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Disguised diagnostics: When one automotive issue cloaks another

Wednesday, March 1, 2017 - 08:00
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Those of us who have attended manufacturer schools know full well how important the progression of a repair goes. First, the concern must be verified (if possible). The freeze frame data helps in that regard with drivability problems, because that snapshot provides what Chrysler used to call a “similar conditions window.” But then there are those problems a scan tool can’t detect, but our ears and eyeballs can. Spraying or dripping fluid leaks. Engine noises from inside and outside; whining alternators and power steering pumps; rattling or rumbling A/C compressors. Those are easy to verify, but some of them can be difficult to pinpoint.

Back in 1977 I was working at a small independent shop for a guy named Ed Davis. That shop had a concrete floor, but no lifts, and it looked like a big barn, but it was in a good location. One day a ’70 model Ford pickup came driving in the door, and it sounded for all the world like something major in the engine was about to come undone. I stood there thinking we had a major overhaul on our hands, but Ed had the owner switch the engine off, and then he took his pocketknife and cut both belts off. I noticed that one of the belts was gapped and had chunks missing, but so what? That noise was nasty – surely there was metal on metal hammering somewhere! But when the owner restarted the truck without the belts, it sounded so smooth and quiet that I absolutely couldn’t believe my ears. A new set of belts fixed that one. Since then, I’ve been smacked around a few times by one problem either imitating another or cloaking one. 

This is a nice truck — well worth the cost of an engine.

The Titan

The subject of today’s article — a 2005 Nissan Titan with 157,647 miles — hadn’t been driven for a while because the owner was certain that the engine was destroyed, and she wanted us to listen to it. She said her husband had driven it until the oil light came on and kept driving. That sounded serious, but we figured we’d evaluate it anyway. She left the truck one night after we were closed and gone and we looked at it the next morning. We initially noticed two things. First, before we even started the engine, we found that the oil wasn’t touching the stick, but it only took three quarts to put it on full, so it wasn’t low enough for engine damage, and she didn’t mention having added any oil.   

When we started the engine, it was rattling to beat the band in the bell housing area and leaking oil from the rear main so fast that it made a puddle nearly two feet in diameter within three minutes. Seldom do we see a pressure-driven leak that bad this side of a double-gasketed oil filter.

I have seen a lot of cracked flywheels, but this one took the cake for having been driven many a mile until it began radiating cracks from the bolt circle.

The noise sounded suspiciously like a cracked flywheel, but we didn’t hear anything else – that being said, how long do you want to let an engine run when it’s bleeding to death, and who could hear anything over that nasty rattling in the bell housing anyway? It was telegraphing all over the place. I called and suggested that she let us jerk the transmission out for some exploratory surgery, and she agreed. What we found was a very seriously cracked flywheel. Not only was it cracked around the bolt circle, it had cracks radiating toward the ring gear. This was a big noisemaker. A new flywheel from Nissan is only a little more than a hundred bucks, and we got her to agree to the flywheel and a rear main seal. We had also drained the transmission oil (which was kind of black), and she’d get the new red stuff too. This transmission has a metal screen that can be cleaned and reinstalled. Justin steam-cleaned the muddy transmission and the other parts in preparation for the reassembly, but the flywheel wouldn’t be in for a couple of days.

Altima engine swap   

About that time, we drew an engine swap job on a 2005 Altima that came in rattling like a diamondback, and the owner was savvy enough to have a replacement engine dropped off right after the car rolled in. Externally, the replacement mill was rusty on the steel and chalky on the aluminum - it looked like it had been sitting somewhere damp, but it turned easily with the breaker bar and there was no sludge we could see in the oil splash area through the filler cap hole, so we didn’t even yank the valve cover. It did get a rear main seal just for grins. I considered transferring the catalyst heat shield from the original engine, but those little bolts will usually snap when you try to remove them, so I left it be.

With these two grounds swinging, the Nissan would just sit there and spin, which isn’t particularly surprising. What’s worse is when the guilty ground is buried somewhere out of sight.
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