[dsinger]

Using the serial number on the motor it tells me it is a 1991 Mariner Magnum 111 2.5lt 150hp. I ordered some head gaskets and they did not fit. I think the powerhead was swapped out on this thing. If I us Mercury's Website I can search the old head gasket part number and located it but it will not give me a year range. The head gasket part number is 27-41244T02. How can I figure out the year of the power head. The serial number on the power head is 105822113. I looks like the letter C might be in front of the mumber but it is hard to tell.

[Chris1956]

Compare the number on the freeze plug of the powerhead(top port or starboard cylinder bank) with the serial number on the transom clamp. If they are different, you may have a different powerhead.

[dsinger]

It is gone.

[Chris1956]

the "Serial Number on the powerhead" you cited has too many digits to be the motor serial number. It should be 6 digits following a letter like 0CXXXXXX, or 7 digits.