Ive read a few forums about what spark plug is best for a 4.0L Cherokee. But im confused on it all. Every forum ive read says to use Champion RC12YC. But i took mine out and theyre Champion RC12LYC which has about a quarter inch longer nose. And the sticker on the frame of the jeep says RC12ECC from the factory. All are Champions which is what im going to use. I was wondering why people are putting in the shorter RC12YC and what difference the shorter or longer one might make?

 

The longer and shorter 'noses' reflect the heat range of the plug. I'd guess that's true for the numbers as well. So, if your old heep is running up a few thousand miles, and the plugs look 'ok' but maybe a little dark looking, you can run a 'hotter' plug so they stay cleaner. Probably a chart somewhere on the net.

 

Thanks. I found a chart at http://www.championsparkplugs.com/sp...osch%29&mfid=2. So youre saying the longer one is hotter or the shorter on? Ive seen that the longer RC12LYC is used in dodge vipers.
Or the '12' is the heat range according to the chart?

 

If i remember right, the hotter ones are longer.. I only ever changed the heat range of the plugs on my old kawasaki 2-stroke.. hotter plug burned off more oil so they fouled less often. I don't remember for sure which was which as far as hotter vs colder, but the numbers told.. went from bp8's to bp7's 6's etc. lower number, hotter plug. I wouldn't go hotter on your jeep as it can damage an engine

 

p.s. I would just use the Jeep recommended plugs.. maybe the PO put those in there for who knows why.

 

Do you really think the engineers that designed the engine were crazy when they put the type of plug on the sticker?