It was an engine developed by diahatsu and Toyota now own diahatsu. Its cheap and cheerful and does the job its meant to do reliably at the end of the day lol
Apparently it does,but don't ask me why lol, for whatever reason these days there seems to be specific oil ratings for specific cars/engines,unlike in the past when any 5/30 would do as long as it was fully synthetic. 🤔
By the sound of it,the soot/exhaust fumes is leaking into the car through the vents when the fan is switched on,so it is very likely that you have got some sort of leak somewhere in the engine bay🙄
I have kept mine as they are,however you shouldn't have any problems if you went down to 245.40.18 apart from your speedo reading slightly out if I am not wrong,you could probably go 235.35.18,not sure about cost though