On my "04" Buick LeSaber with 84,500 miles.

Do we wait for the car to tell us when to get new spark plugs ? Or is there a test to find out?

Or do it at a certain mile mark?

The service/replacement interval in the GM Preventative Maintenance Schedule for the 2004 Buick LeSabre is 100K miles

My '02 Olds Alero calls for sparkplug change at 100,000 miles.

I'm not quite half way there, but I may replace them some day, hopefully before they rust in place.

No. Probably not.

...therefore plan to change the spark plugs on the Buick on Sunday, January 27, 2030...

Something to consider. Generally speaking the plugs are not that expensive. Your Buick is about 21 years old and those plugs have likely been installed for 21 years. Those plugs are probably going to be pretty hard to remove at this point. If you wait another 15-20 thousand miles and another five or so years they will likely be a real pain to replace.
If you change them yourself put a little bit of anti-seize on the threads. Whoever tries to remove them next time will thank you.

They are generally replaced by mileage intervals. You can wait until they completely wear out and the engine starts missing, but this is not usually recommended. Figure on a set of spark plug wires as well, as they often get jerked out by the roots trying to remove them after 20 years stuck on. And use the same brand and type as OEM. For this car, that means AC Delco, probably iridium.

Be careful about the time/mileage interval on spark plug changes if you have aluminum cylinder heads.
On my Jeep Commander with the 5.7 Hemi engine the factory says to use the old type of spark plugs and to change about every 35000 miles.
I wondered why I could not use the higher priced plugs and found out that because of the steel threads and the aluminum heads threads and the long threaded area, Chrysler wanted the plugs removed more often so there was less of a chance of the different types of metal fusing to each other. With 16 spark plugs you certainly don't want some of them fused in place.
I always use a high temp grease on the threads.

You should probably go ahead and change them out. I would guess Buick wants them changed after about 40,000 miles. Even though you're getting good gas mileage indicating efficient operation, you know the plugs are very old.

You can take the plugs out and examine them with your eyes. Maybe clean them up a bit, check them with a feeler gauge.

quote:

Originally posted by bdylan:
You should probably go ahead and change them out. I would guess Buick wants them changed after about 40,000 miles. Even though you're getting good gas mileage indicating efficient operation, you know the plugs are very old.

Buick says change them at 100K miles!

quote:

Originally posted by nhracecraft:

quote:

Originally posted by bdylan:
You should probably go ahead and change them out. I would guess Buick wants them changed after about 40,000 miles. Even though you're getting good gas mileage indicating efficient operation, you know the plugs are very old.

Buick says change them at 100K miles!

In that case, the plugs appear to be good on the mileage interval.

Are some of them hard to get to? I'd pull an easily-accessible one and take a close look at it. Any carbon build-up and/or electrode erosion, I'd replace them all. Yes to the anti-seize and new plug wires upon replacement. There are two types of anti-seize formulations, Al and Cu, I think that the Cu is preferred for this application. If the plug is dirty, it wouldn't hurt to pull the distributor cap and take a look at it too.

NGK plugs are generally accepted to be superior to AC/Delco, Motorcraft and other OEM brands. IME, Bosch are not up to their reputation, but I would use any of them if necessary.

Given they are 21 years old and you have 84k miles, I would suggest changing them!!!!

My 2000 Grand Prix 3.8L went just under 300K on only two plug changes.
Neve had any issues and Gas milage never changed.

At this point I think you are already into the if there are going to be issues getting them out from age or corrossion or whatever its not going to get worse. So if you don't have any misfires or other driveablity issues I'd just go to the 100K.

My old Silverado had 100,000 mile plugs and that is when I changed them. I used to keep a mpg log for the truck, and in hindsight:

the mpg went down after 90,000 miles

after changing spark plugs, mpg went back to pre-90,000 mile levels

Do you have the 3800 in there? The rear plugs were a pain to change when I had the 3800 in my Pontiac.

A good set of plug wires and new AC Delco plugs would keep that 3800 purring for a long time.

Three years ago I bought a 2003 Buick Century from a family member. It had 49k on the odometer.
Because it had sat so long, I replaced the radiator hoses and had new spark plugs and wires/coil packs put on it.
It also needed tires that very next summer.
Call me over cautious, but now I know the condition of those components. Cheap insurance, if you ask me.

Nearly everything I have had to do to the car has been from sitting. Tires, struts, recharge the AC, a few plastic/rubber components, a vacuum line here and there. And I did have to put a new PCU on it recently.
Still, it has been really cheap transportation.

quote:

Originally posted by Some Shot:
My '02 Olds Alero calls for sparkplug change at 100,000 miles.

Have you had to replace the fan control resistor yet? You need to be upside down in the passenger seat. I leave one screw out. I was having to replace it once a year. I never replaced the plugs in my '01 Alero. I got rid of it at 104k because of the constant wheel bearing issue.

I used to do spark plugs every 20k on my bmw that i had tuned. nowadays, I just do plugs at 75k.