what engine oil is recommended for Toyota Highlander 4WD?

AJ the actual weight of the oil is not as important as the quality of the oil and how often you change it. This vintage highlander is among the Toyota who are suspectable to problems as the result of a pretty nasty sludge build up problem in the engine. Sylube (http://www.synlube.com/sludge.htm) will try to sell you some oil on this site but they take on the issue in more depth than you are probably prepared for (or interested in) Here's a site outlining the problem and Toyota's response ... http://www.yotarepair.com/Sludge_Zone.html And here is another forum thread on the subject ... http://www.toyotanation.com/forum/archive/topic/113928-1.html Hope that helps! Good luck....