Wandering Temp Gauge - Another

[Elendil]

Installed a new water pump and thermostat on my '94 Explorer 4.0 today. Now, I am experiencing rapid fluctuation in temperature from the 'N' to 'R' in normal - from one minute to the next. This is city driving, haven't had her on the highway yet.

With my old setup (original water pump and thermostat), temperature would move very slowly between 'N' and 'R' with obvious engine strain / release, but usually sat like a rock on 'O'.

Everything was installed correctly, the thermostat is opening, etc... anyone have ideas? Here are some of my guesses:

1) Air in the system (?)
2) Thermostat (supposedly high quality, 195 degrees) opens and closes quicker than my old OEM one, causing more variation - maybe my old thermostat was stuck partway open?
3) Need new radiator cap since I no longer have a coolant leak
4) New water pump is not working 100%

Thanks for your input - this is killing me.

 

[Steved]

I am experiencing the same symptoms you are. My X is also a 94, not that that has anything to do with it. I noticed that when I don't have the heater on the temp quage is pretty steady.
I tried to "burp" the system but no change. I haven't tried a new cap yet.

 

[TPLYNCH]

1 and 3 are your best bets for the problem

 

[BradE.]

How exactally did you try and burp the system?

Here is the method I use.

1. Back radiator cap off to first position, or just take it off.
2. Fill radiator to just below filler neck
3. Start truck and run at 2K RPM for 3 minutes with the heater on the max setting.
4. Shut off engine and check radiator, top off as needed.
5. Restart Truck and run at 2K RPM until thermostat opens with heater on max ( can sometimes take 15 minutes or more) , then let truck run a few mintues once the thermostat has opended.
6. Shut off truck and top off radiator and recovery.

That's it. Make sure to check the radiator and recovery the next morning and top it off.

 

[Elendil]

Problem solved (I think). Here's what I did... luckily it was fairly simple:

1) Flushed the coolant
2) Burped my baby really good (running at idle, with the rad cap off, for about 20 minutes - pressing on the top of the upper radiator hose every once in a while, felt / found a lot of trapped air)
3) Made certain my fan clutch was tight

Everything is great so far, sits on O. I notice a tiny fluctuation (between N and O) with the heater on, but nothing I'm going to worry about.

Also bought a new radiator cap for the heck of it... only $6 and my other is original equipment. Haven't put it on yet... so wasn't part of the fix.

 

[Elendil]

steved, have you used a cleaner on your system? Checked your heater hoses?

What does your gauge wander range between with the heater on?

 

[Steved]

I don't think my shop used a cleaner but I'm not sure. My water pump went bad and I had that and the t-stat replaced. Since then the guage wonders . At first it was from the "N" to "R" or "M" but lately it goes the range of NORMAL.
Seems like when I turn the heater off the needle stays pretty stable at the r and m. I haven't found a cap yet to try.

 

[Elendil]

Seems to me that changing the pump, etc. got a lot of air in the system which is taking its time to work out. I know you said you burped your rig already, but maybe checking that top radiator hose again would help...

I just returned from a 1200 mile trip on my new pump and thermo. After a long day of driving, I would let the engine cool, remove the rad cap and physically squeeze the top radiator hose at its highest point.

Without fail, I got air burping noises coming from the radiator. Each time I did this, the gauge wandered less and less - even with the heater on. After doing this, the wandering would improve. Now, my squeezes yield less and less air than they used to... good, I hope.

I also notice the gauge would sometimes start to wander after driving for a few hours - but after I stopped to get gas or something, it would run rock-solid on 'O'.

I got a new radiator cap too - didnt seem to help. Just to make sure, do you know what temperature the stat your shop put in is rated at? OEM is 195 degrees...

I'll keep working on this problem - keep me posted if you come up with some dufferent ideas / solutions.

 

[DEide]

Not sure about the 94 but the 96 has the termostat sitting vertical. If it is make sure the small hole in the termostat is on the top when you install it. Any air in the motor will exit this hole and not build up kepting the pellet on the termostat in the trapped air. It needs to be in the coolant to work.

 

[Elendil]

Yep, I installed the thermo with the little valve thing at 12 o'clock. Seems like most who have the same problem did so as well...

The air in my hose is, of course, on the radiator side of the thermostat - bleeding out through the thermo ok, but getting stuck at the cooling system's high point.

Goofy stuff, but it's getting better (for me).