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Old 04-17-2010, 02:14 PM   #1
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Default Choosing the right glow plug..?

I have a mixture of small and big block engines in my vehicles and and have always used whatever glow plug came with the engine. I also always run 20% nitro fuel. Well I finally had a plug die and now bought some Odonnell Medium/Hot plugs but it lasted for less than a tank in my OS .30VG. Is it the wrong plug for my application? I know hot plugs are generally for smaller engines, and the .30 is kinda big, but the next coldest plug (medium) states 25-30% nitro, which is not what I'm running.. I did notice the filament is a little thin on these plugs. Should I be running a hot plug in my small blocks and a medium or cold in my big blocks? I don't need to squeeze every ounce of performance out of my engine, I just want it to be reliable/easy to tune and last long.
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Old 04-17-2010, 03:55 PM   #2
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I have a mixture of small and big block engines in my vehicles and and have always used whatever glow plug came with the engine. I also always run 20% nitro fuel. Well I finally had a plug die and now bought some Odonnell Medium/Hot plugs but it lasted for less than a tank in my OS .30VG. Is it the wrong plug for my application? I know hot plugs are generally for smaller engines, and the .30 is kinda big, but the next coldest plug (medium) states 25-30% nitro, which is not what I'm running.. I did notice the filament is a little thin on these plugs. Should I be running a hot plug in my small blocks and a medium or cold in my big blocks? I don't need to squeeze every ounce of performance out of my engine, I just want it to be reliable/easy to tune and last long.
I'm not expert, by any means, but, a general rule of thumb is for more nitro, you can run a cooler plug, but that's not an absolute. I generally run a P3 (super hot) in my OS Speed, but will switch out to a P4 (hot) when the temp gets up in the mid-high 90's. The hot plug will allow you to run your engine a bit richer without fouling. I run 30% race fuel all the time, whether I'm racing, or just goofing off.

I think your problem with that particular plug, is that the taper on the OD plugs seems to be just a bit different that OS. I had a similar problem with a 97T in my Speed, and when I switched back to OS plugs, no issues. I'd suggest getting a few P3's, and P4's, and see how they do for you.
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Old 04-17-2010, 03:58 PM   #3
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What is the taper? Both of my plugs are completely flat at the bottom (around the element).. I don't know if this is what you're referring to? Thanks for your reply!
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Old 04-17-2010, 04:06 PM   #4
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Originally Posted by norco kid View Post
What is the taper? Both of my plugs are completely flat at the bottom (around the element).. I don't know if this is what you're referring to? Thanks for your reply!
I think he is refering to the taper of the button head (were your glow plug screws into) The plug you replaced it with might not have been the right taper. Theres no like taper option when you buy glow plugs but they are all a little different. So, if you have an OS engine, stick with OS plugs, same with all other motors. You dont have to, but you know that will fit right that way.
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Old 04-17-2010, 05:09 PM   #5
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What is the taper? Both of my plugs are completely flat at the bottom (around the element).. I don't know if this is what you're referring to? Thanks for your reply!
Ah, then you do not have the Turbo style plugs....your's has a little copper washer too, right? That being the case, check out these two links.

http://www.osengines.com/accys/choosing-glowplugs.html

http://www.osengines.com/accys/glowplugs.html

There really is no "right" glow plug...it's like saying, what's the "right kind of shoes". There are so many variables to contend with, that the best plug for one part of the day, could be wrong several hours later. It's all about finding the best performance for YOUR application. Generally speaking, you should stick with a hotter plug if you're not running the engine at high RPM for extended periods (like an on-road car). You'll be able to run the engine a bit richer, will have less fouling, better idling, etc...

If you're engine uses a long plug, look at the OS LC3, or McCoy MC59. If it's a shorter plug, run the OS no. 6 or no. 7.

Honestly, your plug could have given up the ghost quickly because the engine tune was a little off. I've had an OS LC3 last 15 minutes before (I had my engine too lean....oops ). This was right after one that lasted almost a full gallon of fuel.
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Old 04-17-2010, 05:16 PM   #6
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an Odonnell standard plug is to long for an OS engine, OS standard plugs are shorter so if you tryed to run a standard Odonell plug in your OS engine it protruded to far into the combustion chamber and that is the reason it only lasted a tank of fuel. As a general rule OS plugs work best in OS engines. An OS A3 or OS #8 plug would be good for your .30 VG on 20% nitro. That being said; Odonnell does make glow plugs specifically for OS engines and the will always have the letters OS in the part number.
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Old 04-17-2010, 06:41 PM   #7
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an Odonnell standard plug is to long for an OS engine, OS standard plugs are shorter so if you tryed to run a standard Odonell plug in your OS engine it protruded to far into the combustion chamber and that is the reason it only lasted a tank of fuel. As a general rule OS plugs work best in OS engines. An OS A3 or OS #8 plug would be good for your .30 VG on 20% nitro. That being said; Odonnell does make glow plugs specifically for OS engines and the will always have the letters OS in the part number.
Well, there ya go......a person can learn something new every day. The only non-turbo plug engines I run all take a long plug, so I never knew the OD standard was longer than an OS. Having it stick too far down would certainly have created pre-detonation, which does indeed kill glow plugs.

I'll have to file this away for future reference.....
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Old 04-17-2010, 07:15 PM   #8
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Default OS #8

OS # 8 works the best with the 30vg.
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