The Esoteric Decision of When to Change Spark Plugs

[GoGoGirl]

(Note: My M1009 does have a 350 SBC, not the stock 6.2 diesel)

I thought that title would get your attention and spark (no pun intended!) some discussion.

I use OEM AC Delco plugs. That's what was in there when I got the truck, and that's what I put into it when I bought it. I see no need to pay extra for what would probably be miniscule improvements from other plug designs/metals...unless someone can convince me otherwise.

What I do want to discuss is the topic of when to change. Looking around the net or reading manuals, everyone talks about mileage or time being metrics of change. My concern is neither; my K5 plugs have about 200 miles on them, and a year and a half of time.

An old school mechanic I know is helping me prepare (hopefully) to daily drive my truck this summer. He knows about the misadventures I've had with this vehicle, such as one very bad engine flooding incident and a couple not-as-bad ones. He says that I should change the plugs even though it now fires up fairly easily and seems to run well.

Of course I thanked him for his advice, then went online and looked around. Nobody seems to address this question, rather I see the same discussions over and over about changing plugs based on time or mileage. Personally I say that the darn thing seems fine and I'd rather leave it alone until time or mileage become factors.

What do you all think?

 

[Bent77]

I run em till they:

a) look bad
b) work bad or miss
C) changing plug wires/cap/rotor, then everything goes

Caveat also being is the engine is using oil or is not tuned right, that comes back to a and b

 

[K5wrench]

(Note: My M1009 does have a 350 SBC, not the stock 6.2 diesel)

I thought that title would get your attention and spark (no pun intended!) some discussion.

I use OEM AC Delco plugs. That's what was in there when I got the truck, and that's what I put into it when I bought it. I see no need to pay extra for what would probably be miniscule improvements from other plug designs/metals...unless someone can convince me otherwise.

What I do want to discuss is the topic of when to change. Looking around the net or reading manuals, everyone talks about mileage or time being metrics of change. My concern is neither; my K5 plugs have about 200 miles on them, and a year and a half of time.

An old school mechanic I know is helping me prepare (hopefully) to daily drive my truck this summer. He knows about the misadventures I've had with this vehicle, such as one very bad engine flooding incident and a couple not-as-bad ones. He says that I should change the plugs even though it now fires up fairly easily and seems to run well.

Of course I thanked him for his advice, then went online and looked around. Nobody seems to address this question, rather I see the same discussions over and over about changing plugs based on time or mileage. Personally I say that the darn thing seems fine and I'd rather leave it alone until time or mileage become factors.

What do you all think?

In my 76 K5 with the 400 small block that burns a quart every 500 miles, I replace plugs about every 10,000 miles.
Because I have 2 Blazers now, I don't drive either one as many miles; they share.
Drove that 76 2,400 miles round trip to see my Dad once.
Got 9 mpg with that 400.
Cracked the porcelin insulator on one of the plugs.
Never had that happen before.
Random misfire in Evanston Wyoming made me pull over.
Replaced them all on the side of the road and kept going.
Still got 9 mpg with the new plugs.
Them 400 small blocks can pass anything on the road except a gas station.

Something i noticed back before i jetted my quadrajet for altitude; it would flood real easy.
I live at 9,000 ft and the nearest town is at 4,000 ft.
My original jetting was from sea level.
Plugs would be dark.
I dropped 2 sizes on the main jets and left the seconday alone.
Plugs come out light tan now and flooding is gone.
Another issue quadrajets have is leakage out the lead plugs into the primary bores.
Makes em flood when they are starting warm and hard cranking when they been sitting.

Anyhow, no matter what you have; Quaddrajet, Holley, EFI, if you have issues like flooding, them plugs can tell you a lot about how it's been running over the long haul.
Might not be a bad idea to pull them and check em once in a while even if you don't replace them.

 

[Vombrown]

(Note: My M1009 does have a 350 SBC, not the stock 6.2 diesel)

I thought that title would get your attention and spark (no pun intended!) some discussion.

I use OEM AC Delco plugs. That's what was in there when I got the truck, and that's what I put into it when I bought it. I see no need to pay extra for what would probably be miniscule improvements from other plug designs/metals...unless someone can convince me otherwise.

What I do want to discuss is the topic of when to change. Looking around the net or reading manuals, everyone talks about mileage or time being metrics of change. My concern is neither; my K5 plugs have about 200 miles on them, and a year and a half of time.

An old school mechanic I know is helping me prepare (hopefully) to daily drive my truck this summer. He knows about the misadventures I've had with this vehicle, such as one very bad engine flooding incident and a couple not-as-bad ones. He says that I should change the plugs even though it now fires up fairly easily and seems to run well.

Of course I thanked him for his advice, then went online and looked around. Nobody seems to address this question, rather I see the same discussions over and over about changing plugs based on time or mileage. Personally I say that the darn thing seems fine and I'd rather leave it alone until time or mileage become factors.

What do you all think?

Here's some advice for you: Dance with the one that brought you. The standard in today's society is to get online and ask a bunch of random people who have equal bearing online and VASTLY different knowledge bases. If you have a good, even "oil school" mechanic that knows what he's doing helping you do things then you need to do what he tells you to do.

Now then, he is telling you to change your plugs after a bout with flooding even though the truck is now running fine. Do it....and here's why. When you run an engine really rich for a while it builds up a layer of crap on most everything inside the combustion chamber. Your pistons and cylinder will eventually cook it or wear it off but not really on the plugs. Pull them and check them. You'll see why you need to change them.

 

[diesel4me]

I like AC plugs best,but haven't had to replace one in 15 years since I parked my van--and got the 82 K2500 with the 6.2..
There are days I wish the 6.2 had spark plugs too though--the ones below 10 degrees when its a 60/40 chance it wont start..and I've probably replaced 2 dozen glow plugs since I got the truck in late 2003..

I used to change spark plugs only when they needed to be--I had to replace many due to rusting so badly I was afraid the hex portion wouldn't let a socket grasp it well enough to unscrew them--they got that way after 3 winters of salt exposure..
It never hurts to pull the plugs and inspect them ,as noted above,they give a good indication of the fuel mixture "tune" and engine condition..

After I started working in auto parts stores,I was able to get good discounts on parts for my own vehicles,so I would do a complete tune up every 10,000 miles ,or sooner if something acted up..

Some vehicles can go 100,000 miles on the same spark plugs,so says some manufacturers ,but they aren't who is going to snap them off in the cylinder head trying to remove them either...on a Chevy small block you can go more than 10,000 miles easy ,if it uses no oil and you do not flood them..but they are fairly cheap,and it'll help keep the mpg and engine condition better if they get replaced after that many miles..

Some GM vehicles used to flood spark plugs bad back in the 70's,due to failed choke pull offs,especially on a cold day,on the first start attempt..it would snuff out all 8 plugs,once the engine started and ran,then loaded up and finally stalled,usually you couldn't get one fart on further attempts to crank it up..it would just crank over till you killed the battery..

You had to install 8 new or good used plugs,and the engine would start right up again--but also flood again, if you didn't hold the choke open ,or fix the pull off..

Champion plugs did this the most,but AC's did it too--usually an AC plug would let the engine start again after it sat awhile and all the excess gas evaporated..after the engine warmed up some the plugs cleaned themselves and it would run good again..

Champions never fired again,usually,and had to be discarded..the worst years they did this was around 1975-77,when GM had the bright idea of using extended gap spark plug gaps as wide as .080..a few years later,they went back to .035 to .045 on most of their engines..

 

[dyeager535]

I run my plugs until I feel like pulling them, and if I do, and the gap is over about .045, I re-gap them and throw them back in.

I'm pretty certain some of the plugs in the truck now (AC Delco's of course) are 10 years old. Broke one or two when swapping headers, but the others looked fine, so I continued to run them. Fuel injection I'm sure helps because it just doesn't carbon up things like before, but they also don't have a ton of miles on them, maybe 30K.

If nothing else changes, and it starts to run differently, I'd probably at least take a look at the plugs.

Back a few years, it would be nothing for me to pull the plugs, if they were "sooty" but not eroded a large amount, I'd scuff the electrodes (the two on standard plugs, side and center/ground), set the gap, and throw them back in. I almost always have watched my fuel economy, for things like this it's a pretty good indicator if the plugs are working, and I never had a bout where economy or engine performance suffered.

 

[GoGoGirl]

Been busy as a bee, but reading all replies, thanks everyone.

I always carry a spare set of plugs so I may as well change them when time allows.

When I took out the plugs that were in there from the previous owner, somewhat to my surprise they looked perfectly normal. I compared them to a few online "read this plug" photo galleries just to be sure. The coloring and electrode wear revealed nothing concerning.

For an engine with an unknown history, I'm generally liking this one. Zero oil consumption, which baffles me, but for which I'm thankful. Will have to see what the current plugs reveal when I pull them.

 

[dyeager535]

Another topic is don't go crazy with spark plugs. Generally people have great luck with the AC Delco's. And generally the other stuff (I'm looking at you E3) is gimmick.

I have seen later model vehicles really tear up plugs by 50K miles, and from what I can tell it's because they are running relatively crazy compression (10-11:1 on 87 octane) and the engines just seem to be very hard on the plugs.

I still see wear on the small block plugs, but it's minimal.

No oil consumption is a good thing!

 

[tenderfoot]

In my old '79 years ago. I stript out most everything I could from the engine compartment. I liked to call it my office. I could get up in there sit on either side wheel well and the 350 was my desk. Anyway I was always changing spark plugs and oil. Experimenting with different gaps and oil wieghts. I had two or three different kinds of perfectly good sets spark plugs. Had fancy ones and heavy duty truck ones and on and on. Me and that engine we're pretty close. I could tell a difference in the little things and AC Delcos we're the best. I swear by Castrol too even though they sponsor Furd. Not that I'm a Nascar guy