Colder than Stock Plugs

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spf182

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Will installing colder than stock plugs on a stock engine cause any damage or negative effects?
I have some plugs for my 3.0 Ford Ranger laying around but they are a 12 heat range instead of the stock specified 32 - I think they are one or two ranges colder.
 
Carbon buildup is the likely result. If you drive your car between normal and sporty, and if the engine isn't modded, I suggest you stick with the OEM recommendation. Colder plugs are really for modified engines or engines that see track use.

You can get Beru spark plugs that cover two heat ranges, but that's really besides the point, because you'd like to use the spark plugs you already have.
 
It is funny how the meaning of "hot" and "cold" plugs is ofter misinterpreted WRT their heat range. Hotter plugs runn cooler in the combustion (more prone to fouling) due to their higher heat transfer potential. Colder plugs run hotter in the combustion chamber due to their lower heat transfer potential. It is opposite what most shade tree mechanics might lead you to believe.
 
Correct me if I'm wrong, but colder then stock NGK plugs that I use are just shorter then stock. They stick less into combustion chamber, and therefore have better heat transfer potential. But they do run colder...
 
A quick inspection of a plug should tell if it's heat range is correct. The possibility of engine damage due to a cold plug is nil. I grew up juggling carb jets and plug heat ranges on aircooled engines to the point that it became as routine as setting valve lash. One thing that a lot of people don't know is that a plug that sticks further or less further into a combustion chamber causes an advance/retard in actual timing that has nothing to do with timing settings. Just one more thing that needs to be taken into account.
 
Go ahead and use them.

Stock plugs have to be warm enough that they don't foul during the many cold starts and short trips between the factory and dealer delivery.

Worst thing that can happen is they'll foul, but an "italian tuneup" will fix that.
 
Simply put: Hotter plug burns colder, colder plug burns hotter.

As johnd says, it becomes a routine exercise in certain applications. it is basically a fine-tuning thing and will not remedy a mechanical problem.

The thing I remember was using colder plugs to offset rich-running engines where re-jetting didn't quite completely do the trick. Not much of an issue anymore with fuel injection these days...
 
quote:
It is funny how the meaning of "hot" and "cold" plugs is ofter misinterpreted WRT their heat range. Hotter plugs runn cooler in the combustion (more prone to fouling) due to their higher heat transfer potential. Colder plugs run hotter in the combustion chamber due to their lower heat transfer potential. It is opposite what most shade tree mechanics might lead you to believe.
Click to expand...
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A hot spark plug sheds, due to its larger ceramic insulator near the tip, less heat and will run hotter and foul less.

A cold spark plug has a smaller ceramic insulator near its tip and will shed more heat and run cooler, but will tend to foul more.
 
"Go ahead and use them. . . . . Worst thing that can happen is they'll foul, but an "italian tuneup" will fix that."

^ ^ ^ ^ ^ First of all don't hang around guys that say stuff like that.
rolleyes.gif


Use the factory recommended spark plugs.
 
I grabbed the service manual for my Geo Prizm about this. "Normal [spark plug] service is assumed to be a mixture of idling, slow-speed and high-speed driving. Occasional or intermittent highway driving is needed for good spark plug performance. The higher combustion temperatures generated during highway driving burn away carbon and oxide deposits that have built up from frequent idling or continuous stop-and-go driving."

"A spark plug one step higher/hotter in heat range might deliver longer service life than the spark plug recommended for almost exclusive city driving. Conversely, a spark plug one step colder than recommended will perform better for continuous high speed driving."

So basically it's said right there that colder plug means it runs a colder combustion chamber.

"There are three rules to follow when selecting spark plugs for an engine in good condition:
1. Select a spark plug with the specified heat range.
2. Should the spark plug overheating occur, choose a spark plug that is one heat range lower than the specified heat range.
3. If fouling is a problem, select a spark plug that is one heat range higher than the specified heat range."

I hope this helps. It makes me want to try a step colder plugs in my own car as I've noticed some pinging that I hear when things are hot driving in the city after coming off the highway and I rarely idle or have trips that don't involve a stretch of highway. Could a slightly cooler combustion chamber make a slight change in oil consumption perhaps?

If you want to try it, I would recommend pulling them and checking for carbon deposits after driving with them after a few hundred miles to see how they are doing. I'd verify that it is only one heat range in difference though as more than one could cause issues.
 
quote:
So basically it's said right there that colder plug means it runs a colder combustion chamber.
Click to expand...
That would be a misinterpretation. A colder spark plug simply sheds more heat and remains colder. The effect on combustion chamber temps remaining cooler must be near zero.

The spark plug heat range must match the driving conditions. The spark plug must get hot enough to burn off deposits, but it must not get too hot, or pre-iginition and detonation may occur. Luckily, today's spark plugs have very wide heat ranges, and deviating from the suggested heat range is necessary only in extreme cases (modified engine, extreme low or high ambient temps, lots of short distance driving and only high speed driving).
 
what is you have high NOX emmissions without an egr valve, would using a colder plug lead to less heat in the combustion chamber and therefore less nox? what about just gapping it shorter, wouldnt that make it colder too? smaller spark...
 
quote:
what about just gapping it shorter, wouldnt that make it colder too? smaller spark...
Click to expand...
no, because the heat flow path from the tip to the threads where it screws into the head (this is where it has to transfer it's heat to) is unchanged. All you do in reducing the gap is reduce the potential required to jump that gap. You do this if you have a (relatively) weak ignition, or if you are using a fuel that is generally harder to ignite, eg LPG. It has absolutely no effect on the plug heat range.
 
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