My wife's CRV is the vehicle in question and it pertains to the MM.

Her vehicle requires a full synthetic which I adhere to. Now I know the MM doesn't "test" the oil and the life is based on time, starts, etc. But being that synthetic oil lasts longer, would we not be wasting our money is we go simply according to the MM?

I recently changed her oil at 15% and think I may have done it prematurely. Thoughts?

 

damn good question. been wondering this too myself after switching to synthetic. was wondering why my MM went down quickly with Royal Purple. When i changed it oil it was really dark compared to the new oil I put in. maybe the MM is smarter than we think it is. RP isn't meant to run long mileage. I guess I'll see when I change my Pennzoil Platinum how the oil looks like at 15%

 

I only use Mobil1 green cap on my Fits. I let it go to 0% before I do the change. One time I was under by like 500miles.

 

I think people generally change their oil too frequently. If you live in the city, you gotta change it though. I do little mileage and my engine sounds noticeably less smooth at 10% oil life. Quality engine oils have detergents in them to clean carbon deposits so a dark oil usually means it's really doing its job and doesn't mean the oil is bad/used/degraded. Even dark oil could still have life left in it.

 

The only way to reliably answer your question would be to send off for an oil analysis when the maintenance minder says to change the oil. Based on what I've seen reported here from people who have done this, it's pretty accurate but a little on the conservative side—i.e. you could go somewhat longer than it says, but only maybe 10% or 15% more, not enough to save a vast amount of money.

I suppose if you were in charge of a fleet of Fits it might start adding up to useful savings...but for a personal car, a couple of oil changes over its life hardly seems worth worrying about.

 

If your car specifies synthetic, your car's MM assumes you have synthetic- so synthetic won't last "longer" than the MM's math.

Honda being Honda, I take it as a given that the MM is very conservative. But I like having my trip odometer instead of an oil change nastygram, so I change it not too long after it starts pestering me. I just hit 36k and only had to do my third oil change recently, so I don't think I'm wasting much money.

 

A more scientific way to tell when your oil is getting 'used up' is to have it analyzed by a chemist. I couldn't tell you what substances you need to check nor can I tell you what the numbers should look like. If you want to get into this, there's a great website at BobIsTheOilGuy.com where you'll find lots of expertise.

IIRC, based on chemical analysis, one can get even more life out of synthetics by simply adding a quart of new oil (draining a quart as needed) to restore the critical additives - assuming you don't have too much dirt in there.

In a more practical sense, I use synthetic but change per the MM but don't feel like its a waste. My change intervals are much longer than 3000K and I don't have to worry about getting the oil changes out of synch with the MM and managing them manually so it's more about convenience for me. DIY oil changes with synthetic are the same cost as JiffyLube or any place else I'd go to have someone else change it. Also, I change at 0% or slightly longer.

I suspect our cars would do just fine with good quality dino oil and mid-priced filters but synthetic has the added advantages of less coking on over-heating, less sludging on many short short trips (no engine warm up), and more detergents keeping the engine cleaner. None of these are factors if your engine is in spec (not overheating), you maintain the engine (air filter mostly) and you drive normally (good mix of short and long trips so water doesn't collect in the oil).

 

Well shit. Why didn't I think of that? You are right.