Engine Vibration -- gonna be fatal, soon?

[Mikey_K]

It's below zero up here in Wisconsin today. I got up this morning to take my kid to school for a wrestling meet, and ended up taking city streets home, instead of the freeway.

The whole car was just kind of shaking and pounding. Not steadily, kind of in bursts. I've noticed it before, at highway speeds, but it was something that popped up for a few seconds, and then went away. I had it in to the mechanic a few weeks ago, and both rear wheel bearings were replaced. I mentioned the vibration issue then, and the mechanic said one ball joint was just a little bit loose, but otherwise everything else was O.K. The front frame members supporting the lower control arms are rusty, but he thought they were solid enough.

So, I'm thinking it's just a tired mill. When I turned the heater fan up all the way this morning, I could almost see the needle on the temperature gauge fall. I don't think the engine every fully warmed up to the normal operating range. It's a 92 xFi with 159K on it. At the last oil change, I added a quart of Lucas oil supplement to conventional 10w-30 conventional oil. One full quart of Havoline 5w-30 full synthetic has been added since, to top up what's leaking/smoking away. It's by no means a smoke bomb, going down the road, although I haven't given the dipstick the 'burnt toast odor' sniff test, yet.

Gas mileage hasn't been too bad (I have a heavy foot, so I've never gotten over 45), and around town I haven't noticed anything. For the last month or so, though, at random and infrequent intervals, this shaking-pounding vibration would pop up, and it was as bad, and as consistent (even at 50, 55 mph) as it's ever been today.

Ignition parts are all pretty new, and the timing's set at the original setting. I tried bumping it up, for a while, but I didn't see a mileage improvement or other advantage, so I set it back. I failed my emissions test about 4 months ago, but that was traced to a leaking vacuum connection to the MAP sensor, and the fuel system was pretty exhaustively checked out during that troubleshooting sequence.

It's too cold to think about replacing the oil with a thicker weight, it probably wouldn't fire up at all.

Anybody have any suggestions? I'll need a little time to save up for a JDM replacement.

[Mikey_K]

Okay, I had a thought this afternoon... Maybe it's ignition related. I once pulled smoothly off the freeway and was surprised when the car coasted to a stop.

It had been running just fine. Opening the hood, cursing my luck, I was jumping up and down when I saw the coil wire had disconnected itself from the middle post of the distributor cap. I reconnected the ignition wire and haven't thought much about it, since.

Maybe there's some weird thing going on, where I'm running momentarily on two cylinders? The shaking and pounding thing seems "random", but now that I think about it, there could be a correlation with potholes and rough pavement.

I'll go back under the hood, tomorrow, and push on all the distributor cap wires. Or, is there, like, some internal thing in the coil, or a spark plug, that might not be apparent at first glance, I should know about, or can check?

[Woodie83]

Don't go any thicker, your oil is already way too thick for conditions. 10W-30 is okay if the temperature never goes below zero. 5W-30 is okay any time, any place. Adding stuff to the oil makes it thicker, you're going to burn valves.

[dwendt1978]

Check your engine mounts first. A damaged mount can show up now and then like your describing. Being in Wisconsin, (Michigan here) if I go through too thick of snow, it will pack snow in the back side of the rims and driving at 55 will about shake me out of the car. After parking in the garage at night it melts and is mysteriously gone.

[Mikey_K]

I figured it out!

It's *temperature-related*, alright.

I have two front tires that both have fix-a-flat liquid leak sealer in them. When it's below zero, that stuff stops flowing and chunks up, veryl weird and unpredictable. So what feels like engine vibration is really just the effect of a wildly out of balance right front wheel, fighting the engine.

I thought I was really lucky, last summer, when I found a couple of used Bridgestones with 90% of the meat still on them, but they just wouldn't hold air. I guess that's how come they ended up at the used tired store.

[91Caprice9c1]

Glad you got to the bottom of it. FWIW, those of you with chrome or alloy wheels should not use fix a flat for any extended period of time, as it is corrosive and will cause sealing problems at the tire bead.

-MechanicMatt