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What's this hole for???


Well-known member
Jan 26, 2001
Asheville, NC
1973 converted to 1980 custom convertible
There is a threaded hole just above the oil filter that is unplugged. My oil pressure sender it mounted on top of the block at the rear just in front of the distributor. Is this hole above the oil filter another location for the oil pressure sender? I have read of others who have the sender located close to the oil filter. I'm trying to find a location for my oil temp sender.


The hole just above the oil filter is where my sending unit is mounted. If yours is elsewhere that hole must be plugged with something.
Thanks for the confirmation. I thought that is what its for. Can't believe the hole was unplugged. I hope that explains some of the oil leak in the area. Now I can mount my oil temp sensor there.


Let me see if I get this

The hole was unplugged ( no cap no nothing?) when you found it..
and oil was not POURING out of that hole?

( people....... always trying to take my ice cream bar...... I've had it since I was a child)
Thats correct. Very little if any oil has been leaking there. In fact, the block in that area is a little dirty but not what you would expect. I never actually detected a leak from that area before. Go figure! Anyway, it will be plugged with a sensor now.


But if there's no oil flow.....

You will just be measuring block temp....

Still confused

Unless that port is plugged inside, it is suppose to be used to measure either oil pressure or oil temp. I already have an oil pressure sending unit at the top of the block next to the distributor, so I plan to install the temp sending unit at this location next to the filter. I have an oil temp gauge in my instrument cluster. The question I have to solve is why no oil was leaking out of this port without a plug. Could just be clogged with debris of some sort but not sure. Thus the mystery continues.


At Oil pressure of 35-70psi

and oil temp of 200+ degrees

It's gotta be a BIG piece of junk in there to plug it.

Somebody ( Like 69 my way) has got to chime in on this who's got a block..that's maybe in his garage loose.. that he could look at and give us his .02.

my 82 has a sending unit above the oil filter what its for I don't know, it also has the oil pressure sending unit by the distributor, the car does have a oil temp gauge in it to
I would check up inside the hole to make sure that it is indeed not plugged. I have a hard time believing that there is a big enough piece of debris in there to plug the hole against 50 or 60 lb. of pressure. I assume that this is a 1/8" NPT threaded hole (standard). Someone may have put a hex pipe plug into the hole. These will often screw in far enough before tightening that they will not be visible from the outside . . . . especially in an non-accessible place like this. The hex drive should be 3/16". Take a 3/16" allen wrench and stick in there to see if there is a plug buried in there a ways.


I've got an 81 and from your description the hole should be your oil temp sender. Funny that oil is not shooting out, I kind of thought you'd have oil everywhere without the temp sender in there. Go get yourself a small dental mirror that swivels, a good shop light and see if there's anything blocking the hole.
OK, I am assuming that the engine is in the car and visibility to this hole is not great. In my mind, there is no way debris could hold up under standard pressures. Take an allen wrench and insert it into the hole. My guess is that it has an allen head block off cap in it. Get a few and try them in the hole and see if one feels like it is gripping a female allen plug. Now backing it out may be a whole different story and it should drain any oil that is still in the block. I have never had good luck getting these out, especially from an older engine. Good luck. Just my two cents (not normally worth more than about a cent and a half).
Update for the curious:

I got a small automotive swivel mirror today, so I hope to begin the search for the mysterious plug soon. I was watching Scooby Doo with my kids and figure if they can solve the mystery of the "Creeper" then I can solve this mystery.


On most Chevy blocks there is a tiny hole inside the treaded hole.
Kinda like a pin prick on a water balloon.
How much oil would you go through?
"On most Chevy blocks there is a tiny hole inside the treaded hole. Kinda like a pin prick on a water balloon. How much oil would you through?"

I don't really have to add any oil between oil changes; however, I only drive the car about 1,500 miles per year. I change the oil long before I hit the 3,000 mile mark per change.


Your ride, stick or auto?

1973 block??

So the Big hole ( which I think) everybody's talking about is for the pivot for the clutch linkage between the block & the frame.

I'm digging to see ( somewhere ) I have the oil flow X ray internal to a small block.

More to come,
Holy oil cooler

So there is a line on the side of the block on top of the oil filter casting on the block (center line).

It shows a plug of some sort that is used for sending the filtered oil out to a cooler, where the return is..dunno.

It shows that it is threaded.
But I cannot find any other reference to it.

There should be a pipe plug ( female square hole) in the raised part of the casting.

This is a different hole than the clutch linkage support.

Still lookin,


I applaud your determination on this. I also found out today about the other hole being for the clutch linkage. According to my source, the other hole should have a pipe plug of some sort. I'm going to use my new chinese made swivel mirror to look up in there for a plug.


Love a good mystery

If I don't know, I dig & do research and learn more.

Keeps the mind...ahhhhhhhhhhh
keeps the mind..er um I had it right there a min ago.

Uh Hello ....focus

Sharp yeah that's it


hole above the oil filter

I was asking my father in law the exact same question tonight believe it or not. My car body is off right now so we were able to look into the hole. The hole goes into the block but not into the oil chamber. It comes out next to the flyweel. Therefore it could not have leaked oil. I dont know what it is for. The linkage on a manual was my guess as was posted earlier( my car has an automatic).
The question that I have is on the hole to the left of the one you are questioning. Same size same threads.

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