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I just replaced my reservoir on my 96 Taurus (72,000 miles) because of a massive leak. My old one had a crack in it, which drained all my coolant fluid. So I filled it back up. I have been checking afterwards for any other possible leaks and fluid loss and have not found one since. However, now my temperature gauge is acting up. Here's a video that I took while I was driving:


Sometimes it even goes higher to about 80% then back down to around 20% despite the cold weather here; it ranges from 40 to 50 degrees farenheit here in VA now. It did this before when I haven't changed my reservoir yet but mostly it stayed on the high side. Now I don't know what's doing this. Hopefully ya'll could help me out.

Thanks
 

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Cake monster
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I just replaced my reservoir on my 96 Taurus (72,000 miles) because of a massive leak. My old one had a crack in it, which drained all my coolant fluid. So I filled it back up. I have been checking afterwards for any other possible leaks and fluid loss and have not found one since. However, now my temperature gauge is acting up. Here's a video that I took while I was driving:

YouTube - 96 taurus temp fluctuation

Sometimes it even goes higher to about 80% then back down to around 20% despite the cold weather here; it ranges from 40 to 50 degrees farenheit here in VA now. It did this before when I haven't changed my reservoir yet but mostly it stayed on the high side. Now I don't know what's doing this. Hopefully ya'll could help me out.

Thanks
Time for a water pump.
 

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My 1st question what is the health and status of your cooling system? Any car that runs that cool would appear to me its missing a thermostat. And if its missing a thermostat why? A lot of thermostats are removed to solve overheating problems. If a car is overheating then why is it overheating?

I would pressure test the cooling system, look for additional leaks and get a Motorcraft thermostat. I have a 1997 Sable and replaced the radiator in DEC-2010. It was the original radiator, don't be surprised if your radiator is on its way out as well. Given the age of the car it will probably go at anytime.

Find a way to verify the gauge reading with actual temperature. If you can get and OBDII tool and check the engine temp reading electronically as well.

With my Sable the gauge stays at 1/3 the scale when the reaches 190F - 197F. Anything higher then 200F then it starts creeping toward HOT.

Don't be surprised if you have to spend a couple of hundred bucks to get the cooling system where its suppose to be.

Monsoon
 

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Discussion Starter #5
Thanks for the replies. I just inquired about a pressure test and a local shop would do it for $50. So far my mpg is averaging 20 and other than the temp fluctuation on the gauge, there has not been any problems or symptoms. Is this something important that I should take care of immediately? Or could I wait to deal with this symptom?
 

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I bet OP problem it was a bad thermostat. So probably yours too. Get a Motorcraft thermostat from Amazon.

Unfortunatelly, lots of people ask a question here, get a few pointers, probably one of them helps them and they never come back to say "thank you, THAT helped". Or "thank you, but it WASN'T that, it was THIS". Feedback is important on public forums like this, we all want to learn from eachothers experiences.
 

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Thanks SoNic67. I will give that a try. I replaced the Radiator over the weekend and it helped slightly. I think I will create my own thread with my findings to help others that might have been in the same shoes as me.
 

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Hey, has anyone solved Jason's issue? I have the exact same problem. New waterpump, flushed cooling system and most recently new thermostat. Started after new waterpump install. I am thinkng it is an air issue. Repeats like clockwork about every 1.5 minutes while driving exactly as in video. Goes to normal temp reading and then drops down to bottom of warm range (just above Cold mark).

Car runs normally, fan comes on, heat works fine, no noticeable issues except temp gauge fluctuation.
 

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Hey, has anyone solved Jason's issue? I have the exact same problem. New waterpump, flushed cooling system and most recently new thermostat. Started after new waterpump install. I am thinkng it is an air issue. Repeats like clockwork about every 1.5 minutes while driving exactly as in video. Goes to normal temp reading and then drops down to bottom of warm range (just above Cold mark).

Car runs normally, fan comes on, heat works fine, no noticeable issues except temp gauge fluctuation.
That looks like a bad thermostat. May be new, but new is not necessarily good. To go that cold says the thermostat is staying open, then closing, but way too slowly.

-chart-
 

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I just replaced my reservoir on my 96 Taurus (72,000 miles) because of a massive leak. My old one had a crack in it, which drained all my coolant fluid. So I filled it back up. I have been checking afterwards for any other possible leaks and fluid loss and have not found one since. However, now my temperature gauge is acting up. Here's a video that I took while I was driving:

YouTube - 96 taurus temp fluctuation

Sometimes it even goes higher to about 80% then back down to around 20% despite the cold weather here; it ranges from 40 to 50 degrees farenheit here in VA now. It did this before when I haven't changed my reservoir yet but mostly it stayed on the high side. Now I don't know what's doing this. Hopefully ya'll could help me out.

Thanks
Others have made good suggestions. Here is what i would do. heat it up until its doing the flucutuation. stop car. open the hood. look and listen closely for any hissing noises, steam whiffs, or other leaks or wet spots.
If your cooling system is not holding pressure, it will tend to overheat.
You did change the cap on the degass tank when you changed it?

I have had pin hole leaks many places. from cracked radiator plastic tanks
to the heater core bypass hose T fittings.

The problem with the shop pressure test is that its static with the car sitting still. Unless its really a goner, its not going to tell you much.
What i did is make a ghetto harbor freight pressure gauge for about $10
and left it inserted in the degass tanks small line. Then i could
open the hood and check it at any time if i detected an issue.

Its also possible if you have a two speed radiator fan, that the low speed
is not working. some had a resistor, some had two windings for slower
speed. You would have to do some more research on that.
 

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I bet OP problem it was a bad thermostat. So probably yours too. Get a Motorcraft thermostat from Amazon.

Unfortunatelly, lots of people ask a question here, get a few pointers, probably one of them helps them and they never come back to say "thank you, THAT helped". Or "thank you, but it WASN'T that, it was THIS". Feedback is important on public forums like this, we all want to learn from eachothers experiences.
1+^ Feedback is crucial to help others. And always buy a Motorcraft brand thermostat and reservoir tank cap, no aftermarket or off-brand. There are some parts you'll want to spend a little more on for OEM quality, and these are two of them. I recently bought and installed an aftermarket reservoir tank because mine was cracked, and I immediately trashed the cap that came with it, and replaced it with a brand new Motorcraft. $31 for an off-brand tank and $6 for an OEM cap was quite a bargain.
 

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That looks like a bad thermostat. May be new, but new is not necessarily good. To go that cold says the thermostat is staying open, then closing, but way too slowly.

-chart-
What I found out when I had my temp gauge fluctuations, and it happened a couple of times, was that the reason was some pressure loss. It was cracked rad at one time, bad cap at another. The worst to fix was a pinhole in the upper hose.
Stan
 

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What I found out when I had my temp gauge fluctuations, and it happened a couple of times, was that the reason was some pressure loss. It was cracked rad at one time, bad cap at another. The worst to fix was a pinhole in the upper hose.
Stan
Yea, i have had versions of all of the above. Loss of pressurization = overheating and boiling over.

I had a radiator side tank crack
i have had degass tank cap leak
I have had degass tank crack and leak
i have had heater core bypass hose T leak
I have had a failsafe thermostat FAIL SAFE.
(which means it sticks all the way open, you'll freeze in the winter)
I have had heater blower motor fail in the winter
(crawled under the dash in below zero weather to fix that one)
I have had air switching vents that it comes out of depending on how
fast the motor was revving (leaking vacuum motor in hvac)
Lost count of how many Vulcan water pumps i have changed
(note: they are NOT all the same)
Once had the serp belt idler bolt launch and put a hole in the washer tank
of my old 93


fun, fun.
 

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Bad thermostat.. mine was doing the same.. changed and all is solved!

To help the issue don't indicate changed the thermostat, idicate if you swapped it with a Motorcraft thermostat otherwise, some of us may assume you picked one up at your local retailer a non-Motorcraft thermostat.


Monsoon
 

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Anything that is labeled as "cracked" or a "leak" will show-up with cooling system pressure test. Your car is the best test platform for diagnosing problems provided you have the correct tools and a good technique for troubleshooting.

I have seen overheat problems caused by an intermittent or borderline thermostat. What is an "intermittent thermostat"? An intermittent thermostat is a thermostat that is closed when its cold and opens only slightly once warmed up.

This can be seen with the temperature gauge, at idle the engine will begin to overheat, water pump moves slowly here moving coolant slowly as well, like at a stop light but once the car gets moving water pump moves the coolant more quickly and then the guage drops down to the normal range. This oscillation of the temperature gauge is not normal.

If you have no cooling system leaks be aware of this "borderline thermostat" issue. Your temperature gauge could be your best tool to diagnose this problem.

Monsoon
 

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Just to give a bit more background let me say that cooling system has been totally flushed, new waterpump, and new thermostat (that opens properly as tested in boiling water with temp reading and I actually tried 3 of them at different temp ratings and they all do the same), used check valve type (last time) and installed at 12 Noon position. All of these system renewals did not alter the behaviour. I no overheating issues as it runs in a perfectly normal zone according to thermostat rating (tried 3, 180, 192, 195). It just drops back toward the Cold(er) side by about 50% of the normal running range every 3-4 minutes while on the highway and less often while around town. It seems the more rpm you drive the more often the fluctuation occurs. It never fluctuates while it is coming up to normal temps, only after (seems like when the thermostat opens) it is a full operating temperature.

Now I may have a small leak (pinhole) in coolant reservoir as I did hear a high pitched whistle occuring periodically while driving (only for a about 5 or 6 secs) then it disappears. It has a few very small cracks on the top and added a bit of sealant to it just in case they were leaking air and to help isolate the issue (see if the sealant would stay sealed or blow off), now I have not had the whistle sound recently and the system is holding pressure as the cap is always pressurized even after it has cooled down. I did check the coolant switch and it was outside of the recommended resistance settings (not a lot different, but not according to manual) and intend to replace it next just because there is not much left to do on this system, so if it is not the problem we will be living with the mystery untill something really blows. Heat works great and has no detectable effect on anything else. You can't even detect a decrease in the heater air when it occurs so it is like a false reading. I can't even imagine why the sensor would register that much of a drop even if it encountered an air pocket as I don't think it would cool down that much even with the very hot air in the water jacket. So methinks it just has to be one wonky sensor switch, at least I hope it is.

Listening to your posts I am wondering about a temporary loss or fluctuation in pressure (not a total loss of pressure, but maybe a drop) may be causing the gauge fluctuation too. I have never seen a coolant system behave like this in all my years (my first Ford since 1966 Mustang), but maybe the Taurus has some unique behaviour or sensitivity to pressure drops which allows a very quick temperature fluctuation if there is a pressure change. However, I would think that pressure loss would push the temperature higher than the normal range and that is not the case here. Stan's situation might be close to mine if I knew whether his situation stayed in the normal range and dropped (like mine) or actually ran hotter and dropped (which is not my case).

Good idea on connecting an OBDII reader as I have one I could dig out and actually monitor the engine temp to see what it is doing. Now I have to figure out how to use it.

It's too bad the first poster here did not post his solution as his video is exactly what my gauge is doing and it is very likely my problem too.

Thanks fellows for the input!
 

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Just to give a bit more background let me say that cooling system has been totally flushed, new waterpump, and new thermostat (that opens properly as tested in boiling water with temp reading and I actually tried 3 of them at different temp ratings and they all do the same), used check valve type (last time) and installed at 12 Noon position. All of these system renewals did not alter the behaviour. I no overheating issues as it runs in a perfectly normal zone according to thermostat rating (tried 3, 180, 192, 195). It just drops back toward the Cold(er) side by about 50% of the normal running range every 3-4 minutes while on the highway and less often while around town. It seems the more rpm you drive the more often the fluctuation occurs. It never fluctuates while it is coming up to normal temps, only after (seems like when the thermostat opens) it is a full operating temperature.

Now I may have a small leak (pinhole) in coolant reservoir as I did hear a high pitched whistle occuring periodically while driving (only for a about 5 or 6 secs) then it disappears. It has a few very small cracks on the top and added a bit of sealant to it just in case they were leaking air and to help isolate the issue (see if the sealant would stay sealed or blow off), now I have not had the whistle sound recently and the system is holding pressure as the cap is always pressurized even after it has cooled down. I did check the coolant switch and it was outside of the recommended resistance settings (not a lot different, but not according to manual) and intend to replace it next just because there is not much left to do on this system, so if it is not the problem we will be living with the mystery untill something really blows. Heat works great and has no detectable effect on anything else. You can't even detect a decrease in the heater air when it occurs so it is like a false reading. I can't even imagine why the sensor would register that much of a drop even if it encountered an air pocket as I don't think it would cool down that much even with the very hot air in the water jacket. So methinks it just has to be one wonky sensor switch, at least I hope it is.

Listening to your posts I am wondering about a temporary loss or fluctuation in pressure (not a total loss of pressure, but maybe a drop) may be causing the gauge fluctuation too. I have never seen a coolant system behave like this in all my years (my first Ford since 1966 Mustang), but maybe the Taurus has some unique behaviour or sensitivity to pressure drops which allows a very quick temperature fluctuation if there is a pressure change. However, I would think that pressure loss would push the temperature higher than the normal range and that is not the case here. Stan's situation might be close to mine if I knew whether his situation stayed in the normal range and dropped (like mine) or actually ran hotter and dropped (which is not my case).

Good idea on connecting an OBDII reader as I have one I could dig out and actually monitor the engine temp to see what it is doing. Now I have to figure out how to use it.

It's too bad the first poster here did not post his solution as his video is exactly what my gauge is doing and it is very likely my problem too.

Thanks fellows for the input!
If you have ANY cracks in the degass tank, REPLACE IT! replace the lid
too.

Like i said before, check for pinhole leaks after the car is good and hot
and shut off. Mine had a pin hole in the T fitting of the heater core
bypass hose. It was NOT easy to find. If you coolant was bad, ANY
metal coolant tubes may rotted from the inside out and ready to give way.

Start with changing the degass tank, and go from there.

Also, your OBD2 reader would have to do live data to read the temp
real time. Cheaper ones won't

One other thought, maybe you radiator hoses are spongy and collapsing
causing cooling flow issues?
 

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To help the issue don't indicate changed the thermostat, idicate if you swapped it with a Motorcraft thermostat otherwise, some of us may assume you picked one up at your local retailer a non-Motorcraft thermostat.


Monsoon
Bought a failsafe Autozone t-stat.. about $8
Flushed and filled with 50/50..
Sorry for no clarification!
willie
 
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