Temperature Fluctuations

[ddenton749]

1993, 4.0L, Auto, 4WD. This problem started about a month ago. When driving at a normal steady cruise, the temperature rises up to about the “A” in “NORMAL”, stays there for only a second, then drops back down to below the “N”. The needle will stay at the low end for a minute or two and then rise back up to the “A”, where it stays for a second, then drops back down below the end. It continues to cycle this way and never reaches equilibrium.

I know it isn’t a bad sending unit, gauge, etc. because I can feel the difference in the air temperature coming out of the vents when the heat is on.

In the second week of February I replaced the water pump because it was leaking. I also replaced the thermostat, the serpentine belt, and all of the hoses. The temperature fluctuations started around the end of January, before I replaced the water pump.

Any ideas?

At no time has the temperature gone above the “A”, but its still winter and I’m worried what will happen once the weather turns warm again. I don’t spend a lot of time idling, but the gauge seems to stay at the low end at idle.

 

[MNHawk]

It's not uncommon to get a faulty T-Stat. Did you replace it with a 195, 180, or 165 degree t-stat? Also have you checked your cooling fan (manual or clutch)? If clutch, the fan clutch could be bad and not working the way it should. Which would cause the eratic temp jumping (but a faulty and/or sticking t-stat could do the same).

If the fan checks out to be fine, it would be a good idea if you change the t-stat out again and to flush your system. If its been under 30 days most part stores will warranty it out with out any questions.
You would be surprised at what can build up inside the cooling system.

 

[L B THOMPSON_6]

I had the same problem and my son changed the thermostat. Afterwards I had the same problem. I removed the new thermostat and tested it in water. It was fine, so I inspected the thermostat opening on the motor and found a small piece of the original Ford thermostat down in the opening. Apparently when you raised rpm enough it would come up and partially block the flow and then fall back causing a spike in temp. I removed it, put thermostat in and problem was gone. Just a thought, hope it helps.

 

[MNHawk]

I had the same problem and my son changed the thermostat. Afterwards I had the same problem. I removed the new thermostat and tested it in water. It was fine, so I inspected the thermostat opening on the motor and found a small piece of the original Ford thermostat down in the opening. Apparently when you raised rpm enough it would come up and partially block the flow and then fall back causing a spike in temp. I removed it, put thermostat in and problem was gone. Just a thought, hope it helps.

You would be surprised at what can build up inside the cooling system.

This is the exact reason why I stated this.

 

[ddenton749]

No kidding?

I had the same problem and my son changed the thermostat. Afterwards I had the same problem. I removed the new thermostat and tested it in water. It was fine, so I inspected the thermostat opening on the motor and found a small piece of the original Ford thermostat down in the opening. Apparently when you raised rpm enough it would come up and partially block the flow and then fall back causing a spike in temp. I removed it, put thermostat in and problem was gone. Just a thought, hope it helps.

You're kidding! This same thing happened a few years ago with this same ex, but the problem went away on its own. It would make a lot of sense. Would that explain why it seems so difficult to get the air out of the cooling system?

 

[MNHawk]

You're kidding! This same thing happened a few years ago with this same ex, but the problem went away on its own. It would make a lot of sense. Would that explain why it seems so difficult to get the air out of the cooling system?

I installed one of those Prestone Flush kits to aid in removing the air from the system. Just install a short hose to a can so that the over flow does not spill on to the manifolds. Decided this due to it seemed to be the highest point of the whole system.

 

[mikeinri]

You might also look at the orientation of the "weep hole" of the t-stat. See the post below.

http://www.explorerforum.com/forums/showthread.php?t=180163

Mike

 

[ddenton749]

The thermostat is in correctly and the air bleed hole is at the top.

The other thing I just remembered is when I run the engine with the radiator cap off, the coolant level drops and then surges to the point where it overflows out of the top of the radiator.

 

[lilbeefy]

i suspect air in the coolant system. try burping your ex. then give it a few weeks.