I've changed the spark plugs in a car about 3 times in the last 30 years, and not once have I noticed a difference.
The spark plugs in my present vehicle (3 liter 2000 Camry) have over 350,000 km on them. The car runs perfect and I still get the same mileage out of it as when I bought it almost new.
I haven't even taken the plugs out to adjust the gap in all that time. All I've done to that engine is change oil and filter every 10,000 km and timing belt every 100,000 km.
Anyone else agree it's a waste of time to change spark plugs, unless there is an obvious problem?
No, it's not a a waste of time. If you don't change your plugs at about 100000ks your gonna put extra stress on your electrical system. Like you your coils, dizzy, and charging system. Because the it takes more energy to jump the worn out gap.
If that fails it'll cost lots more than 4, 6, or 8 spark plugs.
Select to expand quoteHarrow said..
All I've done to that engine is change oil
Why change the oil? I only top mine up. last time I changed it I didn't notice a difference in mileage or performance, so i figured it why do it. 
I would say that modern cars don't wear plugs out anywhere near as much as older ones.
Before fuel injection, mixtures would be running lean, and running rich depending on so many things. I think it was the lean mixtures that eroded the plugs, and the erosion was why you had to regap them.
Now, the mixtures should be spot on and no car should be running too lean for any length of time.
Almost all cars now have direct ignition systems where there is a coil per cylinder or pair of cylinders, so the spark energy is much better and likely to fire even through a fouled plug.
In response to Spocktek's comment above, I would guess most cars don't have distributors any more, and a lot of them don't even have HT leads, using coil in plug (I think that's what its called). Modern charging systems have a lot more capacity than in the past. In the old days, a 30amp alternator was pretty normal. Now, they seem to be around 110 to 130amp to cope with the demands of the fuel injection system and everything else.
It's a good idea to change brake fluid, coolant, auto oil, and diffs.
You won't notice any difference in mileage but you will notice a difference
In the repair bill!
Select to expand quoteDezman said...
It's a good idea to change brake fluid, coolant, auto oil, and diffs.
You won't notice any difference in mileage but you will notice a difference
In the repair bill!
The one time I bought a new car, they had 'brake fluid flush' on the service schedule, and what do you know, they changed the air filter, oil, and oil filter, but never changed the fluid. I think its just another thing where they should do it, but it won't have any effect at all or for a long time that they won't see the fault come back to them.
Coolant is a good one to replace as with such a mixture of metals in the cooling system, corrosion of the aluminium radiators is common when the coolant 'wears out'.
Ford seem to have this 'sealed for life' idea with their auto transmissions, and thus no filler tube. I think this idea gets them through warranty, but in my own experience the gearboxes ran better once the fluid was changed.
Diffs I am not so sure about. I think it sounds like a good idea in theory, but am not sure you would see the effect unless you ran the car for quite a few hundred thousand kms.
In response to Spocktek's comment above, I would guess most cars don't have distributors any more, and a lot of them don't even have HT leads, using coil in plug (I think that's what its called). Modern charging systems have a lot more capacity than in the past. In the old days, a 30amp alternator was pretty normal. Now, they seem to be around 110 to 130amp to cope with the demands of the fuel injection system and everything else.
They don't have the old school mechanical dizzys but they do have electronic a distributor.
What else is gonna tell the plug when to fire??
Select to expand quoteSpocktek said..
In response to Spocktek's comment above, I would guess most cars don't have distributors any more, and a lot of them don't even have HT leads, using coil in plug (I think that's what its called). Modern charging systems have a lot more capacity than in the past. In the old days, a 30amp alternator was pretty normal. Now, they seem to be around 110 to 130amp to cope with the demands of the fuel injection system and everything else.
They don't have the old school mechanical dizzys but they do have electronic a distributor.
What else is gonna tell the plug when to fire??
It's not a distributor then. A distributor, based on its name, distributes the spark generated by the coil to each spark plug. In a multiple coil system, either a coil per cylinder or one per pair, the coils are connected directly to the spark plugs. The coils are switched by some type of transistor, but there is no distributor. Each coil has a separate switching transistor, and in theory could all fire at the same time, not that that's required 
Select to expand quoteHarrow said..
I've changed the spark plugs in a car about 3 times in the last 30 years, and not once have I noticed a difference.
Me neither, run a couple of Commodores to close to 400,000km, rarely if ever changed the plugs, never the diff or gearbox oil. Diffs and gearboxes were all going fine when they were finally sent to the wreckers. Engines got a bit tired even though the oil was regularly changed.
Select to expand quoteSpocktek said..
What else is gonna tell the plug when to fire??
It's this new fangled thingy called a computer
Btw, modern engines run MUuuuuch leaner than older engines (tuned properly). They're able to due to this new fangled thingy called a computer.
Select to expand quotedinsdale said..Spocktek said..
What else is gonna tell the plug when to fire??
It's this new fangled thingy called a computer
Btw, modern engines run MUuuuuch leaner than older engines (tuned properly). They're able to due to this new fangled thingy called a computer.
I had a VN commodore 5 speed and it used to throw a 'running lean for too long' code, or something to that effect, when cruising in 5th on the highway. It had a burnt exhaust valve when I got it. I suspected it was the running lean condition that caused it, but once I replaced it, it never had a problem again.
