rocketman4321

Agree. Failing starters are often actually the solenoid, and that will either cause grinding (partially engaged) or no operation at all. That's why sometimes a whack on it while trying to crank "fixes" it. If "chugging" is straining or slow operation, that could be a lack of power (volts and/or amps) at the starter. Sudden intermittent brushes are possible but a bit of a coincidence.

I concur with the above list, but I'd start by charging the battery (directly on its terminals) once you're home and see if that makes a difference. (The 12.6V with the engine off seems OK, but...) Voltage doesn't change much with the state of charge, and you could be low and not read it under light load, only to have the voltage collapse when you draw heavily. Our 850 did this the week after we bought it--turned out the battery connections were dirty and it wasn't getting much of a charge. Then check the voltage while running to see if the alternator's ok. And the list above.

If the battery wasn't getting charged, take it back in and have the shop test it under warranty. A couple deep cycles can hurt a car battery, but you'd get a full replacement after 3 months.

Just to make sure on you meaning of "OEM"--genuine Volvo, not OEM-grade? I replaced mine with one of the common "OEM" ones--think they were Elring--and they didn't last long. Better to use the factory ones here, if you didn't.

Also remember to check the idler pulley as well as the tensioner. Don't just spin it--put some side load on it with your hand, like the tensioned belt does. Mine spun quietly but felt rough when loaded.

If I recall, Tasca has genuine Volvo radiators for pretty close to the same cost as the better aftermarket ones. I believe the general advice is to avoid the unnamed aftermarket ones. The swap is pretty straightforward and not all that messy if you hit the pan when you drain it....