Castrol GTX is the best high mileage motor oil, according to BestCovery.com, garnering a five out of five-point review. Conditioner additives increase the longevity of engine seals, reduce leaks and prevent sludge deposits. BestCovery also recommends Mobil 1, Pennzoil, Amsoil Extended Life Synthetic and Valvoline MaxLife high mileage oil.
Mobil 1 High Mileage oil has a 4.75 out of five-point rating. To remedy engines with existing sludge deposits, BestCovery recommends Mobil 1 High Mileage oil and shorter oil change intervals. Pennzoil High Mileage motor oil prevents sludge deposits, reduces leaks, maintains seals and eliminates oil consumption. Amsoil Extended Life synthetic oil is a long-lasting formula that allows for longer oil change intervals. Valvoline MaxLife synthetic motor oil includes additives for seal conditioning and engine lubrication, while also removing existing sludge deposits.