Missing Oil Pressure Sender?

I have a Mercruiser 260 (Chevy 350) in a 1979 Mark Twain 24 footer that I recently got. The boat has not been started in 2 years but I was told it was running very well back then (the owner got ill and eventually died).

So I am getting ready to restart it and I noticed an open 1/8NPT port on the port side of the engine, back near the oil filter (under the #7 spark plug). If I remember back to my hot rod car days, that is where the oil pressure sender should be. Does anyone out there know if I am right or if there is another explanation? To make matters more confusing, I didn't find a wire that should go to a sender if it was missing. Thanks very much!

 

No, I don't know.
Remove the spark-plugs, shoot some oil in and turn it over.
You'll know pretty quick if anything is missing as oil will come shooting out the alleged oil sender hole.

 

Thanks for the reply. That is about what I was planning, except I think I will save the mess and run a hose into a jug - just in case!

 

Are there any other parts missing from the engine?
It is rather odd for the sending unit to be absent, but you see no wire for it either.
When I said remove the s-plugs, I meant leave them out while you turn it over.

 

Thanks for your interest. No other parts are missing. Last night I got in there with a 1/8"npt nipple to attach a hose as I mentioned. The hole was slightly bigger, but not a 1/4"npt. Weird! It is right under the dip stick tube, so I am sure it is in the oil line

 

Will it take a thin wire probe or is it solid inside, like a blank.
Just turn it over two or three times as nothing "should" come out...
I'm not a V-8 guy so can't really help much there.

 

I don't believe that is a oil pressure port. Most 350 chevy's have a sender by the distributor 1/8 inch pipe thread and also one at the front above the timing cover that normally has a 1/8 pipe plug in it . I believe that threaded hole is 5/16 or 3/8 and was for a threaded ball, that a clutch pivot assembly was slid on and that had the other end pivoting on the frame. A rod came from the clutch petal to this assembly and another rod went to the arm for the clutch release bearing. steve

 

Hmmm... I think you are right. That is about where the Z bar for the clutch would screw into a small block chevy. I guess I will know for sure when I crank it over! Thanks for being so thinkative!

 

Where do the pull the oil from if they run the oil through an oil cooler on the boat?

 

Good point: Did you find an oil pressure sensor somewhere else on the engine?
There's not going to be two...

 

I plan on looking this weekend. The more I think about it, the more I don't think it is an oil port (even though it is right there). The engine block underneath is oil free and the bilge shows no sign of being oil soaked. Thanks again.

 

There actually can be 2, one for a gauge, and a 2nd for a warning buzzer.

 

Thanks, I will check that
I got a free boat with the same motor and out drive. Haven't even done anything to the Mark Twain as I want to strip the parts off the old boat and get it to the land fill