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Spark Plug Compatibility

A friend of mine has a 2002 Mitsubishi Galant with a 4 cyl engine. He installed some Bosch 4 prong (Platinum) spark plugs and said they increased his gas mileage significantly (better than what the factory specified). I have a 2006 Galant with a 4 cyl engine but when I called the auto parts store they said that Bosch 4 prongs are not compatible with my engine. What would happen if I put them in anyways? I don’t really understand how certain spark plugs can work with a 2002 Galant and not work with a 2006 Galant when they have basically the same engine. Can anyone help?

I replaced some badly worn plugs with the exact OEM replacement and got 4 mpg improvement. There is nothing special about the Bosch 4 prong plugs. Actually I’ve heard more negatives about them than positive.

I’d recommend putting in the exact OEM plug that is called for in the owner’s manual.

If a car maker could get 4mpg improvement just by using a different style spark plug, don’t you think they would do it???

I can’t believe how many different types and brands of spark plugs are on the market… It’s ridiculous. A big shelf-space war.

As everyone pointed out…You replace worn-out plugs with new plugs OF COURSE you’re going to get better gas mileage.

Stick with a good OEM type plug (probably NGK or Denso). I guarantee you that if your friend replaced those plugs NGK plugs his gas mileage won’t change one bit.

It really comes down to simple physics. Electricity will follow the path of least resistance. It makes no difference if there are 4 paths or 1 path. In order for those plugs to work the OEM type plugs would have to be MIS-FIRING. All the spark does is ignite the compressed gas in the cylinder.There is no way 4-prong plug will make one bit of difference in performance over a standard OEM plug.

Bosch plus use higher quality metals, don’t some metals conduct better than others, therefore increasing power and improving efficiency, or is it just marketing hype?

Pretty much marketing hype. The newer metals, platinum and iridium, wear less so the plugs can be left in the car longer. This is good if you have a motor that requires a lot of effort just to get access to the plugs. In most cases where access is relatively easy leaving the plugs in for 100K miles can make them very difficult to get out of the motor.

Mfg’s use the long lasting plugs so the cars will meet emission standards better as they age. The performance of any new plugs will be similar regardless of the metal used in them. Standard plugs need to be changed at about 30K miles while platinum can go 100K. Leaving a standard plug in beyond 30K will see a drop off in performance compared to platinum.

Your car is 4 years newer than your friend’s. Even if the basic motor is the same there can still be changes in the head, the shape of the pistons, the electrical system, and other differences which account for a plug for the older engine being incompatabible with the newer motor. Do not install a plug unless it is recommended for your car.

There’s only ONE metal that conducts electricity better then copper…and that’s Silver.

Platinum actually has pretty poor conductivity. What platinum gives you is LONGER lasting. It holds up 2-3 times better then copper plugs. And the plugs are NOT pure platinum. They’re copper with a platinum coating.

Your friend either had a poorly running car that was improved by new plugs (any new plug would help) OR he is suffering from the placebo effect.
If the car was apparently running well before the plug change then it’s the placebo at work.

The 4-prong Bosch plugs are nothing new. They’ve been around about 30ish years or so and as far as I know the original application was for certain models of air-cooled VWs. (F.I. Bus, etc.) My memory is real fuzzy as this is ancient history.

So yttrium and iridium spark plugs do not run even a little bit hotter than copper or platinum? If they don’t, then the spark plug companies are really scamming people, because iridium spark plugs are up to three times the cost of standard spark plugs.

What you’re buying with Iridium is longevity as MikeInNH pointed out. I recently bought a set of NGK Iridium IX plugs ($9 per). The plug tip is super small, it runs very hot (temperature wise) and this, coupled with the metal, makes them last a long time in service.

BTW- I bought the plugs to harvest the Iridium tips from them for a project at work.

Not really…they last 2-3 times LONGER then copper plugs. If you have someone replace the plugs for you…then just extending that change interval from 30k to 60k miles is going to save you far more then the cost difference.

Personally I like to use Copper plugs (NGK). I change them once a year (35k miles). I don’t like keeping plugs in there for much longer. As I remove the plugs I look for problems and correct them before they become big problems. Iridium plugs are designed to last 100k miles. There’s no way I’d keep a plug in an engine that long.

I have a 1958 issue of SPEED AGE magazine, and on the back cover is the following ad. “New Sparkplug Invention! Self-Cleaning, 21 Point Nickel-Cadium Sparkplug. 10 Horsepower Gain! 9 MPH Greater Speed! 15% Fuel Savings!”

Oh! And if you buy a set of these plugs, you get for free, The Reactor Drain Plug!!! What does it do? Why it destroys damaging engine acids that give you 100,000 miles without a major engine repair! Saves oil, gas, and repairs!

Even back in 1958, they were trying to scam people for these miracle products. Yet, I don’t see these sparkplugs on the shelf today. I wonder why?


OP, you seem to be assuming that a hotter plug means a hotter spark which then translates to better fuel mileage and power. It does not work that way at all.

If I happened to come up with any widget (spark plug improvement, water to gas device, or whatever) that would legitimately improve fuel mileage by say 1.5 MPG the last thing in the world I would do is run ads in Popular Mechanics or peddle it on the net.
The plans get buried in the desert, my house gets 24/7 armed security, and negotiations begin with world governments and makers of products with gasoline engines to make me the wealthiest guy in the world.

Tester’s post is pretty funny. I remember hearing about those Reactor plugs many years ago but had forgotten all about them.
A huge scam around here about 25 or so years ago was the Monroe Fuel Saver. They even opened up a brick and mortar storefront selling nothing but these and were in business for about a year or so. The longevity should say something about the pool of suckers.

I had to repair a couple of towed in cars that were fitted with these things. All it was was a vacuum valve located in the fuel line to the carburetor. The manifold vacuum operated valve “sensed when fuel was not needed and returned it to the gas tank until it was needed”.
Unfortunately, not only did they not work under this bogus scenario but also caused a few problems with gas actually making it to the carburetor.

Guess that’s one way of saving fuel; keep the gas away from the carburetor and don’t drive. :slight_smile:

I installed a “toilet paper” oil filter on my '67 Mustang that would filter the oil so clean you’d never have to change it. That was not really the claim but something almost as ludricous. I bought the thing, don’t think it did anything special and went back to standard filters eventually. Lot’s of claims for lots worthless products and I have ignored them all for years now.

Why does pointing out that if these products worked that they would be on every car seem to fall on deaf ears? In conversation with others about these products I point out the “wealthiest man on Earth” situation and people just don’t get it. It is the best argument why a scam is happening.

There’s a sucker born every minute.

Iridium and Platinum DO make a hotter spark. It has nothing to do with conductivity or resistance, it has to do with area. Because the Iridium and Platinum erode less, the point on the cathode end of the spark plug can be made smaller. Iridium can be made the smallest as it is the most resistant to erosion. The smaller the point, the stronger the corona created around it and therefore, the hotter the spark.

This is not to be confused with the heat range of the plug. The heat range is determined by the insulation around the tip. Not enough insulation (a colder plug) and you may get deposits that build up on the tip. Too much insulation and the tip can burn off. You need the heat range that suits your engine and your type of driving.

As for as the four prongs (anodes) used on the Bosch +4. The anodes on this plug are iron. The plug will last longer only because the are four anodes to erode instead of one.

A little more background here. All anodes are iron. Early Platinum plugs had one iron anode and a Platinum or Platinum plated cathode. On copper plugs, the cathode wears faster than the anode. The Platinum plugs would last longer because only the anode eroded, Multiple anodes last a little longer and do have the advantage of not shadowing the fuel air mixture. The worth of that feature is debatable.

The 100,000 + mile plugs have either a Platinum or Iridium cathode and a Platinum disc welded to the anode. Now both the cathode and anode will erode much less. The Iridium plug can have a smaller diameter cathode for a slightly hotter spark and it can last a little longer than the “Double Platinum”.

Most, if not all, Double Platinum and Iridium plugs have a plating on the threads that keep them from seizing to the Aluminum heads. Early 100,000 mile plugs didn’t have this plating so these plugs have developed the reputation for seizing. If you do use a plug that is un-plated, you can use an anti-seize compound on the threads, but I’m not sure that anyone makes an un-plated, long life plug these days. The Bosch +4 is un-plated I think, but they do not claim 100,000 mile longevity.

Thanks for a great informative thread here. I use OEM plugs but don’t really believe the manufacturer makes much difference for the same type plug.

NO manufacturer makes their own sparkplugs.

Go ahead if you like hammering noises or the sound of the starter. The biggest tall tales come from friends and opinionated bystanders. Don’t believe anything you hear about spark plugs making great improvements.