Mixing synthetic and conventional oil
 

Due for a couple reasons, but mainly because I was a dumba**, I had to put about a quart of conventional oil to top off after an oil change. Do I need to redo the oil change with all synthetic ASAP or just leave it until the next change? I had to remove the filter after the change and saw the oil had already become dirty just driving down the driveway. I know it's not due to mixing synthetic and conventional oil, but wondering why it would be dirty so quickly.

I also noticed I was about a quart low since the last change. Dipstick was below the xxx zone. I was hearing rattling sounds right after startup, but I thought it was just due to cold engine. Hope I didn't do permanent damage.

I did this once driving back from Key West to orlando. Pulled over at the very beginning of my trip for gas and decided to check the oil. I was a quart low and all that was around was synthetic. I did it since it was my only choice. Car seemed to drie a little smoother since the synthetic was probably a little "slipperier" oil. When I got home, I just changed the oil back to regular. Car was fine after that. The job of oil it to lubricate internal parts so you don't have wear on friction points and ALSO particles inside the motor to stick to the oil instead of collecting in places. I would just change out the oil whenever you first get a chance and keep an eye out after that.

Thanks Somthnfrce. My main concern is that my engine requires synthetic and I put in conventional, albeit only a portion. Sounds like yours didn't require synthetic so using synthetic would be purely a matter of choice. I also read something that synthetic and conventional don't mix (as in becoming one liquid) so wherever synthetic is, the conventional oil can't get to it. Don't know how much truthiness there is in that random web site. In the bottled blends, it's usually a very small percentage synthetic and mostly conventional, as a market ploy to sell more expensive oil.

There is no problem mixing the two. In fact............that is what "semi-synthetic" is all about. Semi-synthetic is a waste of money............synthetic is worth every cent that is charged. When your next oil change is due, change out to your synthetic and you will be fine. The fact that your engine is now "rattling" has nothing to do with one quart of 'regular' oil being mixed with synthetic.

r.

You can run conventional....you just need to change it every 3,000miles or every 6months...
Synthetic every 5,000miles or every 6months....

just make sure your using the proper grade or wieght, and you'll be fine.

That's interesting... Valvoline told me the synthetic I used was rated for 12000 miles!

Go right ahead and travel 12,000 miles............at your risk. Sure, BMW indicates that many miles on their Castrol made product (which is formulated to BMW's standards). One of the reasons is that BMW and other European mfg's have "free" service and so it is a cost savings for them. Of course the "free" service is only for the warranty period and so if you purchase the auto used............then you may experience issues. At any rate it is the filter that helps in the longivity of the engine and so you will most generally find that a 'factory' filter is superior to the aftermarket brands. Look for the valve on the bottom of the filter...........if one is not there............as in most aftermarket filters.......then you have a 'dry' start up. the valve keeps the oil from draining back to the pan from the oil galleries. Lastly, I use BMW synthetic oil in all my autos (5) one of which is a 1965 Austin Healy........... which many say will cause oil leaks. I have yet to experience any.

r.

Both oils had the same weight so I'm going to let it go until the next oil change. I also found it interesting that before the free scheduled maintenance deals, manufactureres recommended 3-5000 mile oil changes. Then after the free maintenance it went to 7500+ miles.

No, I didn't say the rattling was related to mixing oils. I thought it was related to low oil or cold engine. It seems to be reduced now with proper oil level. Oil light never did come on or I would've added some.

Synthetic OIL Does not cause Oil Leaks! In Older cars where seals are worn out in the motor, it simply finds the worn out spots and leaks at those pressure points!

True. I have used exclusively synthetic since the early 70's when Mobil made it available to the market.

r.

everyone here has made very good points and i wanna add to that.

i have heard that mixing different oils may produce chemical reactions due to the different chemicals that maybe used. these reactions may end up breakign the oil down faster or making some kind of corrosion. have i ever seen proof of that nah.

second thing, oil is supposed to lubricate and keep the inside of your engine clean, it only does that when it's at it's operating temperture. let your engines warm up, expand to it's tolerances and cook off that condensation inside before you drive off. you'll have less of a chance of spinning a bearing or making piston slap.

theres tons more i can say about this, but i'll spare you ;P