Water overflows at 180F.

[ErniesRedGT]

Hi everyone I have a 96 GT i just purchased two weeks ago. It has an aftermarket mechanical water temp gauge. As soon as the gauge reads 180f
antifreeze starts overflowing from the plastic cap. I have replaced the radiator, all hoses, thermostat, and the cap itself, and it still does it.
Also, when the temp reads 140f and above if you squeeze the upper hose its
hard as a rock from the pressure. I really dont know what to do next, any help will be appreciated.

 

[oxfordgt]

Could be a blown headgasket. Do a compression check.

 

[ErniesRedGT]

I thought about that, but the funny thing is if i run it with the ac on i can drive it all day and the temp wont go past 170f. Even in stop and go traffic.
Maby it has something to do with that fact that the ac forces the fan on.
Does someone know at what temp the fan is suposed to start up with the ac off?

 

[Rickyll7]

Hi everyone I have a 96 GT i just purchased two weeks ago. It has an aftermarket mechanical water temp gauge. As soon as the gauge reads 180f
antifreeze starts overflowing from the plastic cap. I have replaced the radiator, all hoses, thermostat, and the cap itself, and it still does it.
Also, when the temp reads 140f and above if you squeeze the upper hose its
hard as a rock from the pressure. I really dont know what to do next, any help will be appreciated.

You didn't do something weird like put the thermostat in upside down, did you? The longer part goes down.

I can't think of anything that would cause those symptoms.

Weird!

Oh! I think I know what your problem could be. You do have 50/50 coolant in there right? What altitude are you at?

 

[wmburns]

Test low speed fan

Does the fan run at all when the AC is not on? Recommend testing the low speed fan. Jumper directly to battery to confirm fan works. We know the high speed fan works (turns on when AC is on).

Do you have an ODB2 scanner? What is the coolant temperature reported by the PCM? Does the dash guage work? Remember that the 96 has two temperature sensors. Are they both connected? Could the original owner have removed one of the temperature sensors to install the mechanical unit?

Any check engine codes? Custom tune?

180 degress is way too low to have coolant blowing out the de-gas bottle. In fact, 180 is low normal operating temperature. This shouldn't be happening until 220+. Also, 140 degrees is way too low for normal operating temperature. Is the mechanical gauge accurate?

Are you sure it is not over filled? Any other mods?

 

[Rickyll7]

Water will boil at a much lower temperature at higher altitudes.

 

[Kilgore Trout]

These cars do not blow head gaskets, I suspect fan issues.

 

[oxfordgt]

These cars do not blow head gaskets, I suspect fan issues.

Since when? I have fixed 5 blown head gaskets 2 of them were stock engines.

 

[Kilgore Trout]

Since when? I have fixed 5 blown head gaskets 2 of them were stock engines.

I am sure there is a story behind each of those anomalies. It is exceedingly rare for a modular engine to blow head gasket.

 

[oxfordgt]

Water will boil at a much lower temperature at higher altitudes.

Water boils at a much higher temp in a pressurized system. That is why a stock system is pressurized to 16psi. If the pressure is higher then 16psi it will come out of the overflow/cap.

 

[wmburns]

IMO, there is something strange going on here.

First, the OP reported that the car runs fine with the AC on. When the AC is on, the PCM forces the high speed fan to run. The fact that the car does not overheat when the high speed fan is running tells me the cooling system is basically functional.

This also says to me that it is not a head gasket problem as a bad head gasket would not care if the AC was on or off.

However, the stock t-stat is 190-193 degrees. Therefore, blowing coolant out the de-gas bottle at 180 degrees is clearly not correct. Either the guage is wrong or the radiatior pressure cap is venting way too low.

My hunch is that a single speed V6 fan was used in a dual speed V8 application. The PCM is calling for low speed fan and the fan is simply not running.

The trick is to find out why the fan is not working. Is there a problem with the fan itself or in the control circuts to the fan. The OP is going to need to run some tests and post the results.

 

[ErniesRedGT]

I live in Florida so altitude is not an issue. I have never seen the fan run with the a/c off, and I really don't trust the aftermarket mech temp gauge. It just doesn't seem to be very consistent. When it reads 180f I think it is warmer than that. As far as the stock gauge, someone installed white face gauges. and I don't think they inserted the needle to the temp gauge correctly afterwards. Also, it has a 170 thermostat in it, if that helps with information. I'm trying to insert some pics of the setup that is under the hood for the aftermarket gauge, so let me know if it looks like it was done right to you guys. Thanks for any help.

 

[Rickyll7]

Water boils at a much higher temp in a pressurized system. That is why a stock system is pressurized to 16psi. If the pressure is higher then 16psi it will come out of the overflow/cap.

True, I forgot about that. Also, the high speed fan should eventualy come one even if the low speed operation is not functioning. The high speed fan should come one before the engine over heats. I dont think that temp sensor is working right or the cap is messed up, or both. There is no reason for 50/50 coolant to boil over at 180 degrees F and 16 psi. One or both of those numbers isnt actualy happening.

 

[Rickyll7]

I live in Florida so altitude is not an issue. I have never seen the fan run with the a/c off, and I really don't trust the aftermarket mech temp gauge. It just doesn't seem to be very consistent. When it reads 180f I think it is warmer than that. As far as the stock gauge, someone installed white face gauges. and I don't think they inserted the needle to the temp gauge correctly afterwards. Also, it has a 170 thermostat in it, if that helps with information. I'm trying to insert some pics of the setup that is under the hood for the aftermarket gauge, so let me know if it looks like it was done right to you guys. Thanks for any help.

Get a scanner and read the digital read out for the engine coolant temp. I bet its over heating becasue your fan isnt coming on at all, neither high or low speed.

Oh, and as matters of safety... I would cover up that positive terminal on the alt. with something and you are missing the upper bracket that holds the alt. to the coolant cross over tube. I've heard of the lower bolts breaking off if you dont have the upper bracket.

 

[wmburns]

I see a couple of issues here. The height of the tee is so great, there is a real possibility of air being trapped in the tee. This will cause the sensor to read the temperature of the AIR and not the COOLANT. Some method will be needed to ensure the sensor is actually touching the coolant or the PCM will never get a true read.

This may explain why it is coolant is venting at 180 degrees as the actual temperature is much higher. Consider under normal conditions, 180 is not high enough for the PCM to even call for the fan to run.

This also points out how all of this stuff has to work together. If a lower temperature t-stat is used but the PCM is not re-programmed, then the car will never reach the correct operating temperature. This has the t-stat opening too soon and the fan never runs. The results will be wild temperature swings depending upon outside temperatures and how the car is operated (AC on/off, how fast ect).

There is also no indication of the fan tests. The low speed fan uses the R/O wire. The high speed is O/LB. The ground return is BK (black). Disconnect the fan connection. Jump the R/O and black wires directly to 12 volts. The low speed fan should run.

Next jump the O/LB and Black wires directly to 12 Volts, the high speed fan should run. There should be an obvious difference in fan speed. Post the results.

If the fan only has two wire colors, then the wrong fan has been used.

Once we have the results, will need additional tests to further narrow the problem down as I think there is more than one.

On first impression, my vote is the primary problem is air in the tee resulting in a chronically low sensor reading. The PCM never calls for the fan to run and a slow overheat is the result.

Consider using the drain taps on the side of the block for the mechanical temperature guage. Restore the PCM temperture sensor to its original location. This will have the tip of the sensor in the coolant stream thus ensuring an accurate reading.

 

[ErniesRedGT]

Consider using the drain taps on the side of the block for the mechanical temperature guage.

Thanks for your help, I'm definitely going to try the tests with the fan wires like you suggested, I think you are on to something. The only thing is, I don't understand what you mean by the drain taps, do you mind elaborating on that a little? Also, when you mentioned a slow overheat, you nailed that issue because it really does take a long time for it to overheat, at least 15 mins of normal driving, even with the fan not running. Another thing, if I'm on the interstate it won't overheat at all, I even drove it down from Tampa, which is almost 3 hours away. But the moment I start hitting stop and go traffic after I get off the interstate it will start overflowing. This is all with the fan never turning on.

 

[Rickyll7]

Just noticed something else in that pic. The wiring to the factory temp sensor looks sketchy. I would check that out.

 

[wmburns]

Block drain taps

Look on the side of the block under the freeze plugs. You should see a threaded hole with a plug. This is the coolant drain plug. This can be used as an alternate sensor location. Note, the temperature readings will be somewhat lower than the intake manifold cross over. However, any sensor installed will be in direct contact with the coolant and provide a reasonable reading.

Consider that the PCM turns off the fan anytime the car's speed is above 45 MPH. The car does not overheat on a long drive because above 45 MPH there is plenty of air flowing through the radiator naturally.

Once in stop/go driving, the fan is needed.

 

[oxfordgt]

Are you guys forgetting this is a non-pi motor? The sensor on the driver side only controls the stock gauge. The sensor on the passenger side is the one the computer looks at to see engine temps.

 

[ErniesRedGT]

I did the low and high fan speed test straight to the battery and both speeds work. The only thing that concerns me is that the wires I used to run the fan to the battery got hot during the test, not so hot that I couldn't touch them but they felt pretty warm to the touch in a matter of seconds. I'm wondering if its a good idea to just run the fan to come on whenever the ignition is turned on because it sounds to me like it might be the electrical fan box with the relays in it thats gone bad, and I don't have the money right now to purchase the new one. If you guys can let me know where to find a good source for the positive wire to turn on and off the fan with the ignition, I would appreciate it. By the way, I ran the negative cable to the negative post on the battery. Should I have just put it the ground source like the chassies?