Hi: I've been driving land rovers since 1973. I use land rover recommended viscosity oil. I've been using Amsoil 100% synthetic oil since 1974. It gives you more power, keeps engine clean like new inside. I started with a new L88 (defender type) 4 cyl, no AC, dual safari roof, and when it got wet, I had a crank to start the beast. A 1999 discovery II for 15 years, 09 RR sport HSE and now a 2016 LR4 HSE Lux. I do most of the maintenance, oil changes, expansion tank replacement, cooling systems, brakes. Amsoil the original synthetic oil manufacturer from Wisconsin, suggest to change oil every 25K miles. I change oil every 20K miles and filters every 10K miles. I use K&N reusable air filters, they last for the life of the car. But I am looking forwards to get me a 2021 Grenadier, since the real Defender was replaced by an expen$ive, elegant wagon with a defender name on the bonnet. If you maintain a Land Rover properly, it will last for a very long time. I live in Utah now.