Drive it forever: One-quart overfill probably OK

Dear Mike: I took my 2007 Scion TC to the dealer for its first oil change. The specs call for four quarts of oil, but the tech put in five quarts instead. I drove it 270 miles before I noticed the error, and then I went back and had them restore it to the proper level.

Is there any chance that this mistake caused damage?

A: Overfilling a crankcase can potentially lead to leaks from damaged seals and gaskets. The problem is that the inside of the oil sump gets pressurized when excess oil gets whipped into a froth by the crankshaft. The crank normally spins merrily away several inches above the oil level in the sump. This can overpower the crankcase-ventilation system, pop gaskets out of place and make the crankshaft and camshaft rotating seals invert.

But a one-quart overfill probably wouldn’t do it. If you haven’t seen any problems, and if the oil level has been lowered to normal, then relax.

Dear Mike: Some 10W-30 oil was accidentally “added” into my car’s bell housing through a rubber plug that was mistaken for the transmission oil-fill port. Yes, 10W-30 motor oil is the correct transmission lube, according to the manufacturer.

I realize that the best way to remedy this sorry situation is to replace the clutch, clean out the bell housing etc. I estimate that’s about $400 of professional labor, or about eight-and-half hours of my time.

As an alternative, I was thinking that I could flush out the oil by choosing the right solvent sequence, ending with a fairly volatile solvent that could be allowed to dry slowly.

My questions: If I go ahead and flush, say, two quarts of kerosene, two quarts of gasoline, then two quarts of pentane, won’t these solvents work into some nearby rubber seals? How might I expect the seals to respond?

A: Anything more aggressive or volatile than kerosene may well degrade the engine’s main crankshaft seal and the transmission input-shaft seal. Such a solvent also might compromise the integrity of the paper-based clutch facing. That will fail spectacularly, and leave you with either a clutch that won’t grab or one that won’t release. In addition, any solvent, including kerosene, could carry grit into the throwout bearing.

But, really, what have you got to lose? I say, try some kerosene. If you get enough oil out of the works to let the car be driven — carefully — without slipping the clutch, heat and centrifugal force will purge the oil within a few hundred miles.

But before you start: If you have tried to drive the thing and glazed the clutch by slipping it, it is already too late. You will have to bite the bullet and tear it down.

Dear Mike: I currently drive a 1992 Chevy pickup that has 243,000 miles on the odometer and still runs well. I bought it used, and I am not sure if the motor has been overhauled. I have had the transmission rebuilt, but the motor seems to be running strong.

It just stalls when it is really cold, after I first start it and try to drive it. Do you have any suggestions to fix the stalling problem?

A: I would check the fuel pressure to be sure that it is high enough. Then I would add some fuel-injection cleaner, and clean the throttle body and idle air controller. Check the throttle-position sensor too.

Dear Mike: I noted that your long-term test of the Honda Fit Sport in the June issue of Popular Mechanics said that your testers “overheated the brakes and failed to cool them down properly.” Please advise the “proper” way to cool overheated brakes. I’m not familiar with the process, and would sure like to know how I might save a set of rotors.

A: Damage occurs when the pads cook on the same spot on the rotor while they cool off from their incandescent phase. Cooling off overheated brakes is simple: Drive around at modest speeds, slow enough not to need the brakes, for about five minutes. This will keep the pads from sticking to the hot discs, and keep the discs from warping from the concentrated heat in the area covered by the pads.