Troubleshooting car underheating

[KK]

I got a 94 ford ranger that is not warming up to its normal operating tempature. The temperature guage comes up alittle bit but not near where it used to. Today I changed the thermostat thinking it was stuck open. THis did not change the situation. The heat blows warm air, just not hot like it used to. So I don't think the actual guage is screwed up since the heat blowing seems to be about what it should be given the reading on the guage. Any ideas on how to raise the temp besides placing cardboard infront of the radiator?

 

[Shawn]

How cold is it outside?

 

[mobobuff]

Originally posted by: Shawn
How cold is it outside?

He lives in Georgia, it can't be THAT cold.

43 degrees. Still not that cold.

 

[KK]

lately its been in the between 30-50 something. doesn't seem to be affected too much by the outside temp.

 

[SlitheryDee]

A lower than usual temperature gauge reading and less than hot air could mean that your car is simply low on coolant. The thermostat depends on water flowing through it to get an accurate measurement and if there's no hot water (or water period) to flow through the heating coils then your heater won't blow hot air.

My car did the same thing before blowing a head gasket due to overheating. I'd definitely check coolant levels if I were you as it is a VERY bad thing to drive a vehicle with little or no coolant.

 

[oynaz]

A car engine runs with very high temperatures, so the outside temperature does not have any influence. I have seen a car with a defective cooler overheat in -35 degrees Celcius (-31 degress F).

Btw, Most likely your cooler is defective somehow. I would start with checking that.

 

[mobobuff]

Originally posted by: SlitheryDee
A lower than usual temperature gauge reading and less than hot air could mean that your car is simply low on coolant. The thermostat depends on water flowing through it to get an accurate measurement and if there's no hot water (or water period) to flow through the heating coils then your heater won't blow hot air.

My car did the same thing before blowing a head gasket due to overheating. I'd definitely check coolant levels regularly if I were you.

Sounds reasonable to me.

 

[Squisher]

Originally posted by: SlitheryDee
A lower than usual temperature gauge reading and less than hot air could mean that your car is simply low on coolant. The thermostat depends on water flowing through it to get an accurate measurement and if there's no hot water (or water period) to flow through the heating coils then your heater won't blow hot air.

My car did the same thing before blowing a head gasket due to overheating. I'd definitely check coolant levels if I were you as it is a VERY bad thing to drive a vehicle with little or no coolant.

If he changed the thermostat, chances are he topped off the coolant.

 

[KK]

Originally posted by: SlitheryDee
A lower than usual temperature gauge reading and less than hot air could mean that your car is simply low on coolant. The thermostat depends on water flowing through it to get an accurate measurement and if there's no hot water (or water period) to flow through the heating coils then your heater won't blow hot air.

My car did the same thing before blowing a head gasket due to overheating. I'd definitely check coolant levels if I were you as it is a VERY bad thing to drive a vehicle with little or no coolant.

Well, we did flush out the radiator when we changed the thermostat, and filled it back up. Back when I first noticed the problem the reservoir was bone dry because my dumbass forgot to put the cap on the reservior. I thought back then, that once I filled that reservoir up that the temps would come back up to normal. ran it for a few weeks and no change, the levels in the reservior stayed constant.

 

[Black88GTA]

Maybe a plugged / bad heater core?

EDIT: Nvm, if the gauge isn't coming up to normal levels, then this wouldn't make sense. There's something else going on. I would guess thermostat...maybe your new one is defective?

 

[KK]

Originally posted by: oynaz
A car engine runs with very high temperatures, so the outside temperature does not have any influence. I have seen a car with a defective cooler overheat in -35 degrees Celcius (-31 degress F).

Btw, Most likely your cooler is defective somehow. I would start with checking that.

when you say cooler, what parts are you referring to?

 

[SlitheryDee]

Originally posted by: KK

Originally posted by: SlitheryDee
A lower than usual temperature gauge reading and less than hot air could mean that your car is simply low on coolant. The thermostat depends on water flowing through it to get an accurate measurement and if there's no hot water (or water period) to flow through the heating coils then your heater won't blow hot air.

My car did the same thing before blowing a head gasket due to overheating. I'd definitely check coolant levels if I were you as it is a VERY bad thing to drive a vehicle with little or no coolant.

Well, we did flush out the radiator when we changed the thermostat, and filled it back up. Back when I first noticed the problem the reservoir was bone dry because my dumbass forgot to put the cap on the reservior. I thought back then, that once I filled that reservoir up that the temps would come back up to normal. ran it for a few weeks and no change, the levels in the reservior stayed constant.

Well that's out then...I'm stumped.

 

[KK]

would the temperature sensor be on the output or input of the heater core. there is an electronic sensor that is on the smaller hose coming out of the thermostat, which I would think would going to the heater core. Now if the antifreeze isnt circulating thru the heater core very good would that give me the same indications I'm getting?

 

[BUTCH1]

What's the milage on the truck?? Maybe the water pump vanes are worn badly or calcified.
causing poor coolant flow..

 

[compuwiz1]

Bad guage
Bad temp sending unit
Bad thermostadt

Gotta be one of the three, IMO.

If not one of them, then maybe you have an obstruction in the heating circuit.

 

[Black88GTA]

Originally posted by: compuwiz1
Bad guage
Bad temp sending unit
Bad thermostadt

Gotta be one of the three, IMO.

If not one of them, then maybe you have an obstruction in the heating circuit.

If it were a bad gauge or temp sending unit, then the heat would work fine, regardless of gauge reading. Unless there's more than one problem (i.e. bad heater core + bad sender / gauge) - except this is unlikely, since (from the post) it seems that both things started happening at the same time.

If the WP wasn't working properly, I would think that the car would overheat, rather than run cold...

It could still be a heater core - if the temp gauge sender is located somewhere in that circuit. Although I don't think they are in most cars.

OP, you should probably try to determine the location of the temp sender - look online or find a service manual somewhere. If it is in the lines leading to / from the HC, then the core could be the problem.

Alternatively, you could maybe try finding where the hoses enter the firewall for the heater core, and "jump" the two together with a piece of copper pipe and some hose clamps. If the gauge has no reading, or returns to normal operation, then there's likely something wrong with the HC.

 

[KK]

Originally posted by: BUTCH1
What's the milage on the truck?? Maybe the water pump vanes are worn badly or calcified.
causing poor coolant flow..

around 133,300

Originally posted by: compuwiz1
Bad guage
Bad temp sending unit
Bad thermostadt

Gotta be one of the three, IMO.

If not one of them, then maybe you have an obstruction in the heating circuit.

If it was a bad guage or something regarding the guage I would believe my hot air would still be coming out from the heater. Thermostat has been changed today, whats the chance that the new one is also bad.

 

[KK]

Originally posted by: Black88GTA

Originally posted by: compuwiz1
Bad guage
Bad temp sending unit
Bad thermostadt

Gotta be one of the three, IMO.

If not one of them, then maybe you have an obstruction in the heating circuit.

If it were a bad gauge or temp sending unit, then the heat would work fine, regardless of gauge reading. Unless there's more than one problem (i.e. bad heater core + bad sender / gauge) - except this is unlikely, since (from the post) it seems that both things started happening at the same time.

If the WP wasn't working properly, I would think that the car would overheat, rather than run cold...

It could still be a heater core - if the temp gauge sender is located somewhere in that circuit. Although I don't think they are in most cars.

OP, you should probably try to determine the location of the temp sender - look online or find a service manual somewhere. If it is in the lines leading to / from the HC, then the core could be the problem.

Alternatively, you could maybe try finding where the hoses enter the firewall for the heater core, and "jump" the two together with a piece of copper pipe and some hose clamps. If the gauge has no reading, or returns to normal operation, then there's likely something wrong with the HC.

on the thermostat housing it had the larger tuble going to the radiator and a smaller hose that went back around the engine to the firewall, and on the path going back was the only electronical part I seen that was on the hose. ALthough I didn't really examine once I seen that electronic part, thinking that was the sensor.

 

[Squisher]

Originally posted by: KK
on the thermostat housing it had the larger tuble going to the radiator and a smaller hose that went back around the engine to the firewall, and on the path going back was the only electronical part I seen that was on the hose. ALthough I didn't really examine once I seen that electronic part, thinking that was the sensor.

If there is a blockage in the heater core and the temp sensor is in that pathway then it could be the cause of the problem.

Do you see the temp rise on the gauge then fall back maybe 5% (when the thermostat opens)?
Do you see the coolant sitting in the radiator then after idling ten minutes start to move and get hot? A thermometer dipped down into the radiator would help to confirm the performance of the thermostat.

 

[drum]

I have a 94 ranger with 133k miles too :shocked:
I was going to say thermostat or coolant problem but you've obviously eliminated that.
I had trouble with overheating last summer and put an aftermarket radiator in which fixed it, but your problem is obviously opposite.
do you have the 3 or 4 litre?

 

[KK]

Originally posted by: Squisher

Originally posted by: KK
on the thermostat housing it had the larger tuble going to the radiator and a smaller hose that went back around the engine to the firewall, and on the path going back was the only electronical part I seen that was on the hose. ALthough I didn't really examine once I seen that electronic part, thinking that was the sensor.

If there is a blockage in the heater core and the temp sensor is in that pathway then it could be the cause of the problem.

Do you see the temp rise on the gauge then fall back maybe 5% (when the thermostat opens)?
Do you see the coolant sitting in the radiator then after idling ten minutes start to move and get hot? A thermometer dipped down into the radiator would help to confirm the performance of the thermostat.

Yes the guage fluctuates alittle. I'm guessing the thermostat opening and closing is causing that. Prior to changing the thermostat I thought maybe the fluctuation was due to stopping and starting thus causing more or less air to cool off the radiator. But since replacing the thermostat and it doing the smae, its probably opening and closing ok.
Tonight when I head home, I'll run over to my fathers and will take a temperature reading. I'm guessing a cooking thermometer will work.

 

[KK]

Originally posted by: drum
I have a 94 ranger with 133k miles too :shocked:
I was going to say thermostat or coolant problem but you've obviously eliminated that.
I had trouble with overheating last summer and put an aftermarket radiator in which fixed it, but your problem is obviously opposite.
do you have the 3 or 4 litre?

3 or 4 litre, I wish. 2.3L

 

[Black88GTA]

Originally posted by: KK

Originally posted by: drum
I have a 94 ranger with 133k miles too :shocked:
I was going to say thermostat or coolant problem but you've obviously eliminated that.
I had trouble with overheating last summer and put an aftermarket radiator in which fixed it, but your problem is obviously opposite.
do you have the 3 or 4 litre?

3 or 4 litre, I wish. 2.3L

My 92 Mustang had the same motor, and oddly enough, the exact same problem as yours - temp gauge staying much lower than normal, very little heat. The cause of mine was very obvious when I opened the thermostat housing...the thermostat had split and was in a number of pieces, causing unchecked flow of coolant and not allowing it to reach proper operating temp. That's why I originally thought it was the thermostat (I'm still not 100% convinced that's not it )

 

[funboy6942]

Im guessing since you replaced your thermo, and assuming fluids are topped off that it is one of 2 things.

Electric fan is on all the time if so equipped or clutch on bolted on fan is not operating properly and it sucking it too much air through the radiator cooling it off to much.

If electric just start the truck and if the fan is on all the time, well there you go, it shouldn't, it needs to only come on once and a while.

If a bolted on fan to the engine when you start the truck is it really loud and making a loud whooshing sound all the time when you give it gas, if so the fluid in the clutch is worn out and the clutch is not letting the fan "relax" and the whooshing sound is it really sucking the air through the radiator. These are the only two things that would come to mind since your saying your temp gage isnt reading in the norm like it used to and the heat coming out isn't as hot, meaning the coolant is getting cooled off too much and only thing going to do that is the fan and air passing through it since its really not sub zero out where your at.

 

[jupiter57]

Originally posted by: KK

Originally posted by: BUTCH1
What's the milage on the truck?? Maybe the water pump vanes are worn badly or calcified.
causing poor coolant flow..

around 133,300

Originally posted by: compuwiz1
Bad guage
Bad temp sending unit
Bad thermostadt

Gotta be one of the three, IMO.

If not one of them, then maybe you have an obstruction in the heating circuit.

If it was a bad guage or something regarding the guage I would believe my hot air would still be coming out from the heater. Thermostat has been changed today, whats the chance that the new one is also bad.

From over40 years experience as a shade tree mechanic, I can say with no uncertainty that the chances of the new thermostat being bad is 50%.
I always buy 2 at a time, no more than they cost, and saves me a trip to town if the first is bad.
Some years back, I got 3 in a row (On the same day, for the same car) from AutoZone that were faulty, what a nightmare!