…but are they the same brand, and the same model number, that Toyota specifies in your Owner’s Manual? Japanese carmakers usually list a specific model number for both NGK and Denso spark plugs, and the use of any brands/model numbers other than those two can produce undesired results.
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VDCdriver, I cannot answer that question. At that time, I did not pay attention to such details except that they were a close equivalent to OEM. Also, as I mentioned, the mpg was fine for a year and a half after the spark-plugs replacement. After trying out the good suggestions from this blog one at a time, I will change the spark-plugs too if they do not result in improved mpg.
Why would plugs, other than the ones listed in the owners manual, produce undesirable results. As long as the plugs fall within the manufactures specification he should be just fine.
I assume that manufactures list the brand and model number they use as a matter of convenience for the consumer and to entice them to buy that brand. They surely would not list ALL available brands and models that fall withing their specifications.
@kurtwm2010 Even if the plugs meet the manufacturer’s spec, there are small differences in spark plug design that do, indeed, matter. Some cars are extremely sensitive to those differences.
My wife’s Saab has an ignition cassette that includes the coils and senses misfires using the plug as a “sensor” of sorts. Non-standard plug cause trouble codes where the OEM brand would not. I had a Honda S2000 that I installed Bosch plugs into. If I ran the car hard, the plugs would loosen even after being torqued with a torque wrench with no anti-seize. I got tired of that and replaced them with OEM plugs. No further problems with loosening.
Back in the day, those problems didn’t really exist. It was more about brand loyalty. These days, problems you MIGHT cause with non OEM plugs can be avoided by using OEM. It just isn’t worth the risk for someone not doing their own work.
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Many manufacturers of aftermarket plugs produce plugs that have the same physical parameters, heat range, and even platinum tips, but the overall quality of manufacture isn’t there and they fail early. I personally have had this problem. I’ll never use anything other than NGK or Nippon-Denso in Toyotas. Variations in electrode alloy, “treating” of the metal, electrode manufacturing process, ceramic, shell material, and other factors can definitely affect a plug’s longevity.
I don’t disagree with you or Mustangman.
One reason this came to my mind was that earlier this morning I purchase four NGK ZFR5F-11 plugs for my wife’s Acura. Those are the recommended plugs per the manual. I paid $2.49 a piece for them and they have a 30 days “warranty”. I normally would have purchased something of higher cost/quality and a better warranty, but I decided to follow the manual this time and find out how good/bad they are in the long run.
You can go back & edit your post OP if you like. Click on a button at the bottom that says “edit”. Besides the good advice above — not measuring correctly, engine operating temperature too low, coolant temp sensor malfunction, basic tune up needed – here’s some other things that can cause it
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change in driving habits. Are you doing more city stop and go driving now than before? More idling, waiting in traffic or for kids to come out from school?
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fuel pressure is too high , check fuel pressure and fuel pressure regulator
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air leak is allowing unmetered air into the engine, check for vacuum leaks and leaks in boots, hoses that are disconnected, exhaust system leaks
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pcv system problem. if nothing obvious is found on visual inspection, try replacing the pcv valve
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does the tailpipe have a lot of black soot in it? Any black smoke out the tailpipe when engine is running?