I have an older Merc oil thermostat that I was told came off a HP500. Its looks like a 4" square block of black anodized aluminum with a yellow sticker that says "caution Hot"

Can anyone tell me what ports on this thing get piped to where ????

On the HP500 they got piped directly to the oil cooler. There are just two hoses that come off of it..you can see it in this picture along with the brass looking connections to the left of the "caution hot"...there is also a black sending unit and below that is the tstat..the big brass plug in the top I am told is for some sort of adjusting...

Here's a picture:
http://www.mercruiserparts.com/Show_...ER+AND+ADAPTOR

20 and 21 go to adapter on the block, 18 and 19
go to the cooler.

and it does matter which of the hoses connect to which
end of the cooler for proper oil cooling.

I can't remember as of right now, but I'm working on a boat tonight
with that system, I'll report back which end goes to where.

If you are looking for the block adapter, hoses and fittings, I have them. All Mercury factory parts.
PM if interested.

Thanks, That what I was looking for. But lines 18 &19 , Do you know what is the feed and what is the return????

When You are running the lines to the oil cooler you want the oil to flow the opposit direction that the water flows through the cooler.

here are a couple more pictures for you...

Bajapreds pics above show the correct routing.

Thanks , Thats what I needed

Bringing this back,up
need some help plumbing these and best filter to use
links no longer work

I am trying to plumb one of these as we type, I would also like to see the diagrams as well. Any help is welcome, TYIA