A/C belt and tensioner failed. Should I also replace serpentine belt and tensioner?

Dawg82 · May 25, 2026

Serpentine belt has to come off to replace the smaller A/C compressor belt. Not a DIY guy, taking it to local repair shop. Seems like a no-brainer...Already have the A/C kit, just need to figure out whether I have a 105 or 145 Amp alternator in my 2003 LS with the 4.8L Vortec

Fless · May 25, 2026

If you don't know when the main serp belt and tensioner were last changed, it would be a good idea to replace them. Does the main belt still show any part numbers?

Look at the RPO codes inside the glovebox lid:
K68 = 105a
KG8 = 130a
KG3 = 145a

The 105a alternator doesn't have the dark-colored spacer sandwiched between the cases like the larger ones do. Sometimes the amp rating is engraved into one of the cases.

homesick · May 25, 2026

Fless said:
If you don't know when the main serp belt and tensioner were last changed, it would be a good idea to replace them. Does the main belt still show any part numbers?

Look at the RPO codes inside the glovebox lid:
K68 = 105a
KG8 = 130a
KG3 = 145a

The 105a alternator doesn't have the dark-colored spacer sandwiched between the cases like the larger ones do. Sometimes the amp rating is engraved into one of the cases.

You got me curious. I discovered I have KW1, 160 amp. Woohoo.

joe

OR VietVet · May 25, 2026

When in the belt(s), tensioner(s) and idler(s) remove mode, do it all. Hell, get a good look at the water pump and do it if there is even a hint of stain/corrosion at the weep hole and if do the pump, do the thermostat and coolant temp sensor, too. Check the fan clutch and if loose or of unknown age, maybe even original, replace it too.

Keep going, I can spend OPM all day long.

Dawg82 · May 26, 2026

OR VietVet said:
When in the belt(s), tensioner(s) and idler(s) remove mode, do it all. Hell, get a good look at the water pump and do it if there is even a hint of stain/corrosion at the weep hole and if do the pump, do the thermostat and coolant temp sensor, too. Check the fan clutch and if loose or of unknown age, maybe even original, replace it too.

Keep going, I can spend OPM all day long.

Water pump replaced two years ago

Fless · May 26, 2026

A careful inspection will tell you a lot, but I would say for now do just the belts and tensioners unless you see something else needed. Keep track of (document) what's been done and move forward.

OR VietVet · May 26, 2026

Dawg82 said:
Water pump replaced two years ago

How old is the rest of my list? When the water pump was done 2 years ago, was the thermostat and sensor done? Fan clutch condition?

Why do I ask a list of questions and only get 1 answer about 1 component?

Joseph Garcia · May 26, 2026

Dawg82 said:
Serpentine belt has to come off to replace the smaller A/C compressor belt. Not a DIY guy, taking it to local repair shop. Seems like a no-brainer...Already have the A/C kit, just need to figure out whether I have a 105 or 145 Amp alternator in my 2003 LS with the 4.8L Vortec

I change the tensioner assembly every time that I change a belt. They are not very expensive, and most belt issues are actually caused by the deterioration in the spring strength of the tensioner, due to the heat in the engine bay and constant movement when the motor is running.

homesick · May 26, 2026

Dawg82 said:
Water pump replaced two years ago

If the current water pumps are on par with the old SBC motors' pumps, I'd still give it a close look. The old style didn't necessarily fail quick, but they could sure fail sudden.

My '78 Camaro's pump had started to seep, and I did not let it linger. I bought a new one, to swap that next coming weekend. It self-destructed that Friday morning, and took the fan and the radiator out with it.

The whole car was only 3 years old.

joe

homesick · May 26, 2026

OR VietVet said:
How old is the rest of my list? When the water pump was done 2 years ago, was the thermostat and sensor done? Fan clutch condition?

Why do I ask a list of questions and only get 1 answer about 1 component?

Reading for comprehension isn't a widely practiced skill.

joe

Dawg82 · Jun 1, 2026

OR VietVet said:
How old is the rest of my list? When the water pump was done 2 years ago, was the thermostat and sensor done? Fan clutch condition?

Why do I ask a list of questions and only get 1 answer about 1 component?

Because I trust my mechanic who replaced the water pump and has done other repair / maintenance on this old beater Tahoe to let me know what I really need.

OR VietVet · Jun 1, 2026

Dawg82 said:
Because I trust my mechanic who replaced the water pump and has done other repair / maintenance on this old beater Tahoe to let me know what I really need.

See....there's the answer to my question(s).

You ask for help and I ask questions to help me help you and then don't share the info that you decided is not needed to share. All good. Really, all good. But at least tell me the history, like you finally shared. Were my questions uncomfortable? Answers to questions get to the "fixed it" result.

homesick · Jun 1, 2026

Dawg82 said:
Because I trust my mechanic who replaced the water pump and has done other repair / maintenance on this old beater Tahoe to let me know what I really need.

Then why waste your time and his genius asking our dumb asses anything?

joe

strutaeng · Jun 1, 2026

homesick said:
If the current water pumps are on par with the old SBC motors' pumps, I'd still give it a close look. The old style didn't necessarily fail quick, but they could sure fail sudden.

My '78 Camaro's pump had started to seep, and I did not let it linger. I bought a new one, to swap that next coming weekend. It self-destructed that Friday morning, and took the fan and the radiator out with it.

The whole car was only 3 years old.

joe

Oh WOW. So this was like in 1981?!

We had a 72 C20 that the exact same thing happened (it had a Buick 401(?) someone before had swapped in). It was in 1993 'cause we'd just moved from SoCa to Texas.

I don't remember what my Dad was doing or checking, but I just remember standing on the bumper looking at the engine running on our driveway and my Dad revved it up a bit and I just recall the water pump fail catastrophically and taking the fan and crashing it into the radiator. I was a kid and wise enough to jump down from the bumper, lol. And my Dad came over like, WTF just happened?!, now with steam coming out of the engine bay...

Yeah, never heard of an LS water pump do that...

homesick · Jun 1, 2026

strutaeng said:
Oh WOW. So this was like in 1981?!

We had a 72 C20 that the exact same thing happened (it had a Buick 401(?) someone before had swapped in). It was in 1993 'cause we'd just moved from SoCa to Texas.

I don't remember what my Dad was doing or checking, but I just remember standing on the bumper looking at the engine running on our driveway and my Dad revved it up a bit and I just recall the water pump fail catastrophically and taking the fan and crashing it into the radiator. I was a kid and wise enough to jump down from the bumper, lol. And my Dad came over like, WTF just happened?!, now with steam coming out of the engine bay...

Yeah, never heard of an LS water pump do that...

Yep, I was on my way to work, new pump in the trunk.

I also couldn't find a radiator before work Monday morning, so I had one built- $300 [$1200 in today's dollars].

joe

A/C belt and tensioner failed. Should I also replace serpentine belt and tensioner?

Dawg82

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