Thermostat Troubles....every year

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

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

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.

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.

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 did pull one of the plugs and started the engine and revved it and water sprayed out.   According to Skidim that is supposed to be how to test if the circulation pump is working or not.

So I took the boat out today with the new raw water pump PCM Thermostat. Seemed to run fine for a while then it heated up suddenly again.   I pulled it and it cooled right down. Put it back in and it ran fine for a while right at temperature and then suddenly heated up again. I don't understand why it runs fine without it.   I took it home and tested it in water. It opens very wide at 190 and about 1/4" at 170 and not at all at 160.
Maybe I have bigger issues like a cracked head but I am at a total loss right now.   

tryathlete wrote: I would call and inquire what the "rebuild" includes. Ebay water pump

Cut and paste from ad,

PRODUCT DESCRIPTION: OEM Sherwood G20 / G21 Raw Water Sea Pump. Disassembled / Media Blasted / Inspected / New Parts Installed / Painted / Tested. New bearings, SS bolts, impeller, o-ring, gasket, mechanical seal and retaining rings are installed. Grooved wear plates are resurfaced or replaced. The pumps are painted Black and the body is left brass. They are tested and lubricated with glycerin impeller lube.

Me too!
I wonder if maybe it's getting hung up on the housing some how. Going to look at that. i know that they have changed the design of the Ford Thermostats in the last few years and you can't hardly find one like the original. Even the oem ones from PCM have a different design.

Not in brackish water. (Montana). I did see the rebuild on eBay. I Winterize by draining the engine. then sucking marine coolant through and then draining it again. Not sure if the coolant could be causing problems but again put a new stat in as part of the dewinterizing process.

Hollywood--one side removal. This was key! Starboard side came off easily.

Tryathlete: I was able to get mine out without removing the hoses.

I don't think the gauge or the sender on mine is wrong since the water was hot when I pulled out the thermostat plus I replaced the sending unit on mine last year before I figured out I had a bad thermostat at that time.

I am going to go ahead and order a new water pump. Pricey but I am a little suspect of it anyway and it has been making some noise lately. Will get the new stat and pump on with new impeller and see what happens. Might be overkill but I have some church camps I am committed to in early July and don't have a lot of time to be messing with things,

Not thread jacking hopefully--can I replace the T-stat without removing the hoses from the housing on my GT-40? Is there enough slack to lift the housing still attached to the hoses? Mine are stuck on and i just want to get the stat in since mine is stuck open.

Hollywood wrote: I would be testing the RWP performance

x2 What he said

It doesn't heat up at speed without the thermostat in.