Dear Car Talk:
I recently learned that my mechanic has been filling my 2008 Chevy Impala with 5 quarts of oil, instead of the recommended 4.
I've also noticed an oil leak, which my mechanic attributes to a bad manifold gasket or head gasket.
Could overfilling the oil have caused these gaskets to leak? It's a 3.9 liter six-cylinder engine with 104,000 miles on it. -- Michael
No. It sure would be nice to blame this guy, wouldn't it, Michael? But overfilling the crankcase by 1 quart is not likely to cause any problem whatsoever.
Not that we make a habit of it at the garage, but that happens sometimes. The mechanic should have checked both the oil capacity and the dipstick. But he may have assumed that a large, six-cylinder engine like yours would hold more than 4 quarts. Most of them do.
But your oil leak was caused by those 104,000 miles you put on the car. And it could be a big job to fix. If you need to do both cylinder heads, you could be looking at well over $1,000. Even if it's just the manifold gasket, it could cost several hundred bucks, which is still not cheap.
So, unless it's leaking a lot of oil, you may want to apply the technique of "watchful waiting." That's the program my wife has me on. It involves three steps: 1. Keeping a close eye on the oil level. 2. Topping it up whenever it's low, and 3. Putting a piece of cardboard on your garage floor before it looks like the Exxon Valdez has been dry-docked in there.
If you're losing less than a quart every 800-1,000 miles, you can even bypass the cardboard box, because you'll be losing a drop every few miles on the interstate. And if that's the case, this leak is of little consequence. It's possible that something much worse will befall this car before the leak ever has a chance to become a mechanical threat.