I got a 2000 Toyota Sienna a couple of months ago, it has 181K miles and I suspect much of that is on the highway as there are a fair amount of rock chips on the hood paint and only slight wear on the brake pedal and drivers seat. It runs and shifts great, holds all its fluids, recently had a timing belt changed at the dealership about 15K miles ago, and is still in fantastic condition overall for its age both inside and out, so I really want to try my best to keep it forever.
When I looked in the engine under the oil cap I saw a thin layer of sludge with a few clean spots here and there so it didn't seem too bad, however should I still consider doing a motor flush or using marvel mystery oil with my next oil change just to be safe with this somewhat notorious 1MZ-FE engine? Also, it had a 5w-20 oil change just before my purchase, but it specifies 5w-30 on the cap though so I was wondering not only if I can safely use 5w-20 living on the Texas coast, but also if continuing to run the slightly thinner synthetic oil might even be beneficial for keeping the sludge at bay in this engine?
I would not worry too much about the sludge unless it affects the engine performance.
To be safe, just use quality oil and change the oil and filter frequently. Your engine is old and flushing with harsh chemicals (oil cleaners) might result in more issues. Also, stick to the recommended oil viscosity.
@yaser Thanks for the reply, so you're saying MMO would be too harsh also?
It should be fine as long as you follow the instruction, but to be honest, since you don't have issues, as long as you change the oil and filter frequently, you are fine.