What is this? PLEASE

[Lcw3168]

I have a 1998 4.3 L Mercruiser Thunderbolt on the port side to the left of the Lower Blue drain hole is a round circle that's brown with a bolt in the middle can someone please tell me what that round brown circle is.

 

[Bondo]

Ayuh,..... Welcome Aboard,...... A picture is worth a thousand words, 'n yer comin' up short on both ends,....

Yer description isn't ringing any bells for me,....

 

[dubs283]

can someone please tell me what that round brown circle is.

First WAG I have is nothing related to boats, at least in a pragmatic sense

Post a picture of the area/bolt circle in question. It'll help

 

[Bt Doctur]

If installed with a bolt it could be the knock sensor

 

[ScottinAZ]

First WAG I have is nothing related to boats, at least in a pragmatic sense

Post a picture of the area/bolt circle in question. It'll help

yep, first thing that pops into my head is an expandable rubber freeze plug..... without pics its impossible to know, and with pics, it would be impossible to ignore......

 

[todhunter]

yep, first thing that pops into my head is an expandable rubber freeze plug..... without pics its impossible to know, and with pics, it would be impossible to ignore......

I was thinking the same thing. Someone froze the block and pushed out a freeze plug, then slapped a bandaid on it.

 

[ScottinAZ]

I was thinking the same thing. Someone froze the block and pushed out a freeze plug, then slapped a bandaid on it.

granted, its on a V-6, I wouldnt want to try and fight putting one in "properly" on a boat either.... enough of a PITA in a vehicle with some actual clearance...... with a boat, its damn near engine out type work