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Oil doesn't wear out, break down, or burn up to the point of losing lubrication ability, oil simply gets dirty. Conventional oil has the downfall of the being a refined substance, which means there will be impurities here and there and also some substances that optimally wouldn't be there to begin with, such as chemicals that will deposit sludge after a certain point. Synthetic oils has many benefits and really no downfalls when comparing it to conventional oil. It has fewer contaminants, cleans better, and has a lower coefficient of friction. I wouldn't recommend the change to synthetic with a high mileage engine, if anything you could buy a dedicated high mileage oil such as that from Quaker State. Synthetic and conventional oils don't mix, you optimally want to clean out crankcase sludge prior to changing over anyway preferably. Anyway, conventional oils will do just fine, while synthetics are better, it won't mean your engine will fail prematurely either, I've had plenty of cars roll past 200-300k without mechanical problems such as bearings, cam lobes, etc. wearing out, or having excessive ring wear for that matter, and all used conventional oil. Conventional simply requires more frequent changing intervals.

But still, a well maintained vehicle does wear over time. Bearing get looser, piston rings arent as snug, valve seals arent as tight. If the car has over 100,000 miles i wouldnt bother. I would stick w/ regular oil.

TEDD

But some engines, especially those that have been driven and maintained well, might not have leaks. And even if they have been using traditional petroleum, a switch to synthetic will probably significantly improve efficiency and longevity.

The problem is I do not know if there have been sealed up leaks in my engine. I guess there is no way to find out unless a synthetic is used...

Thanks for your input.

Synthetic is far superior, but not necessarily on older engines. Synthetic can actually be worse in older engines w/ tons of wear. Synthetic tends to be thinner and can actually burn more synthetic than regular oil. Unless the "older" car just had an engine rebuild, i wouldnt reccomend synthetic oil. I would stick w/ conventional oil.

TEDD

I've heard and read that synthetic motor oils, when used in older and high-mile engines that have been servciced with traditional petroleum oils, can clean out the "sludge" that seals leaks in the gaskets/etc. This will be, obviously, a very money and time consuming repair job.

But I've also heard and read that not ALL older engines which have been switched from petroleum to synthetics experience this. Of course, this would be the optimal solution since by switching to a quality synthetic oil, along with quality oil and air filtration systems, I will only need to replace the motor oil about once a year, thereby saving lots of time and money.

So does anyone want to persuade me to take the risk and switch to a synthetic?

Considering these brands:

AMSOIL
Neo
Schaeffer
Red Line
Mobil 1