With oil leak, best option is ‘watchful waiting’

Dear Car Talk: I love your column. My morning doesn’t start till I’ve read it. I have a well-cared-for 2013 Ford F150, 8-cylinder, 4WD pickup. It has developed a very slow drip of oil, which I have monitored for the past three weeks.

At its regular oil change, the mechanic detected the leak without any input from me, which is great. His assessment is it’s a rear main seal failing, which seems logical based on the little I know about engines and the position of the drip.

The estimate to repair it is $1,120 because the transmission needs to be removed to replace this $20 seal. I trust this mechanic, but I have three questions: 1. Is this a reasonable price for labor for this repair? 2. Should I ask if there may be something else leaking that would cost much less to repair? 3. Can I do nothing for now and just monitor the situation daily with an occasional addition of oil, or would that endanger the engine? Thanks. — Frank

A: Yes, yes and yes.

To answer your last question first, “watchful waiting” is a perfectly acceptable strategy here, Frank. You won’t harm your engine unless you actually let it run low on oil. So, start by checking it every day. If there’s no measurable change, check it every week and keep going until you figure out your rate of oil loss. Then, just make sure it never gets more than a quarter or half a quart low.

You could have an extremely slow leak, Frank. You might not even be losing a quart of oil between your regular oil changes. Regardless, as long as you keep the oil level where it should be and the leak doesn’t suddenly get worse — which it probably won’t — you can wait to fix it.

Is there something else it could be? Sure. There’s a gasket above the rear main seal at the back of the intake manifold, that sometimes leaks on these engines. Oil dripping from there can make it look like the rear main seal is leaking, but it’s a lot cheaper and easier to fix. So, have him check that, if he hasn’t already.

He should also check the positive crankcase ventilation system if he hasn’t. If the PVC isn’t working, unreleased pressure in the engine could force oil out the rear main seal or elsewhere, even if the gasket is otherwise OK.

If it is the rear main seal, then, yes, $1,100 is about the right price because of the labor involved. So keep an eye on it and top up — until the oil stains on your driveway drive you nuts.

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