Heating, yep another.

[bobracing]

Just got the truck together and working bugs out.
On the way home the truck got a little hotter than I liked, the "L" in "normal" on a stock Ford gauge. So last night I took it for another drive to see why it was getting hot. Driving thru town and the DQ drive thru, the temp came up and sat at about the "O" where I think it should run. After a little town driving and fresh fuel the temp gauge staying about the same, we headed for the hwy. Out on the hwy I could tell how fast we were going by the temp gauge, "L" for 70mph and basically moved up and down as speed was changed. At 55mph the gauge would drop back down to about the "O-R" range and stay there. The gauge would also move up and down as we went up and down hills too but didn't affect it as much as speed.
After getting home I popped the hood and checked the fan to see if it was locked up, it turned fairly easily, but the truck was also back in the "o-r" range too. Did the same thing this morning, got to work popped the hood and again the fan turned easily, but again the truck was in the "o-r" range and the temp is about 30deg cooler this morning (95 last night vs 65 this morning).

Am I on the right track thinking the fan clutch is out? or is there another place I should be looking?

Thanks.

 

[OLDBULL8]

Sounds like everything is just fine to me. The fan clutch won't lockup until the air thru the radiator reaches 240 degrees, then it will roar like a hurricane wind. As long as it's in the NORMAL range you should be OK. You could always install a mechanical guage in the drivers side head at the rear pipe plug there. You could/should check the thermal spring on the clutch for dirt/oily, spray it with brake cleaner.

 

[PackRat239]

Sounds like thermostat to me. No thermostat means no temp regulation.

 

[franklin2]

Sounds like what mine was doing, and it was the fan clutch. I just bolted my fan solid and it quit doing it. You would think there would be enough airflow from going down the road at high speed to cool these trucks, but apparently there is not.

 

[bobracing]

I changed the clutch fan (and cleaned the new/used one), had a couple of extras floating around. It didn't really help so the thermostat is next.
Nobody in town seems to have a Motorcraft in stock, anyone happen to have the number handy?

 

[icanfixall]

Sure do and... Its easily found in the forum called... The Parts Bin..
Part number from motorcraft is E5TZ-8575-C
This is what the factory uses and it begins to open at 192 degrees and is fully open at 212 degrees. Never ever use anything but the factory original thremostat. Many have tried aftermarket and found out they plain just don't work the same. They generally fit ok but they can't pass enough coolant and they wont plug the block bypass when they open. When you remove the thermostat look into the block. You will see a machined hole. Thats the opening called the bypass. It closes off when the copper pill under the thermostat drops down when it opens.

 

[franklin2]

I changed the clutch fan (and cleaned the new/used one), had a couple of extras floating around. It didn't really help so the thermostat is next.
Nobody in town seems to have a Motorcraft in stock, anyone happen to have the number handy?

It's hard to find a good fan clutch. Most used ones are bad, most new ones you buy only last a few months, and the new ones are set to lock up after the engine gets very warm. It's a very common problem. That's why there is so much talk about electric fans, and it's also why I went to the trouble to bolt mine together.

 

[franklin2]

Also, the local radiator guy showed me a trick to check the radiator if you happen to have drained the coolant out;

1. Take the lower radiator hose off(or take the whole radiator out if you like)

2. Get water hose or a bucket of water and take the palm of your hand and block off the large lower outlet on the radiator(this may require another person to help).

3. Fill the radiator up full of water while sealing the lower outlet off with your hand.

4. After it's full quickly take you hand off the lower outlet. The water should come out full flow taking up the whole outlet volume. If it gurgles and struggles to drain, then your radiator is clogged.

 

[93cc7.3]

Mine was the same with a half open thermostat

 

[OLDBULL8]

This was a test done by someone else, not me, so I can't answer any questions about it.

The temperature measured below was from between the radiator and fan using a digital thermometer. RPM was measured with a optical tach. Ambient for both tests was ~67 F.

Ford-Eaton (22 years young):
Full engaged 180 F air with 1550 RPM @ pump and 1505 RPM @ fan
Full disengaged ~115 F air with 1600 RPM @ pump and 405 RPM @ fan
Note that disengagement temp was significantly lower then the newer model. It may actually have a slower reaction time and some delay.

4 Seasons 36963 (the $53 special)
Full engaged 177 F air with 1590 RPM @ pump and 1535 RPM @ fan
Full disengaged 145 F air with 1710 RPM @ pump and 415 RPM @ fan

The standard thermostat starts to open at 192 F and is fully open at 212 F. It seems to me that the air temp that activates the fan clutch varies with air flow, air temp entering the radiator, coolant temperature, and the heat transfer ability of the radiator. For example, if the radiator is corroded and clogged, the air would tend to stay cooler leaving the radiator even though the engine was hotter then normal.

Anyway, for the air leaving the radiator to get to ~180 F, the coolant itself has to be significantly hotter then 180 F. And, as airflow increases, the coolant temperature would have to increase to keep the air temp leaving the radiator at 180 F. 210+ coolant temperature before the clutch fully engages sounds plausible to me. The engineers probably wanted to stage the cooling so that the thermostat was pretty much full open before the fan clutch was full engaged for best fuel economy.

The fan clutch senses air temperature with a bi-metallic spiral element in the front. The outer end is fixed with some RTV in a slot, and the center rotates based on temperature. Re-fastening the outer end of the bi-metallic spiral would shift engagement temperature. The spiral straightens (un-winds) as it heats up, so that's the direction to move it for a lower temperature.