I recently switched to Mobil 1, and it's still in a "cleaning" mode in my engine.

I know guys use a little ATF mixed with conventional to clean deposits before switching to full synthetic.

Since my valve seals leak, I have to add oil occasionally (I will be replacing them soon). Instead of pouring Mobil 1 in there at this early stage, could I just top it off with a little ATF and save a few bucks?

the question is: is there any reason i shouldn't combine these two fluids?

thanks.

 

what weight oil is the mobil 1? I would say if its thick enough a little atf probably wont hurt. I have a 7.25 quart capacity in my setup and have added up to a 1/2 quart of atf with positive results. Less lifter tick on startup was one thing i noticed.

 

It's a heck of a waste of expensive oil... You're not going to be in cleaning mode for 5000 miles are you? (I hope not...).
It's not going to hurt anything, you're just going to be draining and throwing away your pricey mobil one that much sooner.

 

Depending upon exactly which Mobil 1, it is probably as good a cleaner as petroleum ATF.

Back in the early days of synthetic oil, a common "cleaning" practice was to use one quart of synthetic the rest petroleum at the first oil change; next change, 2 quarts synthetic the rest petroleum; third change, 3 quarts synthetic the rest petroleum, etc.; until you got to a complete synthetic change. Changing the filter with each oil change, of course. To me, that makes more sense than using ATF, which isn't a motor oil. But, a lot of people have gone the ATF route without harm.

AMSOIL recommended the "one more quart of synthetic with each change" approach until they introduced their crankcase flush in 1982 or '83 (forget which, exactly). The flush is certainly cheaper than partial synthetic changes over 12k miles.