Please advise on what viscosity oil would be best for use in 1978 Corniche, mileage 98,000. The climate in this part of country has 4 seasons, winters can have lowest temperature of 32 degrees F at night and 102 is the hottest in summer
If your engine has been completely clean inside, specially the old mude from 40 years oil.....and if it is in excellent condition, then choose a full synthetic 10W40.
If the engine might be dirty inside, no full ynthetic, but half synthetic 10W40