Temp Gauge Fluctuation & Heat Issue

boodaddy · #1 11-21-2012, 05:10 PM

Hello,

A couple days ago my temp gauge started fluctuating. It wold go to normal temp, and then it would drop to cool. At a stop light it would go normal and then drop again. At the same time this happened the heat went out, and blew just a little heat mixed with cool air.

The computer said that the AC sensors was stuck open so I replaced both of those, and replaced the temp gauge sensor not the computer temp sensor. The gauge is still fluctuating, and heat was the same.

I unplugged the AC from the compressor and the heat is blowing fine. At least I have heat for now.

What would cause both of these to act like this all of a sudden? I am going to order a used HVAC control panel off Ebay for cheap troubleshooting. I am hoping that it is not the blend door/ actuator, but the gauge acting up at the same time doesn't make sense.

Appreciate any help or advice you can offer.

FireRanger · #2 11-21-2012, 05:57 PM

The AC is not plugged into the alternator. You're confused about what you're unplugging and testing for.

Please stop blindly replacing parts. IDK why you replaced the temp sensor when it was obviously working fine. It was indicating low when the heat stopped and normal when the heat was working.

Run through the troubleshooting guide to see where it leads you. It is obviously not the blend door and and not the HVAC control panel. Those thing don't change the temperature of your coolant. It's either a water pump going bad, or a thermostat sticking open, or low coolant. Since you haven't said what kind of engine you have, I can't go any further.

boodaddy · #3 11-21-2012, 08:24 PM

Quote:

Originally Posted by FireRanger

The AC is not plugged into the alternator. You're confused about what you're unplugging and testing for.

Please stop blindly replacing parts. IDK why you replaced the temp sensor when it was obviously working fine. It was indicating low when the heat stopped and normal when the heat was working.

Run through the troubleshooting guide to see where it leads you. It is obviously not the blend door and and not the HVAC control panel. Those thing don't change the temperature of your coolant. It's either a water pump going bad, or a thermostat sticking open, or low coolant. Since you haven't said what kind of engine you have, I can't go any further.

I meant I unplugged the AC Compressor. I had Alternator on my mind. My bad. I edited. I wasn't trying to blindly replace parts. Stuck open AC sensors will keep kicking the fan on which was happening to me a lot.

I don't understand how the sensor wouldn't be bad when It would go all the way down to cool and back up again just at a stop light. Heat or no heat, so I replaced a $10.00 part just to make sure.

I just had a coolant flush and it's still doing the same thing. I have a 2.5L L4 SOHC 8V engine.

FireRanger · #4 11-21-2012, 08:58 PM

If the heater was staying hot, then I would suspect the temp sensor. But if the heater is not staying hot and the sensor is also reading up and down, then obviously the sensor is working fine. And the AC system has nothing to do with the heat working or not.

It's probably your water pump failing or stuck thermostat. Or both.

jarrod27 · #5 11-21-2012, 09:06 PM

Sounds to me your thermostat is failing, because when they fail they usually stick open sometimes. If you replace it use a motor craft one. You might have air in the cooling system also, it will cause the gauge to fluctuate. I use a u view coolant tool to fill coolant systems.

boodaddy · #6 11-21-2012, 09:41 PM

Quote:

Originally Posted by FireRanger

If the heater was staying hot, then I would suspect the temp sensor. But if the heater is not staying hot and the sensor is also reading up and down, then obviously the sensor is working fine. And the AC system has nothing to do with the heat working or not.

It's probably your water pump failing or stuck thermostat. Or both.

The temp sensor is stuck on cold now. Because I just replaced it, I think it might be the thermostat because when it got stuck on cold the heat quit working.

Before the only way the heat would work is when the compressor was unplugged. Plugged it back in, and it was cool. I was thinking this was because of a stuck blend door. I don't know much, but that did make the heat work again. I am going to replace the thermostat and see if that does the trick because the the gauge went to cold and wont move now.

jarrod27 · #7 11-21-2012, 10:06 PM

Quote:

Originally Posted by boodaddy

The temp sensor is stuck on cold now. Because I just replaced it, I think it might be the thermostat because when it got stuck on cold the heat quit working.

Before the only way the heat would work is when the compressor was unplugged. Plugged it back in, and it was cool. I was thinking this was because of a stuck blend door. I don't know much, but that did make the heat work again. I am going to replace the thermostat and see if that does the trick because the the gauge went to cold and wont move now.

Your blend door is broke. The compressor will be not be activated if the mode switch is on the (vent only or floor only) position, but if it's in any of the other positions defrost/floor vent mix/ ac/ ac max the ac clutch will engage. Since the door is broke the cold air from the evaperator is coming in with the heater core air.

FireRanger · #8 11-22-2012, 09:17 AM

Again since the AC has absolutely nothing to do with anything....

Quote:

Originally Posted by FireRanger

It's probably your water pump failing or stuck thermostat. Or both.

jarrod27 · #9 11-22-2012, 09:36 AM

Well if your suspecting that his thermostat is faulty, like I did tell him how to test it without live data from a scan tool. Go out and feel the upper radiator hose if it feels cool and the gauge is low then it's sticking open. If your pump is bad you can hear it make noise, you can also pull the belt and spin the pump and listen for bad bearings inside it, if the shaft moves in any direction it's bad also there is a small hole in the case if there is any coolant coming out the wheel hole it's bad.

FireRanger · #10 11-22-2012, 10:35 AM

The pump failing causing a lack of coolant flow wouldn't have anything to do with the bearings or weep hole. It's the impeller rotting out. All the steps for checking one or the other are in my guide so I'm not retyping it all again.

boodaddy · #11 11-22-2012, 02:21 PM

Quote:

Originally Posted by jarrod27

Well if your suspecting that his thermostat is faulty, like I did tell him how to test it without live data from a scan tool. Go out and feel the upper radiator hose if it feels cool and the gauge is low then it's sticking open. If your pump is bad you can hear it make noise, you can also pull the belt and spin the pump and listen for bad bearings inside it, if the shaft moves in any direction it's bad also there is a small hole in the case if there is any coolant coming out the wheel hole it's bad.

Went outside let it run for 15 min and temp guage didn't hardly move at all from cold. Felt the upper radiator hose and its cold. The temp guage would move a little when I raised the rpms a little then back down. I'm going to replace the thermostat.

jarrod27 · #12 11-22-2012, 03:48 PM

If the impeller was rotted out then his engine would get hot not cold due to no coolant flow.

FireRanger · #13 11-22-2012, 04:04 PM

On the 4 cylinders, the sensor and the heater core are on the same line. They are the highest and farthest places for water to be pumped. When the impeller is starting to rot out, the heater core and sensor lose circulation first. While still maintaining enough circulation to the rest of the block to not overheat. Fluctuations in flow and temperature is a common sign of this.

This is detailed in the troubleshooting guide. With pictures.

So his problem could be either or both.

boodaddy · #14 11-23-2012, 12:15 AM

Quote:

Originally Posted by jarrod27

If the impeller was rotted out then his engine would get hot not cold due to no coolant flow.

Quote:

Originally Posted by FireRanger

On the 4 cylinders, the sensor and the heater core are on the same line. They are the highest and farthest places for water to be pumped. When the impeller is starting to rot out, the heater core and sensor lose circulation first. While still maintaining enough circulation to the rest of the block to not overheat. Fluctuations in flow and temperature is a common sign of this.

This is detailed in the troubleshooting guide. With pictures.

So his problem could be either or both.

I am praying it is the thermostat. I am going to get the parts tomorrow, so I'll keep ya posted. Appreciate your time, help and advice.

jarrod27 · #15 11-24-2012, 06:32 PM

Just as a heads up, you might Want to buy the motor craft thermostat. The after market on doesn't stay in the housing when your installing it, but the motorcraft one does. O'Reilly can get it.