Wow! That engine block coolant drain plug was tight!

   / Wow! That engine block coolant drain plug was tight! #1  

SmallChange

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Tractor
New Holland WM25 with 200LC front end loader, filled R4 tires 43X16.00-20 and 25X8.50-14 (had a Kubota B6200D with dozer and R1 tires)
Just finished my first coolant change on this tractor, which I bought new. This included removing the drain plug from the engine block.

Wow! It sure was tight! There's an assembly kind of in the way so I had to use a universal joint on the 14 mm socket. First I tried my 1/4" ratchet drive, which fit into the space with as little angle as possible, but couldn't get enough torque. So I went to 3/8" drive ratchet. Couldn't get enough torque on that either. So I went to my 1/2" drive using a breaker bar that's probably 18" long, and even that I couldn't get enough torque at first. I had to squeeze into a better position to do it. I'm going to estimate about 50 foot pounds it took to loosen it. Then it was perfectly easy. The threads looked to me about like a 1/4" NPT, but I'm just eyeballing it to describe it, and I suppose it was probably a metric thread that I just can't recognize by sight.

The plug was clean, with no thread sealant as far as I could tell. Hole was clean too, as well as I could see it. When I put the plug back in, I used PTFE tape on it, and probably got less than 20 foot pounds torque, which still seemed like a lot for something pretty small that I'd hate to strip. I think PTFE tape makes the torque to install today, and the torque to remove in a couple years, more similar. That is, it helps prevent getting the thing stuck.

Why so tight? And why don't they put any sealant on it (or at least nothing I could see)?
 
   / Wow! That engine block coolant drain plug was tight! #2  
Was there any sealing shoulder or washer under the head on the plug?

Curious if possibly BSPP or metric that have some form of seal vs sealing on the threads. These typically turn easy once broke loose.
 
   / Wow! That engine block coolant drain plug was tight!
  • Thread Starter
#3  
Was there any sealing shoulder or washer under the head on the plug?
Nope. The plug had maybe 1/4" of threads still outside the block. I noticed maybe 4 or 5 threads were actually spray painted like the block. The hole penetrated right into a rough cast surface of the block, no boss or spot facing or counterbore at all. The bottom of the hole seemed to open out into a larger space, and the bottom of the plug was a bit crusty and wasn't a machined surface; it looked a bit unevenly concave as if perhaps the threads were rolled (but I'm guessing as to the reason).

The oil plug in the pan threads into a boss and has some kind of gasket under its fairly large head -- maybe an O ring, if I'm remembering right. So I know what you mean. But this just looked like a pipe plug.

And by the way, this plug was hard to break loose, but it turned easily once it did. I probably rotated it 30 degrees and realized it wasn't resisting at all, and spun it out with my fingers from then on. It also got looser, rattling loose, once it made 2 or 3 turns, like a pipe taper would.
 
 
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