http://http://www.offshoreonly.com/forums/attachments/general-q/530207d1412193548-hp500-oil-temp-oil-temp-sender-location1.jpg

There are two ports on my hp500 oil filter/thermostat housing that are not used for oil lines. One is on the top (large port) and one is on the side (small port). Which of these should be used for a temp guage, or, which is after the cooler and which is before? Thanks in advance.

I have mine set up the same way you do. before hooking everything up I spent some time figuring out how the oil is routed through the cube by shining light through it. I'm assuming you know what hoses go where, the hard part is what the other holes are for. There are 4 holes under the filter,
1. center hole is oil return from filter to engine.
2. off-center hole number 1 brings the oil into the filter either from engine or from cooler.
3. off-center hole number 1 is where the oil flows to where we have our temp senders mounted.
4. bypass valve, i blocked mine.

The number 3 hole from my description will see what ever temp is flowing through the filter. Thermo closed oil flows straight from engine to filter. Once the thermo starts to open oil then flows to cooler first then back to filter then engine.

The large port that we aren't using I remember ruling that one out completely for temp sender but don't remember exactly why at this point. IIRC that port will see the oil before it flows to the cooler (notice it's inline with the hose to the cooler) but it won't see any oil until the thermo starts to open. I think that's why I ruled it out but I might by trying that port next due to not having any oil temp readings with my current location. Hope this helped.

I have my temp sender in the large port (picture is just off google) and the oil temp reads higher than I would like for oil going back to the engine. If this is before the cooler then I'm not worried about the temperature as the oil going into the engine will certainly be cooler. I may move it just to see what the temp is after the cooler.

I just moved mine to the larg port. my temp barely saw 190 last week in the small one. I want to see what's coming out of the engine as I know my oil coolers are working as they should. If I had the room I would install both but don't think it's necessary now to add extra gauge pods.