Vitz 2011 sudden drop in fuel average

[pwuser151563994363]

Bought used vitz 2011 model 2015 import, 2 months ago from a known person and ODO was 58k (genuine) the car was totally fine mechanically speaking. The previous owner was using 0w-30 and since odo was 58k it was not suitable anymore and I discussed with some good mechanics and oil experts. The car was giving me 15-16-17 without AC Here's what I did with car in the order:
1. Catalytic cleaned.
2. Tuning and overall checkup from toyota
3. CVT oil changed from toyota

Then after sometime I changed the oil to 5w-30 I use Micking

I get petrol filled with hi octane always (mixed)

After oil change too everything was fine and I was easily having 16-17 without ac and 14-15 with AC (Alhamdulillah)

but last week I went to Multan vai motorway and came back the car gave me 12km/L with AC and 120km/h but THE MAIN ISSUE IS, Since I came back the car with or without AC is not giving me more than 12km/L and the reading too and manual method too. I changed the plugs, had throttle body and tuning done too but still I'm not getting more than 12. The AIr filter is clean too.

What could be the reason?

[ktech786]

@rajaatta raja sahib ,classic case of negligence of Patla hail not suitable any more.gaara add Karo.
A myth and disaster ,you are always trying to prevent ,but ustaads win...

[pwuser151563994363]

That's what I thought that the thick oil was reason but 2 fuel tanks with new oil still gave me best average. What do you suggest though? should I change back to 0w-30?

[rajaatta]

I no more recommend people to use low viscosity oils because let them we experience themselves. I am now diverted to rebuilds more often then banging my head on low viscosity index oil explanation to people here on forums. Let them use the oil and when their engines got damaged they would understand the importance then.
Thanks for mentioning but brother it's of no use now.

[talhamaqsoodch]

Check your car manual, most probably it will suggest 0W20, it doesn't matter how much your car is driven use only recommended oil mentioned in manual.

[Salmaanawan]

The previous owner was using 0w-30 and since odo was 58k it was not suitable anymore

How did you come up to this conclusion? I don't blame you, its a famous advice given to people by our ustaads. But to be honest, you are to blame aswell. You have access to internet and the worlds knowledge, why would you trust an ustaad?
Anyways, we have a 2001 city sx8 at home. From the very first day we have only used 5w30 oil in it despite the fact that many ustaads have told us to switch to 20w50, but we dont give a rat's ass to what they have to say. All i know is that my 250k driven car gives 13kmpl, the seals dont leak and runs like a champ.

[pwuser151563994363]

I got manipulated badly honestly, you are right 100% I’m to be blamed as well but car has run 2400km with new thick oil only and there’s no smoke, I think I’ll switch back to old oil

[Salmaanawan]

Yes just use it till it lasts and switch back to a thinner grade. InshAllah your car will give you better mileage again