Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. It only takes a minute to sign up.
Sign up to join this community
5W-30 fully synthetic engine oil exists in a Vauxhall Insignia engine but it needs topping up and I believe it should have oil in 5W-40 viscometrics.
Is it safe to top up fully synthetic 5W-30 with fully synthetic 5W-40 without causing damage to the engine?
Yes, both are fully synthetic and you should check that they meet similar specs (api etc).
When it next gets changed use the correct grade.
Yes, and if you were in an urgent situation, like a trip, you could top off with a non-synthetic if needed. The biggest issue with non-synthetic oils is normally around turbocharger temperatures oxidizing or otherwise polymerizing the oil.
If you were in an area of extreme heat, such as a desert area, it would be nicer to have the 5W-40, but for most areas, there will be little functional difference with the 5W-30. The -40 and -30 are numbers which describe the high temperature viscosity of the oil, with 40 remaining "thicker" at higher temperatures than the 30.
