mrgto

for my '03 Ecotec Cavalier. Why would it be bad for me to run either 15W40 or 15W50 or even 20W50 synthetic or non synthetic in my new car? I know the manual calls for 5W30 in cold weather and is fine with 10W30 in warmer climates.
What kind of damage could be done to the motor if I use the HEAVY weight oils?

Thanks.

mrgto

TTT

Patman

I definitely would not run such thick oils in there. Most new engines nowadays have tighter clearances, so 50wt oils will just rob you of power and slow down the oil flow, resulting in higher oil temps too. Running a thick oil in an engine that doesn't need it will just result in higher engine wear. In oil analysis, if you run a thicker oil than you need, you'd see higher levels of lead, indicating higher bearing wear.

Stick with 5w30 for this engine and you'll be just fine.