My email to AMSOIL
"I have 2 cars- 1991 Ford Tempo 2.3L HSC 4cyl Automatic with only 20,000 miles, 8,000 which were in the last 6 months. Which oil should I use? I don't know the condition of the seals, but the car was barely driven at all, though it doesn't seem to have any leaks. 1988 Mazda MX-6 GT (turbo) 5 spd, 140,000 miles. No apparent leaks. Previous owner claims 3,000 mile oil changes. Both cars were 1-owner cars. I'd like to switch both to Amsoil synthetic if it's recommended. I'm considering the bypass filter for the Tempo. Any suggestions- motor oil, transmission oil, or other fluids would be greatly appreciated. One question I've received is in regards to synthetic oil being thinner than conventional oil. Is that true, or in what sense could that be true?"

Their response
"Our AMSOIL Synthetic 10W30 Motor Oil (ATM) can cover both applications nicely. The Tempo can use our AMSOIL Synthetic Universal Automatic Transmission Fluid (ATF). The Mazda transmission may use the ATF also, but some use gear lube and the lube guide isn’t crystal clear as to how to tell which is which. You may have to check with the dealer on this one.

The correct AMSOIL dual remote bypass kit for the Tempo is the BMK13. It comes complete except for the filters themselves. Because of the broad use of this kit we recommend filters based on the capacity of the engine’s oil sump. For this size capacity we recommend our AMSOIL SDF15 full flow filter and the BE90 bypass filter.

We certainly understand the initial reaction of those who are surprised at the consistency of synthetic lubricants. Outwardly they do seem “thin” in comparison. All petroleum oil has a certain look and pour rate that we are all familiar with. The molecular structure of synthetic oil is such that the pour characteristics are much superior and makes them appear thin, but actually the high temperature protective film strength is many times higher than petroleum. It does take some getting used to."