Engine gauge won't warm up

[Rearanger]

A constant fan can cool a radiator faster than the engine can generate heat.

I doubt with a thermostat maintaining constant temperature. At highway speeds you don't even need a fan. If what you say is possible then how would the engine get to operating temp in winter?

 

[Jason]

I doubt with a thermostat maintaining constant temperature. At highway speeds you don't even need a fan. If what you say is possible then how would the engine get to operating temp in winter?

Because the fan would not run constantly. The coolant is hot at the thermostat where it comes out, but is cooled through the radiator where it runs back to the engine. So the thermostat can stay wide open while the coolant in most of the engine isnt at 180 degrees.

 

[Earl43P]

It is common in the northern climates to block off part of the radiator in the winter.


Fan Clutch Mechanics
The fan clutch is driven by a belt or pulley directly from the engine's crankshaft. Inside the fan clutch are two metal plates and a special fluid. One plate is driven by the crankshaft, while the other drives the fan. The plates do not directly touch each other.

How It Controls Speed
The fluid inside the fan clutch thickens as it gets hotter. The plate attached to the engine is constantly spinning, causing the fluid to spin and turn the plate attached to the fan. When the fan clutch is cool, the thin fluid only pulls weakly on the plate attached to the fan, causing it to spin slowly and not use very much power. As the clutch heats up with the rest of the engine compartment, the fluid thickens. The thicker fluid acts like glue, pulling on the fan plate and making the fan spin almost as fast as the crankshaft. When the engine cools down again, the fluid thins and lets the fan slow down.

http://www.2carpros.com/articles/how-a-clutch-fan-works

http://news.carjunky.com/how_stuff_works/car_fan_clutch_what_is_it_c387.shtml

"The other potential symptom if the fan clutch fails is that it will draw the air at a very high rate, so in the cold weather the heating system will blow out lukewarm air and it won’t ever deliver enough sufficient hot air."

 

[Rearanger]

So the thermostat can stay wide open while the coolant in most of the engine isnt at 180 degrees.

Is the gauge sender close to the thermostat or at a point just after where the coolant enters the engine from the lower rad hose? Why would the thermostat stay open when the coolant around it is less than it's set closing temperature? At some point that cooled coolant, which is less than thermostat opening temp, will reach the thermostat and cause it to close. If what you are saying happens then no one's vehicle would warm up in winter at hwy speeds. I used to live in Alaska and never had a problem with any vehicle maintaining thermostat temperature. Yes, initial warm up would take longer, but once that was reached then the thermostat would maintain set temperature. I will concede that there is a point where a low enough ambient temperature will cool an engine faster than it heats, but where is the OP located, where the ambient temperature is so low that the engine loses heat faster than it is created through friction and combustion?

 

[Jason]

At constant highway speeds the engine is also under a constant, higher RPM load. However if the fan was also running continuously it would likely not maintain temperature.

 

[locovaca]

Is the gauge sender close to the thermostat or at a point just after where the coolant enters the engine from the lower rad hose? Why would the thermostat stay open when the coolant around it is less than it's set closing temperature? At some point that cooled coolant, which is less than thermostat opening temp, will reach the thermostat and cause it to close. If what you are saying happens then no one's vehicle would warm up in winter at hwy speeds. I used to live in Alaska and never had a problem with any vehicle maintaining thermostat temperature. Yes, initial warm up would take longer, but once that was reached then the thermostat would maintain set temperature. I will concede that there is a point where a low enough ambient temperature will cool an engine faster than it heats, but where is the OP located, where the ambient temperature is so low that the engine loses heat faster than it is created through friction and combustion?

Both the sender and computer sensor are before the thermostat in the lower intake so yes, even if the thermostat was constantly cycling because of a stuck fan clutch, you will see it on the temp gauge as a fluctuating needle.

 

[Rearanger]

However if the fan was also running continuously it would likely not maintain temperature.

But you don't even need a fan at hwy speeds because there is enough air flow to cool the rad, and I would suggest that the airflow due to hwy speed is more than the fan could supply. I also think that if what you say is true then you would see engine temp rise and fall. The OP also said he gets adequate heat from the heater, which would indicate the engine is at proper operating temperature. I think the OP needs to actually know what the coolant temp is at full operating temp and go from there, hence my suggestion to measure the upper rad hose heat.

 

[Jason]

I need diagrams to explain this I think.

 

[mephiska]

Wow, great discussion. Thanks guys!

So when I turn on the engine I do hear the constant vacuum noise, fan spins at full speed all the time.

With the engine off the fan does not spin freely by hand. I can move it but it's sticky.

Regardless of the fan clutch being the cause of my low temps, this fan clutch is most certainly bad, so I'm going to try replacing it. I assume I need the special tool on the 3.0 engine?

 

[Earl43P]

Looking at the 93 EVTM, the gage sender should read (unplugged) 74 ohms when the needle points at the Cold Mark. It should read 9.7 ohms when at the the Hot mark.

Another sanity check would be to test the ECT (two wire temp sender for the computer) http://www.fordfuelinjection.com/?p=28

If you find these two signals BOTH point to low coolant temperature, that confirms the diagnosis of a bad fan clutch. FWIW, the fan clutch WILL allow sluggish rotation of the fan (engine off and cold). What I mean by sluggish is, the fan will turn by hand, but will not spin freely. You can feel the viscous coupling.

If you feel ratcheting or a "catch", the clutch is bad.

The 3.0 fan nut (the big one) is reverse thread so Righty-loosey. .

Here's a link showing the special tool in use: http://stuffforyourranger.com/How_To_Installs/30underdrive.html