Hey everyone,

Ever since my X had a COP fail I've noticed that my engine has been running cooler than usual. It always used to stay between 180-187°, but in recent weeks it's been staying about 10 degrees cooler than that, and sometimes dipping into the 160's when coasting down a hill. Time for a thermostat swap!

This is about the easiest repair that can be done, and if you can change a tire this is well within your capability.

MODERATORS NOTE:

This is a sister thread to Tom's thermo "How To" found here: https://www.ford-trucks.com/forums/1...l#post12907913

The ensuing discussion (of which the posts have been transplanted to this thread) detracted from the overall purpose of the "How To" thread, so I cut it and made the discussion aspect its own thread.

 

That little hole is just for any air trapped in there. Is the old one a different length? How do you know how cool it is? Is it hotter now? The thermostat doesn't control the heat but only when it opens. Do you know what the bottom valve does? If not I can send some info on it (if I can find it again).

 

You can't see in the pic, but they are both stamped 185°. Which means that it opens at 185° to regulate the engine temperature around there. Heat generation is controlled by the right foot!

ON edit: thanks for the info about the hole, perhaps that's why I didn't have to burp any air out of the system? This is the first vehicle I've ever had that I was able to just fill up and drive away after draining the radiator and the block.

 

So why did you change thermostats? Why is one longer? Do you know what the bottom valve is for? How do you know it ran cooler?

Yes you should always burp the system, it is done at that pipe that sticks up out of the front of the intake manifold in the pass side.

 

Because it was running cooler; instead of the usual 185-190° it started running between 165-175°.

No clue, I presume design changes. I assume the bottom of the valve is the heat motor that operates the t-stat, but I never read any detailed explanation.

With my ScanGauge. Photo can be found HERE.

Didn't know that, but I had no issues without doing it either. I'll keep that in mind for next time.

 

Stat temp has nothing to do with engine running temp.

It's very important that they are the right length, are they both MtrCrft?

You don't always need to burp it but that is how you do it. The bottom part allows the engine to circulate water so it is efficient, eliminates localized hot spots, and warms up quicker. I will send diagrams of how it works later today. When that bottom valve closes all the water comes from the radiator and it quits circulating in the engine.

 

I'm not sure what you're getting at here, but the thermostat exists to regulate the temperature of the cooling system.

Yes, they are both Motorcraft. Of course one is 13 years older than the other.

 

Read this;
ARE Cooling

It's not like the old days with one valve. An aftermarket stat is hit or miss so it is worth it here to get a Mtrcrft stat for a couple more dollars. Were those 2 stats different lengths or was it just the picture?

 

huh?
It sure does. After it opens it's constantly adjusting to what your engine is generating in heat output. Going a steady 65mph on flat ground in cooler weather it's hardly open to the radiator and most is recirculating.
Drive up a steep hill in 115 F and floor it and it will be wide open to the radiator and there will hardly be any recirculating.

 

As I said before, they were both Motorcraft thermostats. And it's not just the picture, they aren't the same length.

 

That might be why they don't function the same. I had one that only had 1/8" clearance at the bottom valve which affected my warm up time.

 

Yes it does.

The thermo isn't just opened or closed.

Exactly.

There are at least three different degree rated thermo's available for the 7.3L PSD.

• Stock thermo
• Terminator Engineerings 180* thermo
• Diesel Site's 203* thermo

Joey at Terminator came up with the 180* thermostat to help rigs that run his duel HPOP system keep the engine temps (and the oil) cooler than provided by the stock thermo.

Bob at Diesel Site is a proponent of higher engine temps to help with a supposed better combustion event, so he came out with the 203* thermo that is found on the International 7.3L engines.

All three produce different engine oil operating temps.

Stewart

 

I'm just saying it can't get below 185* after it first opens so it doesn't regulate anything above that which is where it normally runs. It's all radiator etc after that.

 

Not sure what you mean, but it sure does regulate.
It has a range of opening. Not sure where the numbers are but I think it STARTS opening at 185 and is probably fully opened by 195.
So at 190 it's probably half way opened.

Don't take me for granted on those numbers but that's how it works.
It is NOT just an open/closed valve. It has many positions it can sit in.

 

I agree with you on most things Brent, but you're dead wrong about this. The thermostat is constantly adjusting rates of flow to maintain a set temperature. The flow through the radiator is always just enough to maintain the set temperature.