CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Advantages of synthetic

I was thinking about switching TO synthetic in my 99 Accord. 140,000 miles. Owner’s manual basically says use synthetic if you want to.



I was just wondering if the extra cost could outweigh the advantages, if any.



I currently use Castrol 5W-30 and change it every 3k miles. How often would the synthetic be changed, 5k, 10k?



My inner-conscious says to just leave it alone, advice?



Leave it alone. There is no advantage to using synthetic oil in standard passenger vehicles. You’d be throwing away money.

You’re already changing oil more often than necessary. Your Accord will last a long time. Synthetic won’t lengthen its life. Just keep up with all required maintenance and the car will last as long as possible.

If you decide to switch, DO NOT exceed the manufacturer’s recommended oil change interval. I’m guessing that’s 7,500 miles on your engine, but check the owner’s manual to be sure.

That’s all I need to know. Thanks.

Use synthetic oil if your vehicle “requires” it. Otherwise, it’s just a waste of money.

Your inner-concious is ususally right, and in this case especially. The choice of oil weight, and the 3000 mile interval are exactly right for normal driving.

You should switch to synthetic if:

  1. You are putting very heavy loads on the engine, such as with trailer towing

  2. You are moving to the North Slope of Alaska and have to start the car at -40 regularly

  3. You are planning to drive a fully loaded car across the Southern States and cross the desert at 105F with the A/C on and going 80 mph.

4.You are driving a turbo-charged car

  1. You are driving a car whose manufacturer SPECIFIES synthetic oil.

If none of the above apply, you are wasting money by switching to synthetic, and NO, you cannot extend the drain interval by using synthetic; it was not formulated for that. You would be voiding the engine warranty if you arbitrarily exceeded the manufacturer’s change interval.

Jeff…

I second mcparadise on his advice.

I’ll vary my advice from the others just slightly:

If you notice that you’re burning oil or leaking just the slightest bit, I’d suggest going with a high mileage oil, many of which are synthetics or semi-synthetics… I’ve seen quite a few Toyotas with 2-2.4L four cylinders burn oil past valve stem seals that switching to high mileage oil cured of their ills.

But if you aren’t burning or losing oil, there is absolutely no reason to switch, IMO.

I’m just going to list the advantages of synthetic oil:
-less prone to sludging
-lasts longer in your crankcase than regular oil
-lubricates better under adverse conditions
-flows better in very cold weather
-may give you slight improvement in gas mileage

If you switched to synthetic, you could probably extend your oil changes another 2,000 miles with no harm, but a laboratory oil analysis would be the only way to confirm how much life is left in the oil. I use Mobil-1 synthetic and have been very happy with it. If you feel like trying synthetic, you can always switch back if you feel like it–it will cause no harm.

Since you’ve used conventional oil for the car’s whole life, I’m not sure what benefits you would gain at this point–any engine sludging that was going to occur is probably already done. But there’s no harm in trying if you wish.