Product is a solvent based product that is best suited for use in the fuel. They claim that it can be used for internal oiling system cleansing, however it will severely dilute the viscosity of your oil. We at Auto-Rx never recommend putting old school solvent flushes into the motors oiling system, because many times it will release chunks of hardened contaminants that can do real harm to the engine internal. These solvent flushes can sometimes adversely effect engine seals, leading to aggravating drips. The best attribute to these solvent flush type products is that they are very inexpensive.
A good rule of thumb is to never put more than 1 additive into your oil at any time. So absolutely do not run Auto-Rx and Seafoam in the engine oil at the same time. I would say that your motor is acting normal with the change over to a 5w 40 motor oil. This is providing a thicker oil film to help keep the oil pressure up. This is a logical move to make on a motor with high mileage or age, where some mechanical wear has occurred. You will likely get some cleaning benefits from the diesel oil, as they are loaded up with more detergent/dispersants than regular oil designed for gasoline motors like yours.
I would be very hesitant to put solvent chemistry into the current motor oil. This will likely dilute the 5W40 down to the viscocity of the 5W20 that you used to use. In essence you will be right back to where you started.
There is some good information on the Auto-Rx site comparing Auto-Rx to solvent flush type products. It would be well worth the read.
