rc12lyc on 4.0 RENIX.

Hi, folks, just wandering, can i use champion's Spark plugs rc12lyc on a 1988 cherokee? The Haynes manual indicates rc9yc, but the previous owner of my rig got the rc12lyc, those are a little bit longer, hence my question.

thanks in advance.

I don't know the exact answer, but if the plugs are enough longer to stick into the combustion chambers, they may affect compression and flow in the chamber, and if they are the wrong heat range they might either foul or overheat and cause knocking. Spark plugs are pretty cheap and they last a long time on an XJ.

The rc12lyc is the H.O. OEM plug. I don't think you will have a problem running them but I would probably switch to the rc9yc anyway. The H.O. plug is slightly hotter and is an extended electrode gap and core nose projection vs. the RENIX standard projection core nose.

I use the RC12 plugs on my 4.0L 1990 renix with no problems