Thermostat Troubles....every year

So I read about the old style thermostat and the new style.   Nautique Parts and Ski dim sell a thermostat that looks like this.

From what I understand the original thermostats which you can still get at NAPA look like this.

The first one I ever took out of the boat looked like this too. NP assured me that the new style was an upgrade and would work fine. (It did for a season)
Went down to NAPA and got one.   Drove the one hour back to the lake and it seemed to work perfectly.   I ran the boat pretty hard for quite a while at different RMPs and the temperature was pretty stable. It ran a touch warmer on my gauge than the other ones did when they were working but I could watch it fluctuate on the gauge about 5 degrees when it opened and closed. To me the way the old style flows water through makes more sense. Somewhere on another thread I remember them talking about these different styles of thermostat. So after 2 trips to the lake today (180 miles) I think I solved the problem. Hopefully it wont show back up next weekend.

I don't agree with your original thermostat assessment. I have not pulled any of those out of PCM Fords. The PCM 454 has the bulky pass-through thermostat that sucks. It'd over $100 and does a ***************ty job of maintaining operating temperature. Their "fix" is a higher rated thermostat. Well that just doesn't seem right to me. Instead, we put a MerCruiser housing on the 454 and now use the normal looking, inexpensive 143 also commonly used in the Fords. Engine now runs right up to 160 and stays there, where before it would struggle to get to 120 idling, then climb to 170 and fall off immediately again with any amount of throttle.

The Ford PCM housing Gary showed has a natural pass through you don't need any funky thermostat.

I could be wrong on the old style new style. I just read it on this forum somewhere a while back. Could be bad information. I can just say that I have had 4 high flow thermostats in the boat. So far 2 of them this year.   The boat runs very cool with no thermostat in it and I believe the circulation pump is working based on the test shown on the Ski dim site.   The NAPA $8 thermostat is working for me. Wish I knew why.

Johnathan, did you ever get your temp issue figured out?

It would be interesting to boil both of them side by side & see which one opens 1st & by how much.