Does anyone know if using a fuel injector cleaner, like STP, will dilute the oil already running in the car? I was told that you should only use the cleaner just before an oil change, so as not to have the diluted oil in the car.
The real reasoning behind this has nothing to do with fuel dilution. Fuel system cleaners are primarily supposed to remove dirt and carbon. Some of that will inevitably end up in the oil, making it dirtier. This is why you should run a cleaner on the last tank of gas before a scheduled oil change.
That's the same question I've had for a while now. The answers I got is that it does affect the oil in some fashion shown on a UOA, but nobody has commented on exactly how it shows up.
I've noticed that with regular use of these products, my oil appears to "bubble" on the dipstick similar to if the dipstick was dipped in water before measuring the oil level. It has the appearance of "repelling" away from the dipstick. The products seem to "thin" the oil out a bit, but that's just my speculation. Haven't figured out if it increases oil consumption.
The problem I have with the useage recommendation is it refers to the concentrated fuel system cleaners, but there are gas treatment products (eg. STP) that I use at every fillup (ala Fuel power) and there is no way to 'flush' them out of the oil.
I've never seen any difference in the oil when using a FI cleaner. I had my injectors cleaned professionally after using several bottles of stuff and my last UOA came back normal. I think most of the crap goes out the exhaust unless you have a worn out engine.
I've been using AMSOIL PI for many years, and have never seen anything in oil analysis that indicates that. Of course, at 1 oz per 10 gal of gas, there isn't a very high concentration to begin with. Even with relatively high blow-by, don't think there would be much noticeable.