Spark plug choice
Discussion
I've finished the rebuild of my 106 GTI Tu54jp engine.
It runs with no knocking, head gasket or oil leaks, however it sounds like the plugs have fouled, as its mostly done idling whilst I've been diagnosing various issues.
The engine is standard, but mapped (more fuel/air), but I am running NGK 7 spark plugs, these are a hotter plug than the standard plug for the car - the NGK 6.
My assumption is that the hotter plugs don't really like the idling, hence the rough running. ( it sounds like its trying to clear its throat).
I am testing the car for the first time at Mallory next week, I have bought a set of replacement NGK 6 spark plugs.
I am expecting the following to occur:
Existing 7 plugs clear them selves after some hard lappery.
They don't clear, but I clean them by hand, and then run fine.
I clean them, and then they foul up again despite hard lappery
At which point I'll swap in the '6's and see what they do.
Is there anything else I've missed? Is the above a reasonable course of events for my test.
I also have a spare coil pack I may swap in, if still no joy.
It runs with no knocking, head gasket or oil leaks, however it sounds like the plugs have fouled, as its mostly done idling whilst I've been diagnosing various issues.
The engine is standard, but mapped (more fuel/air), but I am running NGK 7 spark plugs, these are a hotter plug than the standard plug for the car - the NGK 6.
My assumption is that the hotter plugs don't really like the idling, hence the rough running. ( it sounds like its trying to clear its throat).
I am testing the car for the first time at Mallory next week, I have bought a set of replacement NGK 6 spark plugs.
I am expecting the following to occur:
Existing 7 plugs clear them selves after some hard lappery.
They don't clear, but I clean them by hand, and then run fine.
I clean them, and then they foul up again despite hard lappery
At which point I'll swap in the '6's and see what they do.
Is there anything else I've missed? Is the above a reasonable course of events for my test.
I also have a spare coil pack I may swap in, if still no joy.
Dynion Araf Uchaf said:
I am running NGK 7 spark plugs, these are a hotter plug than the standard plug for the car - the NGK 6.
They are a colder plug. If they are too cold for the use the engine is getting that would lead to plug fouling problems. If it was me I'd want clean plugs when the car is being driven in anger. Unless it's especially awkward changing the plugs, consider fitting clean 6s now and be prepared to change to clean 7s at the track if you get overheating symptoms.
Boosted LS1 said:
7's are a colder plug then a 6 hence why they may be fouling. Your reasoning is 'on track' :-)
according to the web Edited by Boosted LS1 on Wednesday 12th October 15:54
NGK plugs are hotter the higher the number. I think it's one of those situations where there has been no standardisation as to which direction the number should go in terms of temp so different plug manufacturers do different things.Unless you know for sure that is not correct?
GreenV8S said:
They are a colder plug. If they are too cold for the use the engine is getting that would lead to plug fouling problems.
If it was me I'd want clean plugs when the car is being driven in anger. Unless it's especially awkward changing the plugs, consider fitting clean 6s now and be prepared to change to clean 7s at the track if you get overheating symptoms.
easy enough to do. But see my last post. I reckon I should clean the 7s, then swap into 6's if no joy.If it was me I'd want clean plugs when the car is being driven in anger. Unless it's especially awkward changing the plugs, consider fitting clean 6s now and be prepared to change to clean 7s at the track if you get overheating symptoms.
Dynion Araf Uchaf said:
easy enough to do. But see my last post. I reckon I should clean the 7s, then swap into 6's if no joy.
All you've done is map it? I'd be surprised if that increased temperatures far enough to need a colder plug grade. You might need that if you've added forced induction but your post doesn't suggest you're anywhere near that sort of change. If you fit clean 7s now, you might well find they're fouled again by the time you get on track.GreenV8S said:
All you've done is map it? I'd be surprised if that increased temperatures far enough to need a colder plug grade. You might need that if you've added forced induction but your post doesn't suggest you're anywhere near that sort of change. If you fit clean 7s now, you might well find they're fouled again by the time you get on track.
Assuming we are on the same page for which number is hotter. Then I will put the 6s in and that should cure this particular problem. As they are standard for the car according to NGKDynion Araf Uchaf said:
Assuming we are on the same page for which number is hotter.
If NGK documentation disagrees with me then I'd trust NGK over some internet rando, but the NGK plugs I use all follow the convention that a higher number is a colder plug and I would expect NGK to use the same convention for all their plugs. For example: https://www.ngk.com.au/technical_info/heat-range/StescoG66 said:
Always wondered, other than fouling what are the longer term implications of running a hotter plug?
Equally a cooler one.
The plug heat range refers to the temperature that the plug electrodes operate at. This varies hugely depending on engine load and mixture. If the plug is too cold it won't burn off surface contanation and will eventually get so contaminated that it won't fire cleanly. The problem is most likely to start when the engine is cold and lightly loaded. If the plug is too hot the the electrodes can suffer heat damage and erosion, and may even get hot enough to cause pre-ignition. The problem is most likely to start when the engine is heavily loaded, especially if it runs lean under load.Equally a cooler one.
These aren't really long terms effects - if there's going to be a problem it can manifest in a few minutes or even seconds.
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