Regular oil changes keep an engine sludge-free

Dear Car Talk:

Am I negligent? I assume so, since I have not had the oil changed in my 2011 Hyundai Tucson since 2015. I put lots of short trips on this car, and it doesn't even have 40,000 miles on it yet. Yikes, I fear. What say you? – Steve

RAY: Don't worry, Steve. I'm not going to yell at you or publicly embarrass you. You were right to come forward and 'fess up so we can help you.

Steve, you idiot! Sorry, that slipped out.

As you’ve correctly surmised, what you did is not great. The reason we change our oil every 5,000 or 7,500 miles (or 10,000 or more if it’s synthetic oil) is to keep the engine properly lubricated.

With the metal parts inside your engine rubbing against each other thousands of times per minute, good lubrication is the difference between your engine having a long life and a short life marred by lots of burning oil.

And oil provides more than just lubrication, as crucial as that is. Oil also picks up contaminants and dirt inside the engine and holds them in suspension.

If the oil gets saturated with dirt, and can’t absorb any more, that dirt’s going to stay in your engine. And in the worst cases, we’ve seen more than an inch of sludge in the valve train. Those engines are toast.

You may be lucky, Steve. Maybe the automotive gods were smiling on you, and, despite not changing the oil for the past 20,000 miles or so, there’s no sludge in your engine.

That’d be great. Then all you have to worry about is that poor lubrication will lead to oil burning down the road. And you can solve that problem by selling the car to your brother next week. That’s what I always did.

But if it were me, I’d want to know. I’d ask my mechanic to take off the valve cover and peek in there.

If there’s an inch of sludge in there, you’re either looking at an engine rebuild, or a new vehicle as soon as voluminous plumes of blue smoke start billowing out your tailpipe – which won’t be long from now.

If the valve train looks reasonably clean, then you should thank your lucky stars, change the oil and set a recurring event in your calendar to change the oil every six months. Then set about 15 or 20 reminders so you can’t ignore it.

Could transmission trouble in rebuilt engine be a faulty sensor?

Dear Car Talk:

I have a 1997 Dodge Dakota V8 with an automatic transmission that was rebuilt about 5,000 miles ago. Now when I drive it, it shifts fine for the first couple of miles, but once it warms up, it doesn't want to shift into Third unless I put it in Neutral for a couple of seconds and then back into Drive. I've verified the fluid level is correct and the adjustment on the throttle cable seems right. What else could cause this? – Rusty

RAY: I'm guessing you got a 4,500-mile warranty on this rebuild, right, Rusty?

I would definitely go back to the rebuilder first and ask for some help. It’s certainly possible that something went wrong with the rebuild. Or a part failed that got reused instead of replaced. Even if you’re outside the meager warranty period, I think you’re within your rights to go back and say “Hey, fellas, what gives?”

I can give you a few ideas, but it’s not like there was one thing that always went wrong with this particular transmission. Lots of things went wrong with this transmission.

One area of inquiry is mostly electronic. This transmission is partially controlled by a computer called the Powertrain Control Module (PCM).

But in order to know when to tell the transmission to shift gears, the PCM has to collect data from a bunch of sensors. Any of those sensors could be faulty. And if the PCM is getting bad info, it might not call for shifts correctly.

For instance, there’s a transmission speed sensor on the transmission’s output shaft. There’s a vehicle speed sensor. There’s a transmission pressure feedback sensor, and a transmission temperature sensor.

And don’t forget about the “time to buy to buy a new truck, Rusty” sensor.

If it’s not something electronic, you have to consider the mechanical or electro-mechanical stuff inside the transmission. That’s the stuff you hope they had rebuilt or replaced.

There you have various solenoids, pressure activated valves, the governor pressure sensor and don’t forget the lieutenant governor pressure sensor.

That’s why my first suggestion was to go back to the guy who did the rebuild for you 5,000 miles ago, and hope he’s got a kind heart and a good diagnostic mind. And bring fresh brownies. Good luck, Rusty.

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