Help just put the wrong type of motor oil in my wife's car

[Rod-Knox]

Oil stabilizers increase the viscosity of oil. In other words, a blend of Lucas and 5-30 will be something heavier, 8-35, or 7-42 for instance. The much lighter weights(near the consistency of water) are recommended to match the close tolerances of todays engines. At temperatures below freezing the light oils becomes somewhat more critical as temperatures fall to zero and below engine damage can result. Locally I have seen weather near zero prevent cars from starting with 10-40 in the crankcase and rebuilt one engine that was trashed when driven with 20-50 oil and stabilizer in such weather.