sb5walker

Nope, the plug temperature has no effect on combustion temp - just on how hot the plug gets. Definitely best to use the plug specified for the motor.

To cool combustion, make sure egr is working (#1 cause of hot combustion is bad egr), run a bottle of Red Line SI-1 Complete Fuel System Cleaner or CRC's "Guaranteed to Pass Emissions Test Formula" through the tank (the only two products with polyether amine which is the only effective in-the-tank injector cleaner), make sure there are no vac leaks, either between the air meter and throttle body, or anywhere in the intake or in any vac hose, make sure the O2 sensor is a Denso in good condition and the connector is clean, and set timing to 5 deg btdc with jumper set on the 22re or 10-12 deg advance on the 3vze.

If you think the pistons and valves could be caked up with a lot of carbon, blow it out with water, per this post:
https://www.yotatech.com/forums/f116...l#post51124041

Yes, water really works:
http://www.files.thinksitout.com/Alt...f%20engine.pdf

xxxtreme22r

not on a stock motor, higher compression, turbo, supercharger, nitrous, yes. Rule of thumb for every 75–100 HP you add you go one step colder on the plug.

xxxtreme22r

Not according to NGK. http://www.ngk.com/charglossary.asp?kw=Heat+range

sb5walker

I think NGK's tech writers have misunderstood the situation - the heat that the plug removes is the heat of the electrode, not combustion temps. You will never see a 70 deg C lowering of combustion temps by going one step colder on a plug. That 70 to 100 degree difference, I guarantee you, is of the electrode. There just isn't anywhere near enough surface area on a plug to make much difference to overall combustion temps. Remember a plug doesn't add any heat to the combustion chamber - the heat comes from the combustion. The only heat the plug will remove from the combustion chamber is the heat that goes from the combustion chamber into the spark plug itself - and that's a minor percent of overall combustion temp.

http://en.wikipedia.org/wiki/Spark_plug

xxxtreme22r

OK now I get what they are saying here, put those two together.

Too hot of a plug may, however, indirectly lead to a runaway pre-ignition condition that can increase engine temperature. Think about it you add 75-100 HP to a motor and use stock heat range plugs. You wind up with the condition they are talking about and this is what NGK is talking about when they say lowing the combustion chamber temps.

You are not really lowering them but you are preventing it from getting 70°C to 100°C hotter because of pre-ignition.

Follow me? Me taking it out of context might have helped confuse matters.

sb5walker

You got me, I agree that too hot a plug can theoretically cause a hot spot that can cause pre-ignition (which is combustion that is triggered before the plug fires, as distinct from most types of detonation, which usually happen very shortly after the plug fires). And yeah, pre-ignition will cause higher temps. The most common cause of pre-ignition, though, is carbon buildup, which can glow red hot.

But, getting back to Ian's question about colder plugs helping with detonation, I think if he is using a stock spec plug and has a detonation problem, the cause of the detonation is not going to turn out to be the plugs. Much more likely to be combustion temps too hot because of clogged or malfunctioning EGR, mixture too lean (possibly caused by vac leak or clogged injector), or timing too advanced, or carbon buildup causing pre-ignition. If he's using a hotter-than-spec plug, though, you're right that the plug might be the culprit.

xxxtreme22r

I agree. sd5walker. High compression/Forced Induction is a whole other beast. There is no reason on a stock or mildly built engine to use a different heat range plug.

As far as carbon build up, that usually causes higher compression as well. But on an older motor it's hard to see it because of ring and cyl wall wear. So in a way it's more of a change in "quench" and I use that term real loose in this case.

THe carbon build up is one of those things I might be facing with my BMW with 245K on it right now. But till I get a compression gauge on the thing well...

irab88

iTrader: (4)

hmm... it's been a while since i did a tune-up. the last time, iirc, i put in bosch 4+ plugs (hey, my dad was buying, i'll get the expensive stuff). they're... ok. not worth the extra $$$. i think i'll replace them soon (by the way, what's a good plug life interval?) with oem denso's. i need to check the condition of them still. my last plugs had a nice orange crust on them.

i'll try the water treatment and the red-line cleaner sometime. looks promising.

thanks guys!

edit: here's that plug. an ngk

sb5walker

Is your coolant rusty?

Hopefully not, and that orange is from some strange fuel additive or some other weird thing. Kinda looks like coolant, tho.

The spec on replacing the plugs under normal operating conditions is 36 months/30k miles. With higher mileage and more oil burning, the plugs should be changed more often, maybe 20k miles? Let their condition be the guide. Based on the one in the pic, I'd change more frequently, but first you probably want to track down the source of the orange.

irab88

iTrader: (4)

i can assure you my coolant is fine. i think i did try an octane booster back then.

here's the plugs, as of 5 mins ago:

#1


#2


#3


#4


they all had a slight white crust
some things i noticed:
#1) nothing abnormal
#2) threads and base had oil, but none at the tip
#3) same as #2, but more oil
#4) same as #2, but less oil

sb5walker

I can't get pics 1 and 3 to load. #4 looks pretty white, probably running a bit lean, probably from a partially clogged injector. Only in-the-tank injector cleaners worth bothering with are the two that still contain polyether amine: Red Line SI-1 Complete Fuel System Cleaner (30-50% PEA) or CRC's "Guaranteed to Pass Emissions Test Formula" at 25-35%. Techron, Gumout Regane and BG44K used to contain PEA but no longer do.