My motor is a 2002 Toyota Avensis Estate GS 1.8 VVTI with 113 000 miles on clock . Being the infamous vvti engine it hasn't until recently done too badly but now I'm putting in a litre of oil every
800 - 1000 miles . I've been using Halfords 10 w - 40 semi synthet. but wondered if it would be advantageous to switch to a ' higher mileage oil ' e.g Castrol GTX High mileage oil ? Anybody here used this with good results etc. ? I understand it is a mineral based oil so is it OK to add to existing oil or do I need a complete oil change ? Is there any adavantage to sticking with semi synthetic oil or as I am topping up so regularly would the cheaper mineral oils be OK to use ?Thanks for any help