Thermostat parts

[18Warrior]

Hi. I have a 1988 5.7 Mercruiser, with an Alpha 1, Gen 1 outdrive. It has a standard cooling system, design 2. I went through the parts list, and ordered the following parts for it:
25-8M0204561 O ring
8M0109441 160 degree thermostat
23-8M0214947 thermostat sleeve
My problem is that none of the parts fit! They are all oversized by about 1/8-3/16" too big in diameter. Were there two different versions of the same thermostat housing made??
I've attached the parts breakdown shown here on Marine Engine.
Any help would be appreciated

 

[makomark]

Your engine serial number is ??

 

[18Warrior]

I don't have an engine serial number, all I have is the drive number. Which corresponds to the parts I looked up

 

[makomark]

The key to getting the correct parts is the engine serial number. The drive serial number realy won't help you narrow down the range of the engine choices, especially if its not the original drive.

That vintage engine, with standard (RWC) cooling should have a 140 deg t-stat.

My guess is that you looked up an engine that's newer than what you have.

There should be a serial number plate above and behind the starter, on the flywheel cover. If its tight getting to that area, a cell phone in camera mode may be helpful.

 

[18Warrior]

There is actually a serial number sticker on the port valve cover, but the number is gone. When I cool off a bit, I'll go have a look by the starter for a plate.