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1977 F250 460 heating problems

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#1 Old Ford Guy

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Posted 22 July 2016 - 07:40 AM

Hello Ford Truck experts. Sorry for the long winded text. I have a 1977 F250 Ranger 2wd, 460,C6, P/S, P/B, A/C, 3:73 differential, 4 row desert cooler radiator, 160 degree thermostat, 7 blade fan w/ thermo clutch, motorcraft 4300 carburator. Live near denver in Colorado.  I have had this truck since 1991. I rebuilt the engine soon after I got it. Found a builder out of a 1973 Lincoln with the early style intake manifold, good heads etc. Truck has always ran great, a real powerhouse and pulls what ever I want to. I used to pull a 18' ski boat and jet skis to Lake Powell in August just about ever year in over 100 degree heat A/C on without a problem. I started having heating troubles a few years ago. The radiator had a spot on the top tank that started seeping so I took it to a shop and had it and gone through. At about 110k miles, still having intermittent heat problems. The truck would just run a little hot, usually pulling a load and vapor lock, it has never boiled or steamed on me. After the vapor lock issue having quit on me a dozen times or so I replaced the water pump with a high volume Mildone pump, installed high volume 160 degree thermostat, new thermostatic fan clutch. I insulated the fuel line from the pump to carburator, I even got a very accurate dial thermometer and threaded it into one of the fittings directly on the top of the thermostat housing so I could monitor it. I tested the coolent for carbon monoxide before and current show negative. This January I decided I was done messing around and pulled the engine. All of the pistons were scored from the excessive heat so I just had it completely rebuilt by a trusted engine builder. I get it put back together and it runs perfect except it still wants to run hot, regardless of air temp. At 70 degree evening air temp it will run in the 185 to 190 range. At 90 degrees the other day it tried to vapor lock on me but didn't quite do it, it was running at 205 degrees.  My hose hydrant will run 20 gpm. When I had the radiator out, I just stuck the hose in the top opening just to see and it flowed completely at 20 gpm out the bottom, never backwashing out the top one bit? With the high flow water pump and thermostat I could see a significant increase in flow across the radiator. I thought it might be flowing too fast to cool, so I put an original style 160 degree thermostat back in it. I have been a auto mechanic for most of my adult life and worked most every kind of early Ford there is. Love the truck and have had it so long, you just know how it runs and when it's off. This has me utterly bewildered. My next step will be look at the Radiator again, this doesn't seem like it can be the issue. If anyone has dealt with a similar problem or thinks I missed something I could sure use some help.


Thanks for reading.


#2 miesk5


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Posted 22 July 2016 - 10:54 AM

Yo Larry,
I have all my Ford repair manuals, magazine articles, etc. packed away so I'll go by memory.
This *** indicates my best thought
Radiator Removed
*** CAUTION: Radiator internal pressure must not exceed 138 kPa (20 psi). Damage may result. ***

Back-flush radiator (8005). Position a high-pressure water hose in lower radiator hose location and back-flush.
Remove water hose connection and water thermostat as outlined.
Back-flush engine. Position high-pressure hose into engine through water thermostat and back-flush engine.

***Retarded timing causes overheating. DOES IT HAVE A fan shroud? on the fan. The blades should protrude about half way into the shroud.***

***Check for proper cooling fan clutch operation. Perform Fan Clutch Test. Refer to Component Tests in this section.
Did cooling fan clutch operate OK?***
I don't have the 7 blade fan w/ thermo clutch specs to test, so maybe you can look them up?
Tools needed:
Strobe Light
throttle adjusting tool
Start the engine and run it at approximately 1500 rpm until engine temperature has normalized.

Adjust the engine to the testing speed in the Specificationsat the end of this section.

Operate the strobe light at water pump test speed and aim it at the water pump pulley. Adjust the engine speed until the light flashes and the water pump pulley marks are synchronized.

Aim the timing light at the fan retaining bolts. Adjust the strobe light until it is synchronized with the marked fan retaining bolt (fan appears to stand still).

The fan speed must not be greater than the specified fan test speed at water pump test speed.

Turn the engine OFF.

If the fan speed was greater than the specified fan test speed, check for proper parts usage.

If the correct parts are used, replace the fan clutch (8A616).

If the part(s) are not the correct ones, replace the part(s) and perform the test again.

If the engaged fan clutch requirement test is going to be performed, do not remove the tachometer, strobe light or throttle adjusting tool.

If a Maximum Speed Fan Clutch Requirement test is not going to be performed, remove the tachometer, strobe light and throttle adjusting tool.

Maximum Speed Fan Clutch Requirement Test


If the disengaged fan clutch requirement test was not performed, follow Steps 1 through 5 under Minimum Speed Fan Clutch Requirement test.

Block off areas on each side of the radiator in the engine compartment and the front of the radiator grille, this will raise the temperature of the air striking the fan clutch and should cause the fan blade to operate at maximum speed.

Place the air conditioning selector, if so equipped, in the maximum position and the blower switch in the high position.

Adjust the strobe light to water pump test speed.

Start the engine and adjust it until the water pump pulley is synchronized with the strobe light. This will be near the engine testing speed given in Specifications.

Synchronize the timing light with the fan to fan clutch retaining bolt.

The fan speed must meet or exceed the specified minimum fan blade test speed at water pump test speed.

If the fan speed was less than the specified fan test speed, replace the fan clutch.

Will think about this and come back Saturday.
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