Retired mechanic needs a refresher

Dear Car Talk:

For two years, my husband (a retired mechanic) had been driving my old 2003 Blazer two days a week. It has 135,000-ish miles on it. It has a coolant leak, so he only drove it around town – no more than a 20-mile round trip. He says he smells antifreeze when he drives it, but he doesn’t see any puddles or leaks, and he doesn’t think it’s the heater core.

Cut to a month ago. My son (almost 40, so not a dumb kid) was visiting from out of state and drove the car about 5 miles to a friend’s house. Hubby warned him to keep an eye on the gauges and explained the situation.

Needless to say, a loud banging started in the engine while my son was driving. He immediately pulled over and called home. Hubby told him to cautiously drive home so he could look at it. Hubby then announced that it’s my kid’s fault that the engine threw a rod.

Then a week ago, Hubby tries to start the truck and … no banging, no puddles, oil level is good. Your best guess as to a diagnosis? Thank you. – Angie

RAY: My diagnosis is that Hubby's mechanical skills need refreshing. In retirement, they've clearly fallen behind his Mahjong skills.

If the truck started up and ran quietly last week, it never threw a rod. More likely, it severely overheated. If Hubby didn’t keep the coolant topped up, or if the leak got suddenly worse while your son was driving (perhaps at 85 miles an hour), there may have been so little coolant in there that the engine overheated violently. And the steam that’s created when the coolant boils is what makes that hammering sound. It’s like the knocking sound that steam radiators make when there’s air in your home heating system.

The question now is: How much damage was done to the engine when it overheated? To find out, the first thing to do is to top up the cooling system. It’s probably empty or near empty. Once the cooling system is full, run the engine until it gets up to operating temperature. Then do an oil pressure test. Hubby probably still has an oil pressure gauge somewhere.

Often, when an engine overheats severely, it damages the engine bearings. And an engine with damaged bearings won’t be able to hold oil pressure. That’s the kiss of death. Or, as they call it in the junkyard business, “new inventory.”

So if the engine flunks its oil pressure test, then throw a jug of coolant onto the passenger seat, and hope the Blazer can make it to the nearest junkyard. If the oil pressure is OK, then you dodged a bullet, and you can probably salvage this heap, Angie.

And the next step would be to figure out where the coolant is leaking and fix it. It could be the water pump, a hose or even the heater core, despite Hubby’s earlier dismissal. But whatever it is, he should fix it now. There’s a good reason you’re not supposed to drive around with a serious coolant leak. And you guys have just had a front row seat to it.

If it’s something expensive, like a head gasket, a cracked head or a cracked block, Hubby might decide it’s not worth fixing. And we’d probably agree with him. But if it’s something relatively simple, he should fix it instead of risking the engine and jeopardizing the family peace at Christmas dinner.

What makes a Ford Explorer roar?

Dear Car Talk: I have a 2008 Ford Explorer Sport Trac, which runs great. But after driving approximately 15 miles or so, it starts making a roaring sound. Sometimes the open-ended wrench symbol on the dashboard comes on. But as soon as I stop and restart the car, the symbol goes away.

I had the transmission rebuilt a little over two years ago for $3,500 at AutoNation where I bought the car. Any ideas? – Willie

RAY: Yeah. I'd go back and reintroduce yourself to your friends at AutoNation. The open-ended wrench symbol is Ford's "drivetrain malfunction indicator." The drivetrain is pretty much the engine and transmission. So that doesn't narrow it down very much. But by scanning your car's computer, a mechanic can narrow it down a lot more.

Whenever the drivetrain malfunction light comes on, the car’s computer will store a code that tells your mechanic why the light was triggered. From your description, my first guess is that your transmission is not upshifting for some reason. That could explain the “roar” you’re hearing.

Let’s say your truck normally shifts from second to third gear around 25 miles an hour. If it got stuck in second gear, by the time you reached 35 or 40 mph, the engine could be running at over 4,000 rpm. That would make it sound more like an Airbus A320 than a Ford Sport Trac.

If you’re lucky, Willie, and you’ve led a good, clean life, it might be something simple like a sensor or a solenoid in the transmission. And if it consistently corrects itself when you restart the car, that does suggest something electronic rather than something mechanical. That would be good.

It could also be a sticky valve in the transmission, which would not be the end of the world – or the end of the Sport Trac. And if you’re really lucky, those guys at AutoNation who charged you $3,500 to rebuild your transmission will feel a bit guilty, take pity on you and fix it for you for nothing.

I wouldn’t count on that. But it’s worth going back and asking them what set the light off, and if it could be related to the work they did two years ago.

About the Author