gotsnowboards

So here's a debate as big as oil. I would like to know what everyone thinks with our inline tractor motors(yes I said it, I'll burn in tractor hell). What spark plugs do ya'll suggest. Both opinion and actual facts. NGK??

EZEARL

WTH,I'll bite.

Got my '96 XJ 4.0/auto in August of '08 with 98k miles from a friend I knew quite well who had bought it new. Quick check found the mpg at 13 on country roads. Pulled the plugs (the recommended Champion RC12LYC's) which turned out to be the originals as per the original owner. She said it always ran fine and she was right,it did. The center electrodes were almost even with the porcelain. Replaced them with Bosch Platinum 4's. Ran as good as before but with the mpgs going to 17 "city" and 21 on the highway. Thing was they only lasted not quite 30k miles when the mpgs plummeted back to 13mpg. I now have a set of the recommended Champions and all is good,for now anyway,although I lost a bit of gas milage going from 215's to 235's in tire size. Just waiting to see how long these plugs last. Story to be continued.

belvedere

I prefer standard copper-core Champion or NGK.

highmileage

I prefer using NGK, I have used Champion coppers and saw no change in the way it ran or burned fuel vs. NGKs'.
Currently I am using Autolite Iridiums, scored for 2$ each(good sale), and they seem to be working just fine in relation to NGK.
I do avoid Bosch they just flat out do not burn right.

Pelican

EZEARL, this is slightly off topic for the thread but pertinent to mpgs.

I also have 235's and used to have a percentage or mileage figure I used to calculate mpg with an unmodified odometer which I've lost. Could probably work it out with a comparison of the circumferences but just curious if you happen to have a figure readily available.

Potatowalker

Here's my .02: I've always ran the recommended Champion coppers, per the engine bay label on both the 96 XJ I had previously as well as my current 99 XJ. As long as they were in good shape and clean they never gave me any issues. I did find myself cleaning them more than once a year though. So recently I switched to Autolite single platinums and they seem to be doing just as well if not yielding a slightly smoother idle. I'm not sure if they'll last longer than the standard coppers or not. If so, I'll be using Autolites from now on. I've never used NGKs so can't comment on those.

salad

lol

Champion or NGK coppers. Champion P/N is found under your hood, or cross-reference it to NGK's V Power (copper resistor type) line. They're both cheap and good enough for guaranteed performance. By that I mean if your engine has problems with them, it's not your choice of plugs (could be defective still of course). Lots of people report problems with platinum, E3s, Bosch plugs, and so on.

Later models had a TSB issued by Chrysler superseding Champion plugs with NGK plugs on the distributorless ignition models. Apparently there were some reliability problems that surfaced with the waste-spark. There's some speculation that Champion had some QA issues but I don't know how much credence that deserves.

Personally with how dirty and sloppy most 4.0Ls are out there I wouldn't shell out for any fancy plugs. I'm also a firm believer in checking the plugs regularly as they're a good way to diagnose issues.

EZEARL

I did my mileage checks when I was running 215's. Never did an "official" mpg check with the 235's but I noticed right away a bit of loss in power and decrease in mileage numbers on my tripometer. Not much with either but noticeable
I lost yrs of info I had stored on all sorts of things when my computer crashed in Nov. One piece of info dealt with diff diameter tires and how to determine the diff for your speedometer. SIL is working on retrieving the all the lost info. Meanwhile if any one knows the formula Pelican and me would be grateful.

CCKen

A word or two about NGK & Champion plugs:

If you go to the NGK website and look up NGK plugs for your Jeep you will find that they list ZFR5N plugs for 1999 - 2001 Jeeps w/4.0 motors.

If you have an earlier Jeep (<99) you will see they list a FR5-1 plug. That is the wrong plug for your Jeep. FR5-1 plugs are for Chrysler and Dodge V8's.

You can use ZFR5N plugs in earlier 4.0's with no problem, as well as the Champion RC12LYC plugs. The ZFR5N plug is almost the same as Champion RC12ECC plug, the only difference being is the ZFR5N plug has a slightly cooler heat range than the RC12ECC plug. The RC12ECC plug is identical to the RC12LYC plug in having he same heat range, except that the RC12ECC plug has an improved design over the RC12LYC. Note the "CC" at the end of the RC12ECC plug number. This means Copper Copper. Copper Copper plugs have Nickle plated Copper ground electrodes and Nickle plated Copper center electrodes.

Pelican

EZEARL, thanks for the reply. Not the most critical info but nice to know as long as we go to the trouble to come up with accurate mpg figures.