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Discussion Starter · #1 ·
About a week ago I changed the T-stat in my car and replaced the upper and lower rad hoses. I filled the car with coolant and bled the system via the chilton instructions.

So I ops check it, it runs good , no overheating etc T-stat opens... The next day I come out to check the coolant levels, coolant in the resavoir is where it should be and coolant is up to the top of the filler neck in the radiator as it should be.

So I am driving the car and after about 20 minutes the temp gauge jumps up to the A in "NORMAL" hangs out and bobs back and forth a bit then drops back down between the N and O.

with a 195 deg T-stat, the car has always regestered between the N and O in the word NORMAL on the gauge. the spike happens about every 20 min the gauge will spike or flux then go back to where it should be and stay there

What could be causing this ? air? wiring? is there a sure-fire way to get all the air out of the cooling system without a pressure tester. Also, where is the temp sending unit located? car is a 1994 ,3.0 Vulcan

Any input/ pics would be appreciated
 

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It is normal to see some fluctuations in the temp guage as it is the T-Stat opening and closing.

Could be the temp sensor on its way out.

I do know on the SHO you can get T-Stats with the jiggle valve to help air go by. Without it it casues problems. Did yours have it?
 

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Discussion Starter · #3 ·
the old original T-stat had one but there was no jiggle valve on the new one. it was an aftermarket one . I was told it wasen't needed with the newer T-stats as it was internal on the aftermarket design.
 

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Check the electrical connector on the temp gauge sender (not the ECT). May be loose or have some corrosion.
 

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the old original T-stat had one but there was no jiggle valve on the new one. it was an aftermarket one . I was told it wasen't needed with the newer T-stats as it was internal on the aftermarket design.
I'm afraid you were lied to. In fact, on my vehicles, the only thermostats that lasted or worked reliably were the motorcraft ones. The aftermarket ones open and close at the wrong temps. You problem is very familiar to me, I think your solution is to replace the thermostat with a Motorcraft unit. They are just better.
 

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With the newer cars and trucks today every time I change out coolant or tranny fluid I take a clean washtub bucket and let the coolant drain into it, measure it, than make absolutely sure I get the right amount back in. I have noticed especially on Ford products that it is very hard to get the right amount of coolant/tranny fluid back into the system. I changed my coolant in my F250 diesel measured it and couldn't get what I took out back in even with a tool called an air lift. Tool pumps air out of system. I would drive and monitor it very closely, refill as necessary and don't let it overheat.
 

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Discussion Starter · #10 ·
I'm afraid you were lied to. In fact, on my vehicles, the only thermostats that lasted or worked reliably were the motorcraft ones. The aftermarket ones open and close at the wrong temps. You problem is very familiar to me, I think your solution is to replace the thermostat with a Motorcraft unit. They are just better.
I actually had this same problem with the old T-stat(with the jiggle valve) but it was way way worse. that is one of the reasons I changed it to begin with. I thought the fluctuations were due to that...this is actually a reoccuring porblem... let me give you guys a brief history.

- Acquired the car in Spain from an Army guy -Temp gauge didn't flux

-heatercore on car went out in Spain (couldn't replace at the time so I bypassed the Heatercore) Problem started...attributed it to air in the system due to bypassing the heatercore

- get back to the states, had a professional mechanic replace the Heater core (did not read the writeup on this site:rolleyes2:) Mechanic flushed and refilled system...Problem still there

-brought the car back due to a leaky heater core hose. System fixed and refilled..temp gauge still fluxing but it is worse now.

- 2 weeks later get a hole in the lower radiator hose . decide to replace the T-stat since I was replacing the hose anyhow.....refill and bleed system according to Chilton replact T-stat with A-zone one ..problem still there but no where near as bad as it was.

- So here is where I am at now, I am sure the Motorcraft T-stat would be better...OEM is always better but I do not think it is the cause of this problem.

- That is why am thinking air or wiring now.
 

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Discussion Starter · #11 ·
With the newer cars and trucks today every time I change out coolant or tranny fluid I take a clean washtub bucket and let the coolant drain into it, measure it, than make absolutely sure I get the right amount back in. I have noticed especially on Ford products that it is very hard to get the right amount of coolant/tranny fluid back into the system. I changed my coolant in my F250 diesel measured it and couldn't get what I took out back in even with a tool called an air lift. Tool pumps air out of system. I would drive and monitor it very closely, refill as necessary and don't let it overheat.

You may be on to something with this! My other car ...2003 Mustang Cobra, almost needs a special tool to bleed the cooling system It is a total PITA to do without that tool ...but it is possible, I was just hoping that a 1994 Ford taurus cooling system would be a bit more simplified than a newer ford...I am starting to think it isn't LOL
 

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I have changed coolant on G2 vulcans many times (most recently last week on my "new to me" 95), and never had a problem with air bubbles or filling the sytem completely.
 

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You may have a problem with the water pump, not the thermostat. Its kinda strange, but some other Fords will sometimes have problems with fluctuating temps due to worn impeller blades that cavitate.
 
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