Alright just picked up my very first XJ today, its a 1999 with 125k on the clock and I am about to do its first oil change (since its been in my possession) tomorrow afternoon. I have been told time and time again that if an engine has been run with conventional oil its entire life that you should keep using it and never switch off to Synthetic, I heard that since seals get used to conventional oils that when you switch to Synthetic it cuts their life span down dramatically, is this just an old wives tale or is there actual truth to it? Thank you in advance for any and all help you can give me.

 

Yes and no. Synthetic oil will not cause your seals to fail. It can however clean any sludge around the seals/gaskets that are hiding a leak.

 

Never heard of that. I just use 10-30 in the winter and 10-40 in the summer. Why spend all that extra $ for nothing. I've never had a problem not using synthetic! Cars lasted for decades and decades before synthetic and will continue to do so. When's the last time you heard of a 4.0 blowing because they didn't use synthetic? These motors will last hundreds of thousands of miles with the tried and true.

 

Synthetic oil is a much better detergent than dino oil. The same could be said about oil additives, MMO, lucas, etc. They don't cause leaks but they can bring leaks back that have been blocked oil sludge.

 

Google "oil myths" and get the facts.....

I believe the results in that pic are from pure owner neglect.......any oil, syn or conv, will look like that when left in too long.

 

Synthetic is fine. It just doesn't make economic sense, IMHO since you should still change the oil on the same "dino oil" schedule, and conventional oils do just fine on that schedule.

 

Filter choice is much more important. Use Wix, Napa, Mopar for example. They're known quality filters.

Shine a light into the oil filler hole and gander at the conditions inside for yourself.

 

That looks like my aunts old engine before I did her head gasket and cleaned it lol