When I built this engine I put a 180 thermostat in it and whenever I ran it while testing every thing it never got up to temperature. I'm using a aluminum 3 core radiator, flex a lite mechanical fan that pulls more air for a 4 core radiator and running aluminum heads. I switched to a 192 thermostat and it still only runs about 160 degrees. I took it for a ten mile drive yesterday to check out the heater I installed because I just installed the door windows and wanted to see how it worked. Outside temp was 47 degrees. Still not satisfied with temperature living here in the pacific northwest. Today went for another drive to warm it up and then when returned home I blocked off front of radiator with cardboard and let it idle for ten minutes and it finally got up to 183 at the gauge and thermostat housing, Outside temp was 37. I'm thinking maybe fan is drawing to much air, radiator to big. I would hope that 2 different thermostats were at fault.

 

If you've tried 2 different thermostats and you're still not coming up to temperature, I would question the accuracy of the gauge and check that before doing anything else drastic. I had a SW mechanical temp gauge that was bad, new right out of the box which I wouldn't have expected, chased my tail looking for a problem that didn't exist, and cost me an intake manifold in the process when the thermostat housing bolts broke. I don't take anything for granted anymore.

The whole point of a thermostat is to regulate and maintain a set operating temperature. If you have a 192 stat, the temp should be 192 at that point, which is where the water to the heater comes from, so your cabin should be plenty warm. Water will obviously be colder at the bottom of the rad and through the water pump, but by the time the water gets to the top of the engine, it should be hot again and regulated by the thermostat, no matter the size of the fan or rad. Ambient temp is well above freezing so you shouldn't need radiator blocking.

This is assuming also that the engine is running properly, you're not running too lean or too rich, your timing is correct, your combustion is efficient and your exhaust temp is good. These would be a few things to check, and perhaps your next purchase might be an infrared thermometer that can take temp readings at different places around the engine.
Here's an example...https://www.homedepot.com/p/Klein-To...-IR1/313516785

 

I used a infrared thermometer on the engine and temps seem consistent with gauge. Dakota Digital. I had other gauges hooked to the engine at first when I was breaking it in. Temps were the same. Timing is 12 degrees. I have Edelbrock top end kit in it. It seems to run fine. One time last summer it did get close to 180

 

 

You could always do the thermostat in a pan of water test, put in on the stove with a candy thermometer and check the opening temp.

 

You have a picture of passenger side hook ups of heater at pump and manifold? That fan without a shroud is just making noise and blowing air in the breeze so not a problem in your case. The thermostat as 52 Merc says shouldn't let hot water go to radiator until it starts to open. Is it a stock Ford WP or some high flow? Just curious.

 

It is a stock water pump

 

I had the same problem on my 302. But first it was running hot during 55 mph open road driving at 230 degrees. This was after after being over hauled and bored .040 over. I know that makes them run hotter. But it ran around 180 on the dyno. Before I installed the engine it I took the radiator (2 core) into a shop and had them boil it out and flow test it. They said it was good. But turns out that engine wasn't happy with it. After much troubleshooting I finally changed to a new 4 core bass copper unit, and then it ran too cool, at 155 degrees. I removed the fan from the water pump and installed an electric fan and a shroud which cut down on the air flow through the radiator and it ran right at 180 driving on open roads. For intown driving I added a thermostat to control the fan, it trips on at 195 and will bring it back to 180 and then shut off. Don't know if that is an idea or not, or even the right way to do this but it has worked well for me for around 10 years. But now days it's running a little warmer and the radiator is leaking so I need to decide to see if I can have it repaired, or buy another.

 

I was thinking about electric but was not sure of clearance. I have 4 1/4" between radiator and pump.

 

There should be little to no flow through your rad with the thermostat closed . Possibly too much flow through your heater core ? Try pinching a heater line .

 

Agree with Ebear, does your heater have a water flow control for cabin temperature control? Your heater core may be acting as an unregulated heat exchanger for your engine and cooling it down too much. The thermostat does not regulate that flow circuit. Pinching the hose shut is an easy way to test this, give it a try.

 

Any of the core replacements I've made on my newer vehicles I use a restrictor in the upper manifold hose connection. Not for cooling purposes but to keep from popping new cheaper built cores. 5/16 hole and still get plenty of heat. If the hose pinch doesn't work try a 192 from a Ford parts counter after you try the hot water thermometer in a pan test.

 

If there is no air flow over the heater core it will do minimal cooling. I would try blocking off (or restricting it at minimum) the by-pass hose at the thermostat. I see you have some type of late model or aftermarket thermostat housing which may be allowing a larger amount off water to by-pass the thermostat. It will not hurt you to block the by-pass, at least for testing purposes, and see if that brings your temp up closer to the thermostat temp.

 

I'm not sure I agree with the bypass theory . Would the bypass not just recirculate coolant in the engine providing no additional cooling ? If the temp gauge is accurate and the thermostat is working and installed correctly the only additional cooling would be via the heater core . I see that he has the heater hoses running into the fenderwell which would add a certain amount of cooling courtesy longer hoses and cooler environment .

 

Poker, if you get into the thermostat again, make sure you look at how the thermostat seals to the housing and intake manifold. I noticed by googling Ford thermostat housing and thermostats that some versions use rubber seals and others use paper gaskets. Some look like they have a rubber ring that captivates the thermostat then that is inserted into the machined pocket for the thermostat. Obviously a thermostat loose in the housing will leak coolant to the radiator even though it is closed. Hope this helps.