I recently just purchased a used 04 6mt coupe. The used G was not at an infiniti dealership so they had no idea of the prior vehicle maintenance history. They wanted to do an oil change before I received the car. A friend of mine works at this dealership so I got a good deal on the car and she also really wanted to help me out since I actually live in Germany.
Well after reading through the vehicle history from the previous owner....it looks like at approximate 10000 miles he switched to synthetic oil. Well...I know they did not put synthetic oil in the car when they did the oil change. This oil has been in the car for about 2 months now since its been on the boat being shipped here to Germany. I've been trying to do some searches and I find many comparisons between the 2 but nothing about the pros and cons of switching back to regular oil. Maybe this is an unwritten rule that once you change to synthetics you don't want to go back...but...I don't know for sure. I've heard it but, why...and is this even true? I appreciate any advice ASAP. Its the weekend and if its critical to do a change I will now but, if not I'll just wait. Thanks.

 

you can go back with out any problems. I always switch to synthetic after 7500 miles or so and normally do oil changes at 5k. (i do a lot of highway driving, not much stop and go). I also send a sample of my oil to Blackstone labs for testing with each oil change (they only charege 20 dollars). I have done this on my 2000 maxima my 2002 maxima my 2004 g35 6mt and will do it when i get 7500 miles on my 2005 6mt. They compare your wear numbers to all nissan engines of the same series that they have done and give you detailed anaylsis of all the componetes they find in the oil. On all of my cars I have always had lower amounts of contaminates and metals in the oil i have had tested then the average for these engines even though most change their oil well before 5k.

 

if your going to change from syn, semi syn, regular always make sure you do a complete drain and change the filter.. do not mix the three together in large amounts. other then that do whatever you want, i wond suggest syn after 20,000miles

 

So the saying that once you go synthetic...you don't want to go back...is that just BS? Are there any facts of why you wouldn't want to go back to regular oil once you go synthetic? So what you are saying is that its ok. Thats good to know...I guess I just hear alot of the latter and I'm hoping someone can clear it up as to why this would be true or why its just a misconception.

 

think of it this way..

they suggest NOT using syn oil because syn is "smoother" then regular oil. You'll want to use "rougher" oil (Regular) for the first few thousand miles to.. lets say "sand down" or wear down your new parts in the engine. During your first few hundred the parts in you engine will give off some metal flakes.. some are noticable others are not. This is also the time for your rings to seal. That process is called "Break-In" thats why you see people post up questions like "HOW TO BREAK-IN?" and ask about first oil change etc..

anyways, usually around 1-5,000 miles people will change to syn. I wouldnt recommend syn until 10-15,000 though. But you can use regular oil or semi-syn or full syn.. whatever you want.. just change your oil every 2,500-3,000 miles.

edit:
if you are planning to do any future oil changes yourself.. heh heh ._. its a pain in the ***
you'll need to jack up the passenger side..
10mm socket, and 14? or 15mm wrench
5 quarts of whatever oil as long as its 5w-30 or 10w-30..

 

i have 55k miles on my g35c...would u suggest synthetic or regular? i was planning on putting the synthetic in next week. i dont know what was used before...as i bought the car used with a bunch of miles.

 

what about that new Q oil

 

i dont know about the Q oil but everyone in my family has been using Mobil1 Full Syn Motor Oil as syn oil since i can remember. Costco has a great deal on them but they dont always carry Mobil1 so if you guys are costco members go check out the section every once in a while.

Asztk01: I would use syn its easyer on your motor

btw syn does cost more then regular

 

20 years ago, it was possible to get some foaming when switching back and forth between dino and syn. Now days, they are compatible and this will not happen. 20 years ago, the seals were made from material that would swell alittle with syn. Switching back would cause leaks. Now days, seal material is much more advanced and syn is formulated to not affect seals.

Going to syn in a high mileage car is not recommended because syn may loosen any sludge that has built up. Most syn is high detergent. Now, a properly maintained car with dino shouldnt have any, so its a case by case thing. But that is the reason behind it.

 

btw, the FAQ on the mobil1 site addresses your questions directly.