I went to Castrol Syntec this weekend and I noticed some effects that Ive never had before. First my MPG went ridiculously high to the point where its not even realistic. I read at one point 30MPG, but I was in 6th coasting without any gas just trying to see if I could even get to 30, but still. The average is about 23 to 24 MPG when before it was around 20-21. In two days that doesnt seem realistic. At the same time, contradicting my last statements, it seems like Im burning fuel faster than normal. Like in the 13-15 MPG range. Also I now have a strange rattleing sound inder the Jeep. Sounds like a loose skid plate of something but it seems like its coming from inside the Jeep. This could all be just my imagination but I figured I would ask and see if any of you had this happen.

 

Never heard of this....maybe I should ditch my Royal Purple for Castrol syn??

 

HAHA yea doubt it. I seriously do not think Im really getting as good MPG as the little computer thing is saying. Im going to the gas station today to fill up and do this manually.

 

I switched over to Castrol Syntec at my first oil change, I'm now at 50k miles. I haven't had any of the symptoms you're saying. I did have a rattle at startup, turned out to be a faulty FRAM oil filter. Got a new one and the rattle went away.

 

Forget the digital mpg reading. You said you were doing things to get it to read high. That will mess with the average reading for a while.

Do the miles traveled/gallons burned calculation for a couple of tankfuls to get a more realistic reading.

 

does the noise go away or change with clutch pedal movement(stopped in neutral)

 

Yea I think the MPG thing is my imagination. But yes the noise does go away when the clutch is in. It only made it when the engine had the load. But I have not noticed it today. It was only really loud and "clangy" the other day. I actually forgot about it till I read this again haha.

 

The only strange thing I noticed after switching to synthetic motor oil is increased oil consumption. I do not have any smoke or anything. It actually gives me 1-2 mpg more in city than before. I am averaging 18-19 mpg each tank. But on the other hand, I need to put a quart of synthetic oil every 6 weeks or so. If anybody experiencing this side effect too?

 

I think most of it is your imaagination. That said check your oil filter, you may have a bad anti-drainback valve. I have run royal purple and Castrol Syntec since new on mine with no ill affects or oil burning (6 quarts in 6 quarts out).