seen a petrol powered pressure washer with a 4 stroke 200cc engine rated at 6.5hp. it states to use sae 30 oil. from what iv been reading up on here the 30 rating is when the oil is hot, so why not use a fully synthetic car engine oil that is multigrade like 5w30 or 0w30? since when up to temperature it would be a 30 grade like sae30 but when cold / startup it would flow a lot better than the straight sae30 grade? or are these types of engines very particular on using the conventional sae30 thats specced in the manual?