Tractor Supply still has M1 for 2.99 qt. but in my area they only have 10W-30, I bought a case thinking I'd use it in my lawn mower I have a 2005 Dodge Caravan with 119,000 miles and I use M1 5W-20 so I was thinking maybe mix 1 qt. of the 10W-30 with 4 qt. 5W-20 for the van, how much change would the 10W-30 have on the 5W-20 ? Good-Bad ? or let the lawn mower enjoy the finer things in life ?