Georgia Fiero Club Forum

All Things Fiero => Tech Tips, Tech Questions => Topic started by: GTRS Fiero on September 10, 2020, 04:34:43 pm

Title: Overheat?
Post by: GTRS Fiero on September 10, 2020, 04:34:43 pm: Here are the facts:
1. The temp gauge intermittently reads hot, sometimes to the red
2. The indicated temp can read hot while driving at speed, or while slow/stopped, but usually is a slow/stopped thing
3. The temp gauge has been calibrated, and is believed to be correct
4. When the temp is reading high on the gauge, the temp on the sensor frame does read high, using the laser thermometer
5. No change, with the shield installed or not
6. No change, with the thermostat installed or not, although different thermostats have been tested
7. The CTS reads 188 or 189 (laser thermometer and ECU), even when the gauge reads hot
8. The coolant fan does come on on occasion
9. The temp gauge sometimes jumps around, sometimes as much as 3 tic marks
10. The coolant system has been flushed and burped 3 times, with no change

Other relevant facts:
1. No temp issues, prior to swap
2. The radiator and coolant hoses have been replaced, still no change
3. The car can sometimes be driven for hours, with the temp staying normal

Any ideas?
Title: Re: Overheat?
Post by: TopNotch on September 10, 2020, 06:05:27 pm: No mention of the water pump in the above, so I have to ask -- Do you know what kind of impeller it has?
Title: Re: Overheat?
Post by: GTRS Fiero on September 10, 2020, 06:30:02 pm: Good question. I have been thinking about that. The pump I left to be installed, back in 2016, had a metal impeller. Lots of my parts that I had bought and left to be installed somehow vanished. No, I don't know. The water pump was replaced. That I do know.

Are these symptoms of an impeller that isn't turning?

I did not want to mention the water pump, because that could be leading...
Title: Re: Overheat?
Post by: TopNotch on September 10, 2020, 07:00:31 pm: Quote from: GTRS Fiero on September 10, 2020, 06:30:02 pm
Are these symptoms of an impeller that isn't turning?
I've never had a plastic impeller, so I'm not sure. They say it works when the pump is cold and starts slipping when it warms up.
Title: Re: Overheat?
Post by: GTRS Fiero on September 10, 2020, 07:01:23 pm: This one is just random, for the most part.
Title: Re: Overheat?
Post by: scottb on September 10, 2020, 07:03:43 pm: I'm wondering if it still has air trapped somewhere...... did you drill a small hole in the thermostat?
Title: Re: Overheat?
Post by: GTRS Fiero on September 10, 2020, 07:05:19 pm: No, but I did run about 150 miles, without the thermostat.
Title: Re: Overheat?
Post by: scottb on September 10, 2020, 07:46:47 pm: Quote from: GTRS Fiero on September 10, 2020, 07:05:19 pm
No, but I did run about 150 miles, without the thermostat.

Was it still showing hot?
Title: Re: Overheat?
Post by: GTRS Fiero on September 10, 2020, 07:52:26 pm: Randomly, yes. Mostly, it ran cold.
Title: Re: Overheat?
Post by: GTRS Fiero on September 10, 2020, 07:55:30 pm: I've been saying it's a 195-degree thermostat, but it's a 180-degree thermostat.
Title: Re: Overheat?
Post by: scottb on September 10, 2020, 08:59:21 pm: I am not an expert mek-a-nick but if it is not an air bubble it very well could be the waterpump impeller slipping on the shaft
Title: Re: Overheat?
Post by: GTRS Fiero on September 10, 2020, 09:01:48 pm: >:(

Just what I need.
Title: Re: Overheat?
Post by: GTRS Fiero on September 10, 2020, 09:28:28 pm: How can I test if the impeller is slipping, without remiving the water pump?
Title: Re: Overheat?
Post by: GTRS Fiero on September 11, 2020, 06:48:54 pm: I guess that answer says it all. Pulling the water pump. The owner of the space where my Fiero is is losing his patience. He wants my Fiero out of there. Me, too.
Title: Re: Overheat?
Post by: GTRS Fiero on September 12, 2020, 01:54:58 am: In the coolant path, where is the CTS, in relation to the temp sensor? Does the coolant come through the engine, through the temp sensor, then through more engine, through the CTS, and out the thermostat housing?
Title: Re: Overheat?
Post by: Fierofool on September 12, 2020, 08:16:47 am: The CTS is in the neck of the thermostat housing. The gauge/light temperature sending unit is in the left front corner of the cylinder head, just in front of the thermostat housing. It's possible to swap places with them if the wiring harness has been messed with enough that the wires can be extended.

First, verify that your gauge is calibrated correctly. With no power applied, the needle sits on the bulb of the thermometer symbol. With engine cold and ignition ON, the needle should move to the 100 mark. Testing temperature with an IR thermometer, focus the beam on the brass base of the sending unit. It should be very close to the correct temperature. Verify your gauge agrees.
Title: Re: Overheat?
Post by: GTRS Fiero on September 12, 2020, 08:26:01 am: Well, the gauge was about 90 degrees lower. The gauge has been calibrated.

I wanted to verify the coolant path, relative to the sensors. Basically, is the CTS at the coolant exit from the engine, and the temp sensor while the coolant is in the engine?
Title: Re: Overheat?
Post by: Fierofool on September 12, 2020, 10:11:18 pm: My reply above is incorrect for the V6 engine. I was thinking of the L4. Sorry.

The coolant temperature sensor is in the outflow path of the cooling system. It's in the lower manifold which is receiving water direct from the cooling jacket around the cylinders and in the heads. The coolant passes over the CTS and exits up through the thermostat housing. The gauge sending unit is in the flow as coolant comes up from the block on it's path through the head and into the lower intake. Probably because the flow is so fast, the temperatures are equal.
Title: Re: Overheat?
Post by: GTRS Fiero on September 13, 2020, 04:06:28 am: Therein lays the problem. My temperatures aren't equal, which probably means that the flow is not fast.
Title: Re: Overheat?
Post by: Fierofool on September 13, 2020, 07:21:15 am: Probably because the flow is so fast, the temperatures are equal. That was my theory. The fan switch is set in the intake also and it may not come on at the prescribed temperature when compared to the other two temp sensors. They aren't precise instruments and they can be made by a wide variety of different manufacturers. Because of it's proximity to the combution chamber, I could see the gauge sending unit reading or displaying a higher temperature.
Title: Re: Overheat?
Post by: GTRS Fiero on September 13, 2020, 07:05:02 pm: Still need to know if it actually overheats.
Title: Re: Overheat?
Post by: TopNotch on September 13, 2020, 08:25:16 pm: Quote from: GTRS Fiero on September 13, 2020, 07:05:02 pm
Still need to know if it actually overheats.
Does it ever boil over, or dump an excess amount of coolant into the overflow bottle? That's one sign of overheating.
Another, if it's due to air pockets, is a popping noise while the temp is high.
Title: Re: Overheat?
Post by: GTRS Fiero on September 13, 2020, 08:34:06 pm: Neither of those things.
Title: Re: Overheat?
Post by: Fierofool on September 13, 2020, 08:47:06 pm: Is your ECM programmed to control the coolant fan or does it still operate off the fan switch? If off the ECM, what is the upper and lower settings? If off the switch, what is the on and off for the switch.

Knowing these values, you can let the car sit and idle after a warm up drive, and see if the fan comes on at a gauge temperature that agrees with your controlling device.
Title: Re: Overheat?
Post by: GTRS Fiero on September 13, 2020, 08:55:35 pm: By the ECU. I don't recall the set temps, but they are set for a 180-degree thermostat. I did the idle test. The fan comes on when the CTS (via the ECU) hits about 190. The gauge shows whatever. It sometimes agrees with the CTS.
Title: Re: Overheat?
Post by: GTRS Fiero on September 24, 2020, 06:27:34 pm: There appears to be a short. Does anyone know the physical path for this wiring?
Title: Re: Overheat?
Post by: GTRS Fiero on September 26, 2020, 01:55:57 pm: The gauge needle can move half an inch at a time, up or down. There must be something happening. The gauge readings are now much worse. The gauge indicates past the red very often, now. In fact, the gauge almost always shows overheating.
Title: Re: Overheat?
Post by: TopNotch on September 27, 2020, 04:37:30 pm: Could be bad wiring somewhere. Since the temp gauge is a resistance operated device, any additional resistance in the circuit, such as caused by a bad connection somewhere, will throw it off.
Title: Re: Overheat?
Post by: GTRS Fiero on September 27, 2020, 04:39:57 pm: In this case, less resistsnce. To me, that means a short. My theory is bad wiring, since it got worse after the temp gauge pigtail was replaced. It almost seems to be right there in that harness.
Title: Re: Overheat?
Post by: GTRS Fiero on October 03, 2020, 04:47:27 pm: My Fiero is not overheating. That hsving been stated, last night, I drove 238 miles on the first tank, with the temp gauge a bit higher than the black mark above the red. Rometimes, the needle would move as much as half an inch higher than that. 8.39 gallons of gas.

I drove 254 miles on the next tank, and the needle stayed mostly below the red. 8.03 gallons of gas.

Running 80 MPH does not improve fuel economy.

Frustrating.
Title: Re: Overheat?
Post by: Roger on October 10, 2020, 05:58:06 pm: Try this:

I tried to get the right file posted but now I can't see my own post. PITA!
Title: Re: Overheat?
Post by: GTRS Fiero on October 13, 2020, 07:31:39 pm: I'm fairly sure this is too hot.
Title: Re: Overheat?
Post by: GTRS Fiero on November 16, 2020, 10:46:09 pm: Got a lot of the wiring harness apart. No apparent issues. Still trying to figure out the cruise control. Also looking for this overheating issue.
Title: Re: Overheat?
Post by: HarryT on November 17, 2020, 02:19:59 am: 87 MPH at 2350 RPM?
Harry
Title: Re: Overheat?
Post by: GTRS Fiero on November 17, 2020, 06:05:45 am: That does not cause overheating. I do need to see why the TCC isn't locking, though.
Title: Re: Overheat?
Post by: Fierofool on November 17, 2020, 08:25:50 am: If the converter isn't locking and a HarryT observed, you are only turning 2350 at 87MPH, you should be realizing about 60 MPG.

If your temperature is really that high, then your engine would likely shut down n short order. Test your leads at the sending unit, again. Determine which one causes the Temperature light to display. Then, with the engine cold, do a continuity test on the terminals of the sending unit. At temperatures below operating temperature, there will be no resistance when probed between the light terminal and the sensor base as that switch is open. The gauge side will show resistance. Be sure your leads are connected to the correct terminals. They can easily be repinned in the harness connector if they have been switched.

If everything is correct, then you have either wiring or gauge problems.
Title: Re: Overheat?
Post by: GTRS Fiero on November 17, 2020, 06:58:33 pm: Well, my Fiero does not shift to 4th until about 60 MPH. Below that, my MPG is not that great. Maybe due to the thermostat, it's running rich. With the EGR/vacuum leak, MPG decreases. My Fiero was getting 35 MPG, combined, last year. The bad pushrod probably did not help. The picture was not edited, and the gauges were calibrated correctly.
Title: Re: Overheat?
Post by: GTRS Fiero on November 18, 2020, 07:00:48 pm: Replacing the calibrated gauge made things...better. this gauge is not calibrated, and sometimes decides to read hot.

The wiring from the temp gauge sender to the firewall has all been tested. The wiring in the dash was gone through. There may be a bad connection where the plugs connect to the instrument panel. When the gauge reads hot, turning the key off aand on 3 times gets the gauge reading below the red again. If sitting with the engine off, key on, sometimes the gauge just decides it's time to read hot. The gauge reads correctly when off, but seems to read about 80 degrees hot when on.
Title: Re: Overheat?
Post by: GTRS Fiero on November 27, 2020, 12:44:23 pm: I was told that the thermostat is always open, once the engine warms up. That does not make sense to me. It would seem that the thermostat would continue to open and close, to regulate the temperature of the coolant. Which is correct?
Title: Re: Overheat?
Post by: Fierofool on November 27, 2020, 03:34:23 pm: Once the coolant reaches the thermostat temp rating it stays open. It might partially close if temp drops appreciably. Just a guess, but I know it stays open at or above temp rating.
Title: Re: Overheat?
Post by: GTRS Fiero on November 27, 2020, 03:37:27 pm: If it stays open, how could removing the thermostat affect MPG? The engine warms up quickly, so it would only make a difference on warm-up.
Title: Re: Overheat?
Post by: scottb on November 27, 2020, 03:49:51 pm: If you take out the thermostat the engine won't get to operating temp and will run rich destroying your fuel economy
Title: Re: Overheat?
Post by: Fierofool on November 27, 2020, 08:00:02 pm: There is also some restriction with the thermostat in place. With it removed, that restriction is removed and the coolant flows freer, with the result Scott described.
Title: Re: Overheat?
Post by: GTRS Fiero on November 27, 2020, 08:07:45 pm: I may change back to the 195 thermostat.
Title: Re: Overheat?
Post by: GTRS Fiero on February 14, 2021, 10:19:49 am: A new thermostat did not fix the problem. Recalibrating the gauges yielded no changes. Ran a temporary wire from the temp sender to the gauge. No change. For thoroughness, tested resistance from the pin on the tem sender to the gauge: .4 Ohms.

Replaced the temp sender, again, because the sender was reading all over the place.
Title: Re: Overheat?
Post by: GTRS Fiero on February 14, 2021, 06:29:48 pm: Quote from: Fierofool on November 27, 2020, 03:34:23 pm
Once the coolant reaches the thermostat temp rating it stays open. It might partially close if temp drops appreciably. Just a guess, but I know it stays open at or above temp rating.

Watching my temp on multiple vehicles, the needle moves--more dramatically on some vehicles than on other vehicles. Usually, this is caused by the opening and closing of the thermostat. Discussing this with a mechanic, the thermostat does open and close to allow the coolant from the radiator to be regulated. Unfortunately, the regulation occurs after potentially cold coolant has already been drawn into a hot engine. The thermostat does not know if the engine is running or not--only the coolant temp.

When the temps were -20 or so, we used to put cardboard in front of the grille, so we would have heat. The engine temp was usually OK.
Title: Re: Overheat?
Post by: GTRS Fiero on February 21, 2021, 06:04:00 pm: The problem was a bad temp sender. Lots and lots of bad temp senders. Made in china.
Title: Re: Overheat?
Post by: GTRS Fiero on March 09, 2021, 07:24:59 pm: The temp on the gauge now shows just below 220, or about there. The fan comes on, but all good.
Title: Re: Overheat?
Post by: GTRS Fiero on May 21, 2021, 07:25:29 pm: That didn't last long. The only thing I can figure is the water pump. Again. The coolant does circulate, but sometimes the engine gets too warm.