Engine Coolant Sensor not receiving water

[LondonTown32]

Hi Guys,

I really need some help and wondered if anyone can shed some light on a bizarre problem I've occurred with my ford focus mark 1? I'll try and keep it short and simple so as to avoid confusing you! Basically, I initially had a problem with one of my engine core plugs, it had eroded and had developed a hole which caused my engine to overheat due to loss of water. From what I've read it seems that engine core plug erosion problems are very common on the ford focus's. Anyhow, my mechanic replaced the core plugs last week, also a new coolant sensor and spark plugs etc. Car was fine for around a day or so and then whilst driving my engine overheat warning light came on, I pulled over and first thing I did was check my water levels in case of a leaky core plug again. Water levels were fine and engine was not overheating, just seems that the car thinks it was. So, I was able to see my mechanic today, we suspected that the sensor may be faulty as there were no obvious signs that the engine was actually overheating. He checked the thermostat temp and engine temp with a special infrared gun and all readings came back normal. Thermostat was definitely opening and water was cooling the engine as normal. He also ran a diagnostics check and everything came back normal, yet the car is still going into overheat mode: Fan comes on and engine overheat lights - but the engine is defo not overheating, car just thinks it is! We eventually found the problem, but it is very bizarre and strange. Basically, he removed the engine temp sensor and discovered that sensor was not sitting in water, which means if it is not getting the water then it cannot read the correct engine temp and hence why my car keeps going in to overheat mode. When my mechanic removed the old sensor last week, the water spouted up as soon as he removed it, so we know there was def water getting to it last week. It appears the problem has risen since he fitted the new core plugs last week, has anyone else had this problem or would possibly know why the water is not getting to the sensor. My mechanic is very good, I have known him for 8 years and he said he has never seen this before. Tomorrow he is going to try and replace the core plugs again to see if may be he originally pushed them too low or something. Although it seems they are fitted perfectly well. Can anyone shed any light on this issue? I would really apprecate any help on this one, apologies if it has taken ages to read but felt I should give you as much information as possible. Thanks.

[mjt]

I don't know where the sensor is in your engine but the most obvious answer is that there is an airlock at that point because when refilling with coolant not all the air was purged out. Some engines need to be vacuum filled to eliminate air pockets.

[LondonTown32]

Hi, thanks for your reply, he did check this and ruled it out but it's looking like we are running out of options so he will have to double check this again tomorrow. It has to be something!! Thanks again. P.s: The sensor sits inbetween spark plugs 2 and 3 above cylinder head.

[iantt]

so your temp guage was reading high also?

and why did he change coolant sensor?

[LondonTown32]

Because the spark plugs, and sensor areas were all drowned out with water when I had the initial water leak via the core plugs, the sensor sits right next to the core plugs. Hence got damaged by the water as well as the spark plugs. Yes, the temp gauge goes right up to the red but the engine is not overheating. Sensor is giving a false reading as it has no water.

[iantt]

sensor drowned in water shouldnt affect its function when dried out. does the temp gauge go up quickly even with a cold engine? 

when a temp sensor is not surrounded by coolant , normally the oposite effect happens, the temp gauge shows cold/cooler. sensor relys on the coolant to transfer the temp

has your mechanic checked the sensor resistance values at different points in the warming up cycle i.e 2.5 -3.5kohms is 90c 7-8kohms is 60c. 25-28kohms is 30c. etc, also can be done by checking reference voltage/  signal voltages

[LondonTown32]

Hi, no the temp gauge does not go up quickly with a cold engine. It usually happens a little while after driving, sometimes quicker on hotter days. To tell a lie actually, on one of the diagnostic checks on engine temp, the car was telling the computer that the cylinder temp was around 117 C, but it definitely was not that temperaure in reality as like I said previously, we checked the real temp which was coming back normal. The main issue is why no water is getting through to the sensor? Very baffling. Thanks again for your help.

[JW1982]

What type of engine do you have? As far as I remember this is a known problem of the focus MK1 with the 1.4/1.6 engine. The original temperature sensors are no longer available. The new sensors are slightly different from the old sensors and cause problems in some rare cases. If you still have the old sensor you should put it back as this will most likely solve the problem.

If you do not have the old sensor and the problem persists while the engine temperature is fine you either can search for the old original type of sensor (which are very rare) or you have to find a different solution. A known workaround for this problem is installing an additional resistor between the sensor wiring. From what I remember the value of this resistor should be about 330 Ohm. Be aware that this workarround should only be applied if there are absolutely no cooling system problems and the problem is caused for 100% by the new sensor.

[LondonTown32]

Thanks for the advice, could I ask if you know if the CHT sensor is meant to sit in water or does it read the engine temp from the metal? Ford Focus 98-2004 Mk1 model.

[Tdci-Peter]

On 25/07/2016 at 10:02 PM, LondonTown32 said:

Basically, he removed the engine temp sensor and discovered that sensor was not sitting in water, which means if it is not getting the water then it cannot read the correct engine temp and hence why my car keeps going in to overheat mode. When my mechanic removed the old sensor last week, the water spouted up as soon as he removed it,...

...My mechanic is very good, I have known him for 8 years

Has the car been back to the garage yet? Any news?

I would tackle the problem from the other end. If the sensor is intended to run dry, then it will sit inside a small, blind hole in the head, probably with a fairly close fit to the sensor. Perhaps water had got in there from the leak, and that is what "spouted out"

If the sensor is intended to be wet, the hole will go through into the main water jacket. Then the following problem arises:

Part of the cylinder head that used to contain coolant, now appears to be dry. Suggests either air is trapped inside the head, (though surely that would escape once the sensor was removed), or some blockage is preventing water circulation inside the head? If water is not circulating, there will be local overheating. That would need urgent attention.

If blockage in the head can be eliminated, then it would appear the new sensor is either faulty, or the wrong resistance, as Ian & Wilco say.

It should be easy to see from the hole (with sensor removed) which it is. Any help?