1996 f-150 Special with factory cooling for towing, 5.8 L

1.Truck ran perfect temp, no variation..
2. Water pump was starting to drip
3. replaced water pump
4. Ongoing temp would rise to center of dsh temp gauge then jump to right white line, but not into red.
5. Then would bonce between normal and hot.
6. Part exchange started.....New thermostat, radiator cap, fan clutch.
7. Same erratic behavior. for 1000 mils now.
8 No oil in the coolant. No coolant in the tail pipe.
9. It does push coolant into the overflow tank

Here is the kicker

10. It runs cooler if I drop transmission down to 2nd and run at higher RPMs, The temp drop is immediate.
11. It seems this added water flow/pressure pushes thru something, or pushes cooled water thru engine
12. Perhaps a partially clogged radiator?

Any insight would be much appreciated

 

I think you need to confirm your temp gauge is reading correctly before you go any further.

 

If all that started right when you replaced the water pump I would be inclined to replace the water pump again with one of a different brand. The impeller on the water pump may be slipping or otherwise somehow not pumping adequately.

 

Could possibly be a water pump that is for V-belt drive and so it rotates the wrong way?

 

Is the needle bouncing as in its snapping to one side to the other or is it "swaying" from the extremes? if its snapping its probably the electrical connection to your engines gauge temp sensor(different from the computers temp sensor) but if its swaying its probably massive variation in the temperature. As said above, can you confirm your water pump purchase with us? How did you bleed the coolant? Is your thermostat in correctly? what kind of thermostat? Do you have a no-spill funnel? (great for making it mess free and easy to bleed coolant!) here is an example!! Use on many cars. I have the older version with an opaque orange funnel, they improved it to be clear now.
also, importantly, WHAT kind of fan clutch did you use? can you show us a pic of where your fan is sitting relative to your shroud? did you put the fan the right direction (Should have "FRONT" on one side of it)

 

Thanks for the input and pointers.
In answer to AuroraGirls questions:
1.Once engine is warm, it moves from middle of gauge, (between R and M), to extreme right, the final white line before the red zone. It definitely drops in a manner characteristic and consistent with high RPMs.
2.I did check the function of the temp sender both grounded and ungrounded and it behaved correctly.
3.Got the water pump from AutoZone. At time of installation I confirmed it was exactly the same as the current water pump, including the direction of the fins.
4. I bled the coolant by running engine in driveway until bubbles came out. I continued to let the engine run and kept filling the radiator until it stopped dropping. I filled the overflow tank, installed the radiator cap and drove in order to create enough heating and cooling to draw coolant in. (I made sure the thermostat was installed with the little air bleeding opening at the top. I have checked several times and the radiator continues to maintain its coolant level.
5. I don't remember what kind of fan clutch. Believe I got that at AutoZone as well.
6. The an blade is installed so that when looking strait down from above, 1/2 is with in the shroud and the /2 width is outside. The blades are riveted to the arms and the rivet heads point forward. If the blade was turned around, none of the blades would e within the shroud. Pretty sure I confirmed the orientation when I installed it.

Now here is something to consider and it's embarrassing but true: I did have the gosh darn thermostat in backwards, but I corrected that and the temperature gauge didn't behave any differently.

Also, when it was running consistently hot, I pulled over and noticed that the overflow tank was full and dripping so that leads me to believe a clog somewhere or, perhaps a malfunctioning thermostat, though itt is new.

Thank you!

 

I am not sure about your engine but in the past ive installed a thermostat backwards and it actually crushed part of the thermostat meaning it couldnt operate properly. and did you quench the heater hoses and the radiator hoses while the heat was on high and hold the RPMs higher when trying to bleed? Thats part of the procedure for these trucks


Ive never owned a small block ford before, is your coolant bypass hose in proper order?


I also found this on bleeding trapped air in the service data:

1. "To bleed trapped air from cooling system, disconnect heater hose from water pump. Using 50/50 mixture of coolant and water, fill radiator until coolant flows from heater hose fitting at water pump. Reconnect heater hose."

Finally, the autozone fan clutch? was it the store brand? If so, its junk. Either reuse the OE if its in good shape or buy a motorcraft. I bought a autozone store brand for my 4.9. Absolute JUNK. the OE from 1996 is still on it now. Theres also a thermostatic spring that controls the fan clutch on the front of the clutch, if its not in the right spot it wont work. send a pic?

My vote is on air in the system based on everything thats been said.

 

House brand? Lifetime warranty?

I am certain, Autozone has some good parts, but Durajunk, Cardone, etc are just junk. Worth the extra money to buy something with a name you are familiar with.

 

ok if you used a no spill funnel make sure the rubber oring isn't still in there. happens a lot can cause some big issues. could also be a damaged fin. run the truck and watch the gauge. as it warms up feel both the upper and lower hose. if the upper gets really hot really fast you've either got a bad thermostat or it is installed wrong. if its gradual then cross that off the list. Next the bypass from the pump to the thermostat housing. if that is blocked or damaged in anyway it could be related to the problem as water would not be able to pass the thermostat and in these trucks that is a very important mechanic.

 

AuroraGirl:

You were dead on. I took my time refilling the cooling system. I even disconnected the bypass hose to the thermostat housing and filled from there in order to not have to wait for the thermostat to open up and burp out the air in the block. Colling system works perfect now.

Thanks for the advice.

 

I'd verify operating temp with an IR thermometer. Its possible the gauge is wonky or the temp sender or its connection is janky.