aquaforce

I am getting ready to tune up all three of my 502 MPI engines and I wondered if the Iridium plugs would be an upgrade for this engine. I don't know what is in there now. I bought the boat last year and I want everything to be fresh for the season.

Any issues with Iridium plugs in the 502MPI?

Black Baja

iTrader: (2)

Absolutely not. You don't have near enough ignition to fire them. They are designed for coil on plug.

mike tkach

iTrader: (3)

according to several of the top brand plug makers you can use a iridium plug in your boat.they say it takes less voltage to fire the plug and that is the reason for the larger gap.the iridium alloy is hard and resists wear from the spark,that is why they last so long.they come from the factory pre gapped and it is not recommended to change the gap but if you are careful they can be re gapped.so if you really want to put them in your boat i say go for it but i see no real advantage to useing them in your boat.maybe BUP will chime in.this would be something he could answer better than me.

3pointstar

If BUP offers a comment. I would like to know about the application in a pure stock 7.4 MPI 310 hp (year 2000). I was thinking of changing out plugs wires and distributor cap this spring.

Thanks

3 pointstar

BUP

iTrader: (9)

the correct answer is all marine engine manu's recommend Iridium spark plugs for the past X amount years. Even outboards. Iridium is a very hard metal so the spark plug manu's fine wire it to help with spark energy. The electrode is very small in diameter and you have to watch out checking the gap and watch out what gap tool you use. (You do not want to bend or damage the fine wire electrode).

Also it is really not recommended to reset the spark plug gap with these type of plugs because possible damaging the very fine wire electrode. If you have to regap, it should be done very carefully.

Actually silver is the best electrical conductivity there is, next I believe is copper. They can make that thicker in diameter to help with electrode wear. They are very soft metals so they wear alot faster than Iridium. Hence the reason why Iridium are so popular now is because of less spark plug changes.

Everything today needs to be a resister type spark plug as well because of the electronics, ignition components and ECM's.

Here is just one example of an NGK Iridium spark plug that Merc uses for the V8 MPI 350 with spark plug wires and the HVS. Part number 14 in diagram and is NGK ITR4A15 laser Iridium. NGK has been laser welding the fine wire for a more precise made spark plug among other reasons.

BUP

iTrader: (9)

Here is the link showing what Mercruiser recommends with the Iridium NGK. Check it out number 14 in the diagram and in the parts list.

http://www.mercruiserparts.com/Show_...ion+Components

BUP

iTrader: (9)

for the 7.4 MPI mercruiser recommends NGK BPR6EFS I see no need to run any other plug for that app. This is NOT an Iridium spark plug.

Black Baja

iTrader: (2)

Iridium does not conduct electricity as well as copper. I would never use and iridium tipped plug unless the engine had an ignition that was designed to run it. The only advantage to running iridium is it lasts longer.

BUP

iTrader: (9)

for the 502 MPI I see no need to run the Iridium either. Mercruiser really does not list using them for 2000 and back years. Just some added info.

NGK spark plugs are really great plugs but not recommended for every marine engine. OMC use to recommend Champion and so did SOME Volvo Penta apps - Even put out SB's about missfires using NGKs in those apps. Just saying

BUP

iTrader: (9)

I was just posting OEM info as you said marine apps do not use Iridium and for coil on plug apps only. 2001 and up many marine apps are calling for Iridium and or Platinum or even double Platinum spark plugs.