I have 99k miles on my 99 XLS. It came with NGK multi-ground plugs which I jusy discovered are very pricey - $10 each from Amazon. I had a 99 Lexus RX300 with the same engine except it was variable timing.
What is the purpose of multi-ground plugs? Do I really need them? I can put it nice NGK platinums for just a few $ each.
I am not sure why, but the toyota scheduled maintainence guide says this: 1999 Avalon
120,000 Miles - 96 Months
Replace engine air filter Replace engine coolant Replace engine oil and oil filter Replace platinum spark plugs 1 Rotate tires
Inspect the following: Ball joints and dust covers Brake lines and hoses Brake linings/drums and brake pads/discs Charcoal canister 2 Differential oil Drive belts Drive shaft boots Engine valves Exhaust pipes and mountings Fuel lines and connections, fuel tank band and fuel tank vapor vent system hoses Fuel tank cap gasket Steering gear box Steering linkage and boots Transmission fluid or oil
The service manual which came with my car says 60k with a footnote that syas it is required for the Emission Warranty. My plugs look as good as new but I will have to replace tham once and I thought I would do it now. I know the sparkplug cylinder seals are leaking a little oil (started at about 60k) and I want to pull the plugs to see if I need to replace seals and valve cover gasket. Since it is a minor PITA to pull the plugs I may as well replace now. I will go with the narrow tip iridiums.
I think the main reason Toyota installed multi-ground is because of the waste spark ignition which will shorten the life of a plug. However, anything I put in will last way more miles than I will be driving on this car.
Some combustion chamber designs (such as a rotary motor) require that the spark plugs have the ground electrode placed to the side of the center electrode rather than below as on a traditional plug (see photo). This firing tip design tends to erode the tip of the ground electrode faster than a traditional plug. Erosion at these points creates a larger gap between the center and ground electrodes, causing plug misfire. Thus, by having more ground electrodes, you extend plug life. It is important to note that multi-ground does not mean multi-spark, there will still only be one spark at a time. Therefore, a multi-ground plug will not perform any better and may actually perform worse than a traditional plug, unless the engine is designed for a multiple ground plug.
My concern would be why the Avalon has side ground plugs? In particular, make sure the new plug you get doesn't protrude any further into the cylinder head. If it contacts the piston things could get nasty.
Dual-Ground Electrode Spark Plugs
Select Toyota models feature the Toyota Direct Ignition System (TDI), which enables spark plugs to fire twice as often. The system, introduced in 1994, creates a more efficient and cost-effective engine. Dual-Ground Electrode Spark Plugs feature a special design that delivers optimum performance and durability while maintaining the original recommended change interval.
I suspect the double grounded plug is just a way to increase the life of the plug and a good platinum plug should work similarly, albiet, not last as long....but I'm no expert.
Last edited by ImDisaster; 04-15-2010 at 04:55 AM.
The double ground is used because the 3 coil/3 wire ign system is called waste spark ignition. the plug is fired 2 times per cycle, once to light fire and once "its mate" cylinder is firing. Personally I'd use the proper plug.
The double ground is used because the 3 coil/3 wire ign system is called waste spark ignition. the plug is fired 2 times per cycle, once to light fire and once "its mate" cylinder is firing. Personally I'd use the proper plug.
What benefits do you see with the multi-ground plug?
Ok. All NGK and Denso platinum & iridium plugs can easily go 100k miles these days. In fact, Denso designed their iridiums to go 200k miles and based on what I experienced on our 99 RX300, they can do that. Do you see any advantages other than long life?
it sounds like you are trying to justify in your own mind to use the cheaper plugs. go ahead an try them, but seach the forum and hear it from others how their car ran like crap after using the single grounded plugs.
it sounds like you are trying to justify in your own mind to use the cheaper plugs. go ahead an try them, but seach the forum and hear it from others how their car ran like crap after using the single grounded plugs.
Not really. My 99 RX300 (RIP) had the exact same engine except it didn't have a waste spark ignition and it had VVTi. The RX came with Denso iridiums which I assume are superior plugs because of their small diameter tip. I am simply trying to understand why my Avalon, with the same engine, will run better with the multi-ground NGK's. Why didn't Toyota put the multi-ground NGK's in my Lexus RX300? The only benefit I have heard so far is life, but the NGK's surely will not outlast the Denso iridiums. Now you are saying the car will run like crap. Why didn't my RX300 run like crap? I like to understand the technical reasons for things. I'm not trying to justify a position or get in an argument.
Your Avalon has 3 coils and 3 wires causing it to fire each plug twice per cycle vs. your Lexus with 6 individual coils which only fires each plug once per cycle.
I would almost be sure it's a longevity issue......
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Toyota/Scion of Des Moines
(800)342-7045
Your Avalon has 3 coils and 3 wires causing it to fire each plug twice per cycle vs. your Lexus with 6 individual coils which only fires each plug once per cycle.
I would almost be sure it's a longevity issue......
Yep. That's what NGK says. Spark will jump to closest ground. It will wear until the other ground becomes closest and the spark will jump there.
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1999 Toyota Avalon
Replace engine air filter 
Ball joints and dust covers 
Linear Mode
