What is the OEM recommended viscosity for a 1992 Toyota Paseo? I had it in south TX now I use it in Fairbanks, AK. It has a 1.5L with 197,000MI and does not use oil as long as I keep the revs below 4000 rpm. In TX I was using MC 15-40 or MC 10-40 (cheap) at 100F+ temps. Now I use 2qts of Shell Formula 5-20 and 1qt of Valvoline SynPower 20-50? Both were on sale for .99/qt I just had to buy a case of each. With a 2.9 qt capacity I dump the oil every 4500MI. Will this custom witch doc blend hurt my toy's mill? BTW it does have a block heater and oil pan heater for those -40F days. Thanks.