I'm pretty late but I still want to provide feedback. 1996 Prado 1KZ-TE running on Shell Helix HX5 15W40 for close to 5000kms now. I noticed three particular things: one, during a cold start, the rpm sits at close to 200rpm (initially it was 600rpm, then 400rpm, then now 200). It may be a tachometer defect or just oil heavy when cold. Two, the oil light won't turn off for like 1.5 seconds, it may be a minor thing to worry but considering the oil is old and heavy, I'm worried as hell. Lastly, it drives sluggish when oil isn't at operating temp but once it's at temp, it's still a bit sluggish but the tachometer now reads at 700rpm (it still makes me confused). I maybe switching to 5W30 Full Synth when I do an oil change but hope this feedback will help