Would like your ideas about this. Ever since my 351M was rebuilt and converted to a 400 about 5 years ago, fairly stock, I have run the correct hat style thermostat. For awhile, I ran a 195 but didn't like the idea of all that heat and the fact that I kept having carb boiling issues (Holley 600 and an Edelbrock 2171 intake) at long idles in the summer heat. I switched to a 180. Have been using a Tim Meyer unit since he came out with them. I have an aftermarket temp gauge with the sensor in the thermostat housing and the factory gauge still hooked up normally. No driveability issues or overheating. Runs super, loves fuel.

Up until this past winter, summer or winter, the temp gauge always read a dead 180 once warmed up. It might have crept to 182 in summer heat at a traffic light. I have verified the accuracy with a laser gun on the housing. But, this winter, I was seeing temps only at about 170-175.I figured the thermostat might have lost some of its regulating ability. Since some say that a cold engine wears too quickly, I decided to install the original RT192 Ford thermostat I had been holding on to that I bought from E bay, a couple of weeks ago. But, it seemed to only raise my hot temp to about 190 or so. The factory gauge didn't even get to the mid point but it did read hotter than the 180.. We had an 80 degree day in Atlanta last weekend and after a long idle stop to chat with my brother, my carb boiling problem returned and when I went to take off it started bogging down until the hot fuel cleared out. Thought I was about to be stranded. I do run a 1/2" divided- down- the middle wooden spacer. Haven't had this problem in 4 years. Only resurfaced after changing to the hotter thermostat. I can't believe that 12 degrees made that much difference but it did. And I always use non-ethanol fuel.

So, I came to the conclusion I better go back to the 180. I decided to order a new 180 thermostat from Tim Meyer. Got it in 3 days. (Great service). I've become good at being able to change one out in 45 minutes with clean up and all and no leaks, I've done it so many times. Knock on wood. I went ahead and changed the oil too. Driving around this weekend with temps in the 70's, the gauge is reading like it did in the winter-about 177 or so as well as the temp gun on the housing. . Now the temp check on the heads is about 185 or a little higher right at the front under the intake. You don't feel any heat from under the engine area at all or near the grille. Seems like a good thing, but strange.

I have learned that my carb just doesn't like that extra 12 degrees heat from a 192 thermostat. I could tell it was not running as well as before with the 180, even before the bogging problem appeared. Now the 180 has it running great again. But, I am perplexed as to why a 180 thermostat, unless off on calibrations, is not even allowing the engine to run at 180. Shouldn't it at least run 185? It just seems something has changed that is making the whole system run a few degrees cooler than it ever had, no matter which thermostat is in it. If the thermostat opens at 180 and is supposed to regulate it there, I would think the actual engine temp would be a little hotter. Don't modern day cars run a little over what the thermostat is rated for?

It has a Murray standard radiator, factory shroud, stock fan blade, no clutch. I even have an overflow tank that works with a13lb radiator cap designed for the back and forth flow like on the 80's models.

I feel better with the 180 back in it. So many people have trouble with overheating issues they can't seem to get solved, but I have just the opposite. I'm only a few degrees cooler than I think it should be, but just seems funny. I will continue to change my oil using only Brad Penn 10w40 and a Mobil 1 filter every 1500 miles to try and avoid sludge build-up. Many guys would probably love to have this issue. Guess I'm not going to do anything further but still can't figure out what's changed since last summer. Both the aftermarket gauge and the factory gauge are reading slightly lower than they ever have. The factory gauge barely gets beyond the "L" at the low end. When the 192 was installed, it was getting to about the first line above the L. Surprisingly, the factory gauge seems accurate and does not vary like many folks experience.

Community thoughts? Should I just be satisfied there's nothing wrong? Who else is running a 180 and hat temps do y'all see?

 

All the temps you stated are well within the normal range. you're splitting hairs really.

All a lower temp thermostat does for a rig that over heats is buy you a little time before it overheats. it doesn't fix anything.

Around here 20 below isn't uncommon and zero is common so lots of people run winter fronts, or just cover half your radiator with cardboard between the radiator and core support. it helps the engine control it's temperature better . when it's cold you could try that.

 

The 351M in my 78 Bronco is cold blooded. During this winter/spring it'd only get to about 157. I had a bad fan clutch which had the fan running constantly. I replaced it with a new one and that helped. The PO had a 180 thermostat in the block. I replaced it with a 192. After all that I consistently got 180+ and about the highest I got was in the upper 180's. My heater still blows luke warm with a new core and all, which I don't like, but it is what it is. I'm swapping engines real soon though, so I stopped trying to improve my 351M's cooling system.