When to go back to the dealer to drain excess oil.

Dear Car Talk

Dear Car Talk | Oct 01, 1996

Dear Tom and Ray:

I recently purchased a new GMC Suburban -- diesel. This is my third
Suburban, and having logged 200,000 miles on my other two, you could
correctly assume that I like these vehicles and I am very serious about
maintenance. On my last service, I noticed on inspection that the oil level
was overfilled by at least a quart. I brought this to the attention of the
dealer, who dismissed it as a bonus for me, since I hadn't apparently been
charged for it. Perturbed by his lame explanation, I decided to consult you
two gurus (guri?). What are your thoughts? -- C.W.

TOM: I think you should go back to the dealer, tell him to drain out the
extra quart, and as a bonus, tell him that you're not going to insist on
store credit for the returned oil.

RAY: Actually, yours is a borderline case, C.W. Normally, overfilling the
crankcase by a quart IS bad for the engine. If the oil level inside the
engine is too high -- if it touches the bottom of the crankshaft -- the
crankshaft can do a "Betty Crocker" on the oil, and whip it up into a nice,
bubbly foam.

TOM: That's great if you're making chiffon pie. But the problem is, the oil
pump can't pump foam. And since it can't pump foam, some parts of the
engine won't get properly lubricated.

RAY: In an engine that holds four quarts of oil, an extra quart could
definitely cause this problem. But since your Suburban holds seven quarts
of oil, it's more of a borderline case.

TOM: In general, I'd use the 20 percent rule. If your crankcase is
overfilled by 20 percent or more, it's worth draining out and correcting
right away. But since you plan on keeping this beast for 200,000 miles, I'd
play it safe and insist they take care of it, C.W.

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