Need help identifying weird oil plug

[pnutbutterking]

Hi everyone, first time posting. I have a 2006 Four Winns 190 Horizon with Volvo Penta 4.3gl. I've been noticing some oil in the engine well and have been worried it was a head gasket. After a very detailed inspection including passing compression tests, etc, I found where it is coming from ... a very small 5/16 ID hole on the left side (facing aft) of the engine, in line with the starter, along the edge of the oil pan to block connection and it spits little drops of oil out while running. I've been to the local marine mechanics and they say it's an alternate location for a dipstick and you can buy a plug anywhere but I've ordered a few on Amazon and elsewhere and they just don't fit (which is what led me to finally use callipers to measure it at 5/16"). Anyone on here hear of this part before? I've picked up some 8mm rubber stoppers and also silicone but that's not a long term solution. Anyone on here hear of this part before? Photo attached.

 

[alldodge]

Pretty sure a dowel pin is used to seal it. Might even be laying in the bilge, or it fell thru and its in the pan

Merc part number 17-35465 and might be able to find it at a local auto parts shop
https://www.hardin-marine.com/p-50036-pin-dowel-2-mercruiser-17-35465.aspx

 

[racerone]

Did some starters use a support bracket ?----Bolt hole for that bracket ?

 

[pnutbutterking]

Did some starters use a support bracket ?----Bolt hole for that bracket ?

I thought about that but it's not a threaded hole

 

[pnutbutterking]

Pretty sure a dowel pin is used to seal it. Might even be laying in the bilge, or it fell thru and its in the pan

Merc part number 17-35465 and might be able to find it at a local auto parts shop
https://www.hardin-marine.com/p-50036-pin-dowel-2-mercruiser-17-35465.aspx

Dowel pin...I'll investigate that, thanks!

 

[racerone]

But the block may have been ready to have that hole threaded for certain models ?

 

[pnutbutterking]

But the block may have been ready to have that hole threaded for certain models ?

Maybe. My local Volvo marine mechanic looked at my picture and said it's an alternate oil dipstick holes and uses a simple rubber style plug you can get at any auto parts store but I've tried them all and they are too large. I've also looked at all of the Volvo Marine engine manuals and could not find it described anywhere.

 

[cobalt1999]

Google
"oil dipstick tube block off plug"

 

[Scott Danforth]

5/16" bolt and some permatex #1. call it done