Spark Plugs And Heat Ranges

[MikeInCtown]

Some of you may have seen my posts in the engine area asking about plugs and mileage drops. The short story is that after I changed my plugs my mileage at least on the highway dropped like 2mpg on average. Replaced oe plugs with A/C #41-985 which is the OE replacement. new plugs developed a carbon layer on them at the thread base where it goes through into the combustion chamber within 500 miles. Nothing abnormal on the electrode or porcelain though. All plugs are like this.

 

Over the weekend I looked up some NGK and Denso plugs. The NGK plugs range in price from $7 to $12 for the Iridium ones (IX iridium or the Laser Iridium LL) the Denso plugs Are $6.50 or $12 for either the IT16 or ZTJ16R10 plugs.

 

The NGK plugs along with autolite and Champion premium plugs are listed as a heat range 5 while the Denso plugs are listed as a heat range 16. I know manufacturers all rate their stuff differetly, but is it possible that the oe A/C plug used to be a hotter plug but that the part number has somehow changed to a lower heat range? I'm also wondering if I would still get the carbon buildup if I went with the Denso plugs with the supposedly hotter heat range. I'd hate to waste the money on more plugs considering I just changed them 2,000 miles ago, but if the Denso ones work better I'll just return the A/C plugs under warranty. Also thinking about changing one bank with Denso and monitoring for fuel trim and such to see if there is any difference.

 

Mystified.

 

-Mike

[REV353]

Some of you may have seen my posts in the engine area asking about plugs and mileage drops. The short story is that after I changed my plugs my mileage at least on the highway dropped like 2mpg on average. Replaced oe plugs with A/C #41-985 which is the OE replacement. new plugs developed a carbon layer on them at the thread base where it goes through into the combustion chamber within 500 miles. Nothing abnormal on the electrode or porcelain though. All plugs are like this.

 

Over the weekend I looked up some NGK and Denso plugs. The NGK plugs range in price from $7 to $12 for the Iridium ones (IX iridium or the Laser Iridium LL) the Denso plugs Are $6.50 or $12 for either the IT16 or ZTJ16R10 plugs.

 

The NGK plugs along with autolite and Champion premium plugs are listed as a heat range 5 while the Denso plugs are listed as a heat range 16. I know manufacturers all rate their stuff differetly, but is it possible that the oe A/C plug used to be a hotter plug but that the part number has somehow changed to a lower heat range? I'm also wondering if I would still get the carbon buildup if I went with the Denso plugs with the supposedly hotter heat range. I'd hate to waste the money on more plugs considering I just changed them 2,000 miles ago, but if the Denso ones work better I'll just return the A/C plugs under warranty. Also thinking about changing one bank with Denso and monitoring for fuel trim and such to see if there is any difference.

 

Mystified.

 

-Mike

[MikeInCtown]

Don't know why you quoted without a response but I guess it was a mix up. Anyway, i kind of realized that a lower number indicates a hotter plug. So unless the Denso numbering system is way off from all others I think it may be slightly different. I have also found that they recommend replacement at 30,000 miles even for their expensive ass plug. I think I'm going to give the NGKs a try as they are pretty cheap locally compared to mail order.

[REV353]

Each manufacture has there own numbering system, some use a lower number for heat and others use a higher number for heat. Did you replace the wires too?, do you have a cap and rotor?, have you ran any injector cleaner?. I always replace the wires with the plugs and cap and rotor if it has it. Iridium plugs are the way to go, get the lowest ohm wires you can afford, if your not sure about something call Summitracing and they will help and get you the parts you need if you so choose.

[REV353]

Don't know why you quoted without a response but I guess it was a mix up. Anyway, i kind of realized that a lower number indicates a hotter plug. So unless the Denso numbering system is way off from all others I think it may be slightly different. I have also found that they recommend replacement at 30,000 miles even for their expensive ass plug. I think I'm going to give the NGKs a try as they are pretty cheap locally compared to mail order.

 

 

I just went with Autolite Iridium plugs about 3k ago, I also went with Taylor spark plug wires that are 45-50 ohms per foot, under $60, the spark plugs i bought from a local napa being they were 40 cents cheaper per plug. Cheap is not what you want to do, save some cash and get the good stuff, I was getting 8-9 mpg in my 8.1L before and now I'm getting 10.5-11.9, I got 12ish once.

Hit the wrong button b4

[CapitalTruck]

OEM replacement plugs (the ACDelco's you mentioned) combined with new OEM ACDelco wires provided me with smoother idle and no mileage decrease after replacement atg 97k miles. You didn't happen to mess with the gap of the plugs did you? They come "pre-gapped" to where they should be.

[MikeInCtown]

OEM replacement plugs (the ACDelco's you mentioned) combined with new OEM ACDelco wires provided me with smoother idle and no mileage decrease after replacement atg 97k miles. You didn't happen to mess with the gap of the plugs did you? They come "pre-gapped" to where they should be.

 

Didn't touch a thing. one of the plugs got dropped and I re-gapped and put it into an easy to get to cylinder. I replaced it the next day with a brand new one. That was a quick $7 lesson into making sure you don't tilt the box. I thought maybe the replacement set of wires had something wrong with them so I bought another set of actual OEM wires with the new boot protectors. Same deal. I may get a set of MSD wires from summit if they send me another coupon as they'll be cheap enough then to try out.

 

I know I've posted on this many times already but it's just one of those things eating away at me because everything ran perfect before and should run perfect now with new parts. The carbon buildup on the thread ends lead me to believe too much fuel being injected and or incomplete burn.