4. Is it OK to mix other additives to the fuel (like stabilizers and moisture inhibitors)?

We get this question a lot, and I don't really have enough data to support a strong position one way or the other. In responding to the question, I usually offer the following rationale:

1) We have overwhelming evidence in the form of customer feedback to the effect that Marvel Mystery Oil (used by itself) provides all of the great benefits that we talk about so much, including many of the claimed benefits of other additives, like corrosion protection during winter lay-ups, cushioning deposits to soften valve closure, etc. In the face of this history, I've never had any inclination to try to alter what we know works.

2) I have heard of a couple of cases where mixing additives has indeed caused some ill effects in the form of precipitate falling out of the fuel. While these cases involved stabilizer and moisture inhibitor (I don't recall the brand names), rather than Mystery Oil, it was nonetheless sort of a wake up call for me in terms of what can happen when mixing different "medicines" when we don't have any easy way to predict the outcome.

3) Obviously, you can always try mixing different additives in small amounts, and if you get the benefit(s) that you're looking for, without any ill effects, you can continue using the products. I don't know of any case where the ill effects of mixing two additives were so bad that it ruined an engine. - Updated: February 11, 2004