mixing engine oil question=-

1998 Lumina with about 165k. Ran 10w30 for many years.
Now I have a 5 quart bottle of castrol 5w30 and I can,t get a refund.
Is it safe to use it in the Lumina and switch back to 10w30 in the future ?

The 3.1 calls for 5/30 the 3.8 calls for 10/30 so which is it?

It,s the 3.1 . The oil cap on the valve cover does say use 5w30. But I,ve been using 10w30 for along time and heard somewhere that it ain,t good to switch back and forth.

I switch back and forth every spring and fall. 5W/30 for our cold winters and 10W 30 for the hot summers, with no problems.

Most owners manuals give some kind of temperature range and oil viscosity recommendations. For example, my '97 Cadillac says 10W 30 on the oil filler cap, but the owners manual suggests 5W 30 of the ambient air temp is consistently below 60 deg F. Above this temp, 10W 30 is recommended.

You have good reason to be concerned. The Oldsmobile Cutlass 2.5 liter lifters were sensitive to the viscosity. However I wouldn’t worry at all about putting that 5/30 weight oil in the car during the winter months. Look at your owners manual, it should have some kind of chart regarding what viscosity oil to add at what ambient temps.

You have good reason to be concerned. The Oldsmobile Cutlass 2.5 liter lifters were sensitive to the viscosity. However I wouldn’t worry at all about putting that 5/30 weight oil in the car during the winter months. Look at your owners manual, it should have some kind of chart regarding what viscosity oil to add at what ambient temps.

he is supposed to use 5-30wt oil. the 10-30wt would be for temps above 40degf. if he wanted to . the spec is 5-30wt or 10-30wt. gm manual says to use 5-30wt.

don't know about that small olds block.

I know my 400cu olds used 10-30wt no problem.