Engine Coolant Temperature (ECT) Sensor

[ktdenali]

When I first started my Subaru (2000, manual,Outback LTD) this morning the engine cooling fans came on right away. In fact I noticed they come on at the oddest times.

The Head Gaskets have just been replaced, so the thermostat is new, my coolant is new, and all that goes with it.

 

I am wondering if my ECT sensor is bad. I have had that problem on a different Subaru before, but that one would also have a rough start. The engine would shake unbalanced and the the fans would come on at -20 F, on cold start. Replacing the ECT fixed that.

 

On this one I just noticed the fans coming on at some odd times (like first start in real cold) and also lately I had a small leak of coolant somewhere. Can't find it, and it's kind of gone now.

 

Mechanics! Any input? Please...

[ktdenali]

Just from reading some posts... I forgot to look if my defrost was on at first starting up. I did not think that would turn my engine cooling fans on.

 

Also if the ECT sensor was bad, wouldn't that trigger the "Check Engine" light??

[OB99W]

[...]Also if the ECT sensor was bad, wouldn't that trigger the "Check Engine" light??

No, that won't trigger a CEL -- the ECU doesn't know it's being "lied to".

[1-3-2-4]

defrost can turn the fans on.. having the A/C button pressed will turn the fans on..

 

report back when you check.. it would be better to hook a live scanner up and see what the ECT is showing a reading of after sitting over 24 Hr.. lol if it's maxed out at over 220 F when it's 32F outside then you have a problem

[MilesFox]

Since you mentioned headgaskets, I would assume you had an overheat. An overheat may have stretched ther sensor to where it does not read accuately.

 

I have had the cheap mechanical water temp gauges and overheated. After the overheat, the gauge would read high.

 

The same could be true with your sensor, that it may be 'stretched out'. If the fans come on right away, the sensor may be telling the computer the car is warm all the time.

[ktdenali]

After a couple of days of using and watching it, I am pretty sure it was just my defrost left on. Now I pay attention and turn it off when I park the car. So the fans have not come on at all on cold engine.

 

No, I did not have an overheat. As far as I know, which is little, not all head gasket problems end up in overheat (some internal, some external leaks.) I caught my HG problem because I had bubbles in my overflow tank. Combustion fumes in the cooling system.

 

What you say makes sense though. If there is an overheat, it makes sense to replace all temperature gunge parts, 'cause they will be inaccurate.

 

Thanks!

[ktdenali]

Also!

 

On a previous Subaru ('96 legacy, manual), I had a bad ECT sensor.

Symptoms:

It was not only the fans came on at the wrong times, but also it would have the hardest time starting. Unless it was butt freezing cold outside, then it fired right up.

In less cold weather, the engine would shake, like imbalanced, kind of like if a piston was not firing or something.

 

That is another reason I am now convinced I had no problem with ECT sensor in his Subi because it was only fans messing me up, no other signs.