I'm shopping new spark plugs for my '87 Ram 50 with the 2.6L G54B engine, and noticed some odd discrepancies in the heat range specs depending on which reference I use.
First, note this spark plug heat range cross-reference/conversion chart (all other charts I've seen have identical data):
https://www.densoproducts.com/heat-r...ersion-chart-2
Next, this page does a pretty good job illustrating and explaining what heat ranges mean and what they do:
https://www.denso.com/global/en/prod...sic/heatrange/
Now, my truck's owner's manual specs the following plugs for both the 2.0L G63B and 2.6L G54B:
- Champion N9Y or RN9Y
- NGK BP6ES-11 or BPR6ES-11
- NipponDenso W20EP-U10 or W20EPR-U10 or W20EPR-S11
Trivia: The R in any of those indicates a Resistor plug to suppress EM noise from the ignition interfering with the radio and any other electronics, and the -11/-U10/-S11 suffixes just indicate a gap size pre-set at the factory, so nevermind all that for now.
The key thing here is the numbers in the middle, representing the plugs' heat range; all of those plugs have equivalent heat range specs according to the chart:
Champion 9 = NGK 6 = Denso 20
Here's where the weirdness comes in. On every major parts-vendor site when I look up parts for my specific year/make/model/engine, they all list various Denso plugs with a 16 heat range among the other Champion 9, NGK 6, and Bosch 7 plugs; Denso's own corporate site only lists 16s for my truck as well. According to the chart, a Denso 16 should be a full step hotter than all the other plugs these vendors list for my truck.
Checking the Haynes manual just added to my confusion; they spec NGK 6 plugs for the 2.0L but NGK 5 plugs for the 2.6L, which latter would be equivalent to... a Denso 16.
My reason for going down this rabbit hole was that this past February when I went to take my truck in for its annual emissions test, it was suddenly misfiring when I started it up, but with fingers crossed I kept driving to the smog station anyway hoping the misfire was just a cold-start fluke that'd clear up by the time I got there. Lo and behold it did, and passed the smog sniff (just barely) on the first try. Good for another year, whew!
When I got home again, I decided to check the plugs and found one had a cracked insulator around the center electrode. That would explain the sudden misfiring, reckon the ceramic must have expanded with heat as it warmed up and sealed up the crack enough to eliminate the misfiring during my smog check. I swapped back to an old set of plugs I had lying around, and it started up and ran smoothly ever since.
Last week or so, it suddenly started doing the same thing, misfiring on cold starts that went away as it warmed up. I hadn't fiddled with anything else to explain that, so I'm suspecting a similar issue as before but haven't pulled the plugs yet, since this is my only operational vehicle atm, and I want to have a fresh set of plugs ready at hand first.
Reading up on cracked insulators, I've read one cause can be running a plug that's too hot. I've also read that it's better to err on the side of running a too-cool plug than a too-hot one, as the latter can cause damage, whereas the former just takes longer to warm up to operating temperature and can reduce power and economy.
Has anyone experimented with different spark plug heat specs, or have any experience comparing heat ranges NGK 5 vs. 6, or Denso 16 vs. 20, to notice any differences in how your truck ran with both?
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