using multiple brands of spark plug=

[Chris]

Hi,
I’m working on regaining some MPGs. I have a 94 Dakota 3.9L. I had it up to 19mpg for a tank or so now its back down to 14-17. All the electrics are less than 18 months old. Brakes are same age, transmission is rebuilt in the last year, new tires in the last month, no codes.
I will change the oil soon.
I looked over Eric’s MPG pages and aside from the oil and possibly an after coil voltage leak IDK what to look at. Then I remembered that I never got matching plugs to replace the two odd ones. (I broke two at different times while doing tests and just replaced them with what was available at the store i Was in.) Can that be the problem? Should I just replace all 6?
Thank You

Topic

[college man]

All 6 of the correct brand for the truck. no mix and match.

[Chris]

Thank You
Edit; for anyone with the same rig the dealer says the recommended brand is Champion. If I remember correctly the exact type is on a sticker under the hood.

[Mike]

I think we’re merging into mythological territory. As long as the heat range, the plug reach and the seating geometry are all the same and appropriate for the application, and all the plugs share the same electrode configuration and are gapped accurately, there shouldn’t be an issue.

It’s not like the engine can read the manufacturer’s name stenciled on the insulator.

Having said that, it’s a good idea to use all the same plugs. It eliminates any inaccuracies in cross-referencing claimed heat ranges from different manufacturers.

[Chris]

I was of the same opinion as you Evil-i but Eric has a section on MPG’s and one point he makes is that you should use the manufacturers recommended brand. I was asking just to get an opinion on the mixing of brands as I wanted to eliminate the possibility that this is why my MPG’s have dropped. The odd ball plugs one was an NGK a perfectly good brand and the other was an E3.20 a brand I never heard of that had a forked tang and claimed to work better than normal plugs. They were both warn much less than the older dealer rec plugs.
I’ve bought and installed them. On the plugs I removed, one was gapped to narrow and a couple others were too wide all seemed worn about the same at the tang but some had more black on the threads than others. I broke one of the new ones putting it in so I cleaned up the best one of the correct brand with a wire brush, gapped it right then put it in an easier hole to replace it from.

[Author]

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