Ford Focus 1.6 2004 - ECT sensor position and function #
Posted by Steve Nicholas on October 27, 2012, 6:13 pm
Year of Manufacture *: 2004 Engine Size and Code *: 1.6 Zetec
Hi
Just a query for confirmation on how these systems are designed to sense coolant temperature using the Cylinder Head Temperature (CHT) sensor alone.
Using Solus Ultra to collect serial data I was alarmed to see that the reported coolant temperature rose rapidly after start-up from cold to read 118 degrees C.
Further investigation led to the discovery of the CHT sensor, which would sense a much higher temperature than the usual ECT arrangement because of its position, fitted in the centre of the cylinder head between spark plugs 2 & 3.
Is the reported temperature typical or should we see a temperature adjusted to reflect the normal range of coolant temperature?
The ECU alledgedly switches the temperature gauge to read either cold, normal or overheating. In this case it never reads above normal.
I,m sure it will have a normal ECT but also a CHT. The purpose of the CHT is if the car is run with-out coolant or low coolant.
If you remove the CHT no water will come out as it actually measure the head temp. and not the coolant.
If there is no coolant in the system the ECT will not read the temp. correctly as it will be sitting in an air pocket. ECT should be on the end of the engine above the G/box. Kev.
I don't think that there is a conventional coolant temp sensor Kev, that reports that actual coolant temp. Autodata wiring diags & component locations doesn't show one anyway & I don't recall seeing one either.
My understanding is that the cylinder head temp sensor is just a different take on a method of reporting engine temperature.
The sensor is a "fit once" component, meaning it should not be refitted, even if it is still serviceable. The brass tip deforms upon installation & mates up with the aluminium perfectly, for correct heat conductivity. If you attempt to refit one, then there is no guarantee that the seating will be correct & the sensor may misreport.
Regarding the point....
"sensing a much higher temperature than the usual ECT arrangement because of its position, fitted in the centre of the cylinder head between spark plugs 2 & 3."
This was raised on UKAT before & there was some interesting discussion on the subject. I can't find the link for some reason.
Ultimately though Steve, the general, overall (mean average if you like) temperature of the cylinder head, should remain within conventional limits I think, so long as there is coolant present. There maybe local hot spots in certain parts of the head, but where there is coolant, the maximum temperature should remain close to 100 - 120 degrees centigrade.
The cylinder head temp sensor comes into its own though, Once coolant is lost, as it will still report accurately, where as the standard temp sensor can run into trouble if it is not immersed in coolant.
You may be correct, but i seem to remember the 02 focus i was using a couple of years ago had both, most likely me just getting old!!!.
Ford use the CHT as a fail safe, if it see,s overheat it will put the guage into the red and cut the engine to two cylinder,s and will even stop the engine completely.
A chap came to me about a year back asking me to fit a water pump on a 02 focus as the temp gauge was all over the place. The head sensor well was full of water and the gauge was going in to the red. Mil on and the car would sometimes stop completely.
Code refeered specifically to cylinder head temp sensor and this was the only reference to engine temp in data.
Rover k series is a good example of not displaying correct temperature as I've seen many over heat or boil up with the gauge sitting in the normal range.
The cht sensor does work well from my experience as we had a ford connect in which cut out after its hose burst. Let it cool down and it was running again.
I reckon they should bring back low oil pressure cut out switches as well but that's another area.
I remembered Elekie's post from years ago but was not aware that some Zetecs, like this one, do not have a separate ECT sensor until I hunted for one in vain...
Serial data shows engine coolant temp. in degrees C and CHT sensor voltage.
I was just concerned that the lean-running condition we were seeing on this engine could be due to too high an engine temperature being seen by the ECU.
The main cause of its lean condition was the common breather valve failure.
on October 27, 2012, 8:16 pm, in reply to "