Well by your comment. It seems that I come from Maaaaarsss and know nothing about your world and pk in this world........................
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I am maintaining a fleet of more than 1500 vehicles of all types consisting. Merc May bach to this little JDM vitz which is so much sensitive as you see it.............. the intervals I had mentioned are tested safe with this tooooooooo expensiveeeee jamaneeeessss tokonolgy... and it work likes charm on this little machine.......
And alll of you guys who follow the boooook for oil recommendation Should burn alll of the research papers about heat and viscosity index............. any thing from -20 to -30 is suitable for a temperature range of upto 20 C. It collapses on further increased temperatures........
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Just see the temperature in your city amd choose the viscosity.
Other wise this pakwheel form is full of crying peaoples whose engine smokes whitish bluish at part or full throttle loads........
Once again its your choice to follow the book recommendation of some region whose year round temperatures are stabled at 25 C. And destroy your vehicles engine or be a sensible man and follow the heat index chart to avoid the hassles you will face after a season or 2 by using these low visc oils and there after math consequences.
One thing more I will share with you guys low viscosity oils like 0-20 5-20 5-30. Doesnt protect your vehicle engine ilfrom extreme internal heat generated by your engine. Thus the thermal efficiency drops down and the results are faster wornout of your vehicle engine parts. One common problem now a days I am facing in islamabad about vitz 1kr-fe and 2sz-fe are engine oil pump failure due to the continous usage of these oils in extreme summers.........
If you dont believe it dont do it and just wait for your personal experience about a little bang.....
Goood luck.