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D 21 spark plug size 14 mm 18 mm?

MARMON77

Well-known member
Ordering a CHT gauge and sender but can't order the sender because they need to know the size in mm that the plugs are either 14 mm or 18 mm. I've called several parts stores with no luck at all. Anyone have an idea or know exactly?
 
my 220 runs in the 180 oil temp. just build a shroud hope to drop that, not sure about the chts sure would like to know some for research :lol: :roll:
 
I think around 450 for A/C. For some reason that sticks in my head right now. I am not sure though if 450 is normal or high.
 
Thanks Grant will be ordering it tomorrow! I've heard / read not to run over 400 but not exactly sure.
 
Cylinder temp should be below 400 degrees F for long life. In airboats that is hard to keep. I have seen it run as high as 500 when running slow & high RPMS.
 
You need to check the engine manufacturer to see the maximum temp allowed for their cylinder. Most aircraft engines list something over 500 and usually 550 as maximum. However, for long life it is best to keep it below 400 if you can. I size my oil cooler to keep the temps down to 400 at cruise and I never let it get over 450. I'll slow down or shut down if I see the temps get close to 450. I usually get max oil temp at 170 also but I have seen as much as 190.

A large oil cooler doesn't do it all. I had a huge oil cooler on one engine that never got over 140 and I could still get high cylinder head temps if I pushed it too hard. Do what it takes to keep the temps below 450 and you'll run for a long time.
 
MARMON77":2k5aa7sp said:
Ordering a CHT gauge and sender but can't order the sender because they need to know the size in mm that the plugs are either 14 mm or 18 mm. I've called several parts stores with no luck at all. Anyone have an idea or know exactly?

I have a new to me boat that I haven't had out yet--- it doesn't have a CHT guage but I probably should get one-- any recommendations on which one and where to get it and price ?
 
Aircraft Spruce has them for a litle over $50 and about $12 for the spark plug type sensor. If you can keep your cylinder temps below 450 you will keep that engine running for a long time. Without a CHT gauge you have no idea how hot the cylinders are getting. Even with low oil temps you could still burn up a cylinder. I only monitor one cylinder.
 
Hey JoeH, Just ordered mine from Aircraft Spruce. The gauge is a Micro 1000 $52.95 and the sensor for mine was an 18mm one $14.95. Coming out of Cali. will be here Mon.
 
Thanks -- I'll check out the Aircraft Spruce site as long as I have to do some work/wiring. I might as well do it now
 
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