start using synthetic oil the next oil change. I've been using Castrol GTX oil and Royal Purple oil filters on this truck since owning it, and I know that GTX is probably just fine to keep using. But when these Explorers get to over 100k miles, is it good to switch to synthetic or "high mileage" oil? Either way I will keep the oil change intervals every 4500-5000 miles.
Also, there was oil residue under the oil drain bolt, on the oil pan, and on the oil filter. Noticed this a couple months ago, but I don't think it was enough to ever drip any oil down. But I don't remember ever seeing any noticeable amount of oil residue in the past, so that's why this came to my attention. I might have forgotten to wipe off the oil filter mounting surface during the last oil change several months ago, so I'm guessing that's why residue was all over the oil filter. And I have also never replaced the drain bolt's orange o-ring/gasket, so I'm guessing that would explain the residue on the oil pan? How often should that rubber gasket be replaced?
The oil level was never low on my ST. Anything else I should check or replace let me know.

 

[ptf18]

I've got 70k on the replacement engine in my wifes 02. My 02 Ranger Edge has 176K on it. I dont plan on changing to any other type of oil than what I've used since either of these vehicles were purchased new (in '02). Motorcraft oil and filters.

As for your oil leak... I'ld look farther. Doubt its the plug. the 4.0l engines were known to leak oil from the valve cover and on some engines (like mine is) from the oil filter mount (to engine block)

 

[sr139fox]

I run synthetic oil. 188,000 miles. Just the chain rattle at start up. I changed both valve gaskets and oil pan gasket. New drain plug. No oil leaks. I heard the synthetic oil will leak more then regular oil. Dave P.

 

[ptf18]

sr139fox. I'd replace both tensioners if your hearing the dreaded chain rattle at start up. You might try holding the throttle pedal down while you crank the engine for I think its 10 seconds. And then light off the engine. I've read that this method will prevent the engine from starting but allows oil pressure to build up prior to light off as to pressurize the tensioners.

Search the forum about this method.

 

[Paul Fithian]

Not based on time.

Watch the oil pressure idiot gauge. Lift your foot off of the accelerator when it jumps to the middle, indicating oil in the engine is pressurized.