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Temperature gauge reading low

B

Bugly

New CEG'er
Joined
Jun 11, 2008
Messages
14
Location
North East Pa.
Hello all,
I've been searching for a while and can now post. I have a 1997 Mercury Mystique 2.0 zetec engine with the following question... I am in the process of changing the antifreeze and thermostat since the temp gauge is reading low...barely moving and not even getting near the N. While flushing the system I noticed that the cooling fan did not go on. I unplugged the connector to the switch located on the thermostat housing and the fan went on. Plugged it back in and the fan stopped. I assume that this is the fan switch and has to be replaced. Am I correct here? I also assume that the coolant temp senor controls the gauge but I cant find it. Can anyone help me as to where I may locate this. I have read that this is a common problem but want to get it close to right.

Thanks again for any help..

Kevin
 
Bugly said:
While flushing the system I noticed that the cooling fan did not go on. I unplugged the connector to the switch located on the thermostat housing and the fan went on. Plugged it back in and the fan stopped. I assume that this is the fan switch and has to be replaced. Am I correct here?
Click to expand...

The low speed for the Zetec cooling fan does not go on until around the "L" in "NORMAL" when all aspects are working correct... When you unplug that connector, it automatically goes on because the PCM is getting no signal as to how hot the coolant is...

Bugly said:
I also assume that the coolant temp senor controls the gauge but I cant find it. Can anyone help me as to where I may locate this. I have read that this is a common problem but want to get it close to right.
Click to expand...

It is located on the underside of the thermostat housing...

----------

Also, you may want to look into changing the actual themostat, it could be stuck open not allowing the car to heat up...
 
As already stated, the reason the fan comes ON when unplugged is that the PCM is assuming the temp is pegged, since there is no signal for temp.

this means that the sensor likely works.

the abnormally cool condition could be caused by an open thermostat, a stuck fan relay (which you say you don't have a fan running, so....) or abnormally cool temperatures in the weather.

I think BoSoxBruin is dead on with the probable cause. I'd look at changing the thermostat, and go from there. If you still don't have a change, your temp sender for the gauge (which is separate from the temp sensor for the PCM to control the fans) may be out of range causing the NEEDLE to stay low regardless of actual coolant temps. You may be perfectly warmed up, just not knowing it based on a faulty needle position, due to a stuck needle or faulty sender.
 
Thanks for the quick reply BoSoxBruin...I forgot to mention that I did swap out the stat with a new one...My first thought as to why it always read cool. When I flushed the system I ran the air conditioning and defroster on high. Should the fan have been on then? In reference to the coolant sensor under the housing...How do you get to it? Do you have to remove the coil pack..or do you have to take the the housing off? Thanks again for the quick response.That petcock was a BEAR to get off.

Kevin
 
Bugly said:
When I flushed the system I ran the air conditioning and defroster on high. Should the fan have been on then?
Click to expand...

Yes, I forgot to post that, the fan should be on at all times with the A/C on...

Bugly said:
That petcock was a BEAR to get off.
Click to expand...

I had the same opinion, then I was told on here that was the hard way to drain the system... On the underside of the car on the passenger side behind the engine there should be a rubber coolant hose which changes into a metal hose... You can just undo that to drain the system...
 
Thanks again for the quick reply...since the fan never went on even when the ac and defroster were on..which way do I go? as far as the stat..it is new but is there a way to check it?.. thanks for the coolant drain tip..in case I have to do it again..

Kevin
 
Bugly said:
....as far as the stat..it is new but is there a way to check it?.. ....Kevin
Click to expand...

1) Get an Infra Red Thermometer (about $50 from auto stores). Read temps before and after thermostat. It should be same (hot) after the car warms up. If there is a great differential, the thermostat is not opening.

or

2) Remove it and put it in boiling water with a thermometer. It should open at 195 degrees or so.
 
Last edited:
To bring this topic up again, I have a 98 Contour GL 2.0l 4 and it has always run cool. The temp guage barely leaves the gap between the white block and the "N" in Normal. I figured the thermostat was stuck open, so I just replaced it while changing the coolant. Ran it up and down the road to warm it up while doing a flush with straight water, and it still doesn't register any higher than before. I have to re-drain the system tomorrow and put in 50/50, but should I be concerned about it running cool, or just registering cool? The engine seems to get plenty warm, and I ran the heater on HIGH and hot to flush the heater core while I was changing the coolant and lemme tell you, it got pretty darn warm inside the cabin. The coolant temperature sensor is the one right on top of the thermostat housing?

ETA: Would it be the engine coolant temperature SENDER, or the engine coolant temperature SENSOR, as I guess these are separate and distinct units?
 
Scorpion8 said:
To bring this topic up again, I have a 98 Contour GL 2.0l 4 and it has always run cool. The temp guage barely leaves the gap between the white block and the "N" in Normal. I figured the thermostat was stuck open, so I just replaced it while changing the coolant. Ran it up and down the road to warm it up while doing a flush with straight water, and it still doesn't register any higher than before. I have to re-drain the system tomorrow and put in 50/50, but should I be concerned about it running cool, or just registering cool? The engine seems to get plenty warm, and I ran the heater on HIGH and hot to flush the heater core while I was changing the coolant and lemme tell you, it got pretty darn warm inside the cabin. The coolant temperature sensor is the one right on top of the thermostat housing?

ETA: Would it be the engine coolant temperature SENDER, or the engine coolant temperature SENSOR, as I guess these are separate and distinct units?
Click to expand...

Coolant Temperature Gauge SENDER. This is the one which could be the problem.
 
Re-flushed my cooling system and filled it with NAPA 50/50 coolant. Ran it up and down the highway and it still reads a very low temperature. I even took the coolant temp sender out and used a green scratch pad to clean it up a bit. Sender unit = bad?
 
Scorpion8 said:
Re-flushed my cooling system and filled it with NAPA 50/50 coolant. Ran it up and down the highway and it still reads a very low temperature. I even took the coolant temp sender out and used a green scratch pad to clean it up a bit. Sender unit = bad?
Click to expand...

The SENDER unit is the one on the bottom of the thermostat housing, just to make sure that is the one you took out...
 
BoSoxBruin said:
The SENDER unit is the one on the bottom of the thermostat housing, just to make sure that is the one you took out...
Click to expand...

Ah, must be the reason. I pulled the one on TOP of the thermostat housing in order to let the cooling system air escape while I was filling it with new antifreeze/coolant. I hadn't noticed the one underneath. I'll procure a new SENDER and replace that.
 
Me thinks I have an intermitten connection possibly. Was driving home from work today and the temp gauge went all the way to just shy of the middle (about where it should be). Either the connection is intermittent, or the sender is. I'll still get a new sender, and check the wiring connector for frays and shorts too.
 
Argh! I was in Anchorage yesterday, and went to three Schucks's Auto and the big Ford dealer and no one carries the sender unit. They all have the sensor, and in fact most of them couldn't even find the sender unit in their parts books or computer. What good is a Ford dealer if they don't carry parts?!

Oh, and I had bought a new Craftsman 16mm combination wrench for my tool box. Just a single wrench. TSA confiscated it at the airport. What, did they think I might fix the plane or hijaack it to Havana with a single wrench?
 
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