Should I be using synthetic oil in my 2003 VW Passat GL 1.8T sedan? The dealer says I should, but the Oil Sludge FAQ sheet I received implies that engine oil sludge occurs primarily when the engine is operated at oil change intervals beyond those prescribed in the manual and that the decision is up to the vehicle owner. The car has just under 50,000 miles and the oil has been changed every 3,000 miles. Thank you.
You can change the oil at 5000 intervals however due to the VW xxx spec it REQUIRES synthetic.
The 1.8t has a design flaw that makes it harder on engine oil due to a smaller oil sump in the Passat/Audi since its longitudinally installed(crankshaft runs front-back). The Golf/Jetta/GTI/Beetle(crankshaft runs passenger to driver side of car) with the exact motor but different oil sump do not encounter this problem as easily.
The VW oil spec for your car is 502 which is synthetic oil only .
There are many many types of oils for cars. There are many that are synthetic and many are not. Car manufacturers test their cars with oils meeting certain specifications and then provide that information to you in the owner’s manual. In your case I believe VW list it as a “500” number. This is unique to VW. Most cars use the S(letter) like SF classifications (Version F of the SAE oil specs for Spark (gasoline) cars).
You need to use that have that 501 (I believe it is 501) VW specification on the can. I believe all oils meeting those specifications are synthetic, but it may be possible that some are not.
If you choose to use an oil that does not list that 501 number, or whatever is listing in your manual, then you are risking damage of various kinds including sludge.
Don't rely on the lube place or even a dealer to give you the right oil. Check the container yourself. Getting oil that meets the specifications is your job.
I see that you may need 502 oil. I suspect genex is correct. but check you book just in case. You can substitute 502 for 501 safely. Generally, but not guaranteed, you can usually substitute a higher number in that series.
Also, you do not need to change the oil more often than recommended in the owner’s manual. It will not help. However make sure you are not using your car under severe conditions.
It has been found that under some conditions changing oil more often can actually cause more damage than changing it at the scheduled time, although it is very small.