Last winter, a 2004 Silverado 2500 with a 6.0L Vortec landed in my garage because it would not stay running. That part was embarrassing. I'm a quality/compliance manager at a metal components plant. I spend my days looking at stamped parts, dies, CNC machined parts, forgings, and all the paperwork that goes with them. But this truck still had me chasing a charging problem for two weekends.
By the time it arrived, the battery was low from repeated cranking. The owner asked, Will my car start with a bad alternator? It's a fair question. The short answer is yes, if the battery still has enough stored energy. The starter motor gets its power from the battery, not the alternator. A fully charged battery at around 12.6 volts will crank and fire the engine even when the alternator is dead.
The longer answer is more useful. An engine with electronic fuel injection, an ECM, and an electric fuel pump needs stable voltage. The alternator is what keeps voltage stable once the engine is running. When it stops charging, the battery slowly takes over until the voltage drops below what the fuel pump and coils can handle. That's exactly what this truck did: it started, ran for maybe two minutes, stumbled, and died. It was not a fuel pump failure. It was a charging failure.
I put the battery on a charger overnight, and the truck started fine the next morning. With the engine running, I measured 12.4 volts at the battery with no load and 12.1 with the headlights on. A healthy charging system should show about 14.1 volts. The alternator was bad. After replacement, the voltage came back to about 14.2 volts at idle. But that was just the beginning.
The Front Lower Control Arm: More Than the Bushing
On the first real drive after the charging fix, the front end thunked when I turned into the driveway. I hate that sound. It tells you something in the suspension is moving when it should not be moving.
On these GMT800 trucks, the front lower control arm is a stamped steel assembly with a bushing on the frame side and a ball joint on the other end. The bushing wears over time, and clunking is usually the first symptom. But I did not want to assume the bushing was the only worn part. In my line of work, a stamped part can look fine from the outside and still be out of tolerance where it matters.
When I got the truck on jackstands, the driver side rear lower control arm bushing was torn and loose. The arm itself was straight, and the bore where the bushing sits was still round. So I replaced just the bushing with a MOOG K200149 control arm bushing. That is the right choice when the control arm is still in good shape.
The passenger side was different. The metal shell of the old bushing had spun inside the arm, which ovaled the bore slightly. A new bushing would not fix that because the aluminum? Actually steel arm bore had worn into a slight egg shape. No bushing can crush into an egg shape and stay tight. That side needed the complete MOOG RK640609 control arm.
So I had two similar problems and two different fixes. One side got a MOOG K200149 control arm bushing, the other got a MOOG RK640609 control arm. In quality terms, I was deciding whether the reject was at the component level or the assembly level. If I had blindly ordered two complete control arms, I would have replaced an arm that did not need replacing. If I had blindly ordered two bushings, I would have spent a day pressing one into a damaged bore and watched it fail later.
That is the part nobody puts in a product description: the cheapest repair is the one you choose after measuring the actual failure.
The Coolant Head Gasket Problem That Hid Until Hot
Two weeks after the suspension work, another issue showed up. The 6.0L started smelling faintly sweet after shutdown and occasionally pushed a little coolant out of the overflow bottle. There was no puddle under the radiator, no wet carpet, no obvious hose leak.
This is where the phrase coolant head gasket gets confusing. People type that when they see coolant disappearing without a visible leak. Sometimes it really is the water pump, radiator, heater core, or a small hose. But sometimes it is a head gasket that only opens when the engine is hot.
On my truck, the cooling system held cold pressure fine. I tested it at about 14 psi for 20 minutes and saw almost no drop. But after a 15-minute drive, the reservoir started bubbling and the pressure climbed. That is a classic hot-only coolant head gasket failure. The gasket seals when cold, then opens a tiny path between a cylinder and a coolant passage once the engine expands.
I pulled the passenger side head and found a dark stain running from a water jacket into the cylinder. The piston top in that cylinder looked steam-cleaned. That is what coolant wash does. It cleans the carbon off the piston and leaves a surface that looks almost new.
The fix involved more than a new head gasket. Coolant in a cylinder can disturb the oil film on the cylinder wall, and that makes the rings work under bad conditions. This engine had also used about a quart of oil every 800 miles, which pointed to tired rings. Once I measured the cylinder bores and found them within specification, I decided to replace the rings while the head was off.
That is where 6.0 LS piston rings come into the story. The 6.0L LS engines are tough, but they do wear ring packs and develop oil consumption. New rings are not a substitute for measuring the bore. If the bore is scored or out of round, rings will not fix it. In this case, the bores were still good, so I did a light hone and checked every ring gap before assembly.
Ring gap is one of those details that looks small until it costs you an engine. Too tight, and the ring ends meet under heat, which can scuff the cylinder. Too loose, and oil gets past the rings into the combustion chamber. On a 6.0 LS, the piston ring gap specs are published for a reason. I checked each one with a feeler gauge, wrote the numbers down, and kept the ones that fell within spec.
I don't have hard data on how many 6.0L trucks get rebuilt with new piston rings without anyone checking the bores first. I just know that at my plant, we reject parts based on measurements, not guesses. An engine is the same way. Parts that look right at a glance can still fail under load.
What I Learned From This Project
That Silverado ended up costing more than the owner expected. They always do. But the real lesson was not about parts prices. It was about diagnosis.
Will my car start with a bad alternator? Yes, it can, as long as the battery has enough reserve. It may not stay running, and it may not restart after you shut it off. The starter does not need the alternator, but the engine management system does.
For the control arm clunk, the lesson was to inspect the arm bore before choosing between a MOOG K200149 control arm bushing and a MOOG RK640609 control arm. The bushing is the smart fix when the arm itself is still true. The complete control arm is the honest fix when the housing is damaged.
For the engine, the lesson was patience. Coolant loss with no puddle is not always a head gasket. But a real coolant head gasket leak can hide from a cold pressure test. Test it hot. And if the engine is a 6.0 LS with oil consumption and the bores are still good, replacing the 6.0 LS piston rings is a solid move when done with the right prep.
At the end of the day, the most expensive part is the one you install twice because you skipped a measurement the first time. Trust me on that one.