TEVE COOK OF TRAVERSE CITY, MI jumped at the chance to buy his mother-in-law's 1987 Cadillac DeVille. A true low-mileage survivor, it was in near pristine condition. Cook was proudly showing it off to a mechanic friend when his friend said "Uh-oh, you bought an HT-4100? Good luck, buddy."

After doing some research, Cook understood what he meant. The HT-4100 was one the most troublesome engines Cadillac ever built. It was known to have an aluminum block with cast iron heads that expand and contract at different rates, causing premature head and intake gasket failure, coolant loss into the coil, and main and rod bearing failure. The HT-4100 also had a heavily loaded distributor gear, weak timing gears and sludging issues.

"My first thought was, if an engine ever needed AMSOIL, it's this one," said Cook. Cook first heard about AMSOIL at the old Broham Dragway in the late 1970s from a fellow racer who swore by it. More recently, Cook spoke with AMSOIL Dealer Dave Mann who made several specific recommendations. Cook also asked around at the Cadillac owners group he belongs to and most of them warned him not to buy AMSOIL.

Having spent more than 25 years in advertising and marketing, Cook skipped the ads and went straight to the science, reading studies done by AMSOIL and independent sources. "I came to the conclusion that it really is an excellent product," said Cook.

Cook initially switched the Cadillac to AMSOIL 5W-30 (ASL), but eventually settled on AMSOIL 10W-30 (ATM). Cook changes the oil every 6 months, usually about 6000 miles, rather than letting it go a full year. "My dad was an auto mechanic and taught the 3000- mile oil change rule like it was the 11th commandment. That kind of conditioning is hard to overcome," said Cook. The DeVille now has 50,000 miles and runs great.

"I have not had a single problem with the 'troublesome' HT-4100 engine. It runs about 10 degrees cooler than with regular petroleum oil, and my gas mileage has increased by 10 percent," said Cook.

"Thanks AMSOIL. By making a superb product that truly does what you say it will do, you've given new life to a sweet old Cadillac, and made a believer out of this devout skeptic,' said Cook.