Here's my story. Got myself a C-Max 2017 at an auction. Turned out the engine had extensive internal damage, so I replaced it with a new unit from Pumaspeed, along with new injectors, brakes, clutch, etc. I took my time to replace everything I thought needed replacing for peace of mind. I was ready to start the new engine for the first time yesterday but as soon as I turned the ignition on (key is a proximity one), a message popped up suggesting 'engine temp was too high' with the needle jumping to max, as shown in image below.

Your help will be greatly appreciated. I should add that I got a new (genuine Ford) coolant temp sensor this morning but there has been no change. Could the message be from the last time the engine broke?

Hi,

This is usually just caused by low battery.

Have you replaced or at least charged the battery while it's been off the road?

First it is important to know which temperature sensor is registering the overheating.

Unlike the earlier 1.0 EcoBoost engines the later 1.0 EcoBoost engines (including 2017) have 2 different temperature sensors. The standard coolant temperature sensor and the additional cylinder head temperature sensor. Both can register overheating.

Also check whether the wiring harness is connected correctly. Some of the sensors have the exact same connector. After an engine replacement it is not uncommon to have connectors mixed up.

1 hour ago, TomsFocus said:

Hi,

This is usually just caused by low battery.

Have you replaced or at least charged the battery while it's been off the road?

Thank you so much. I have put the battery on charge and will check once it's fully charged.

My apologies, the picture didn't show first time I opened the thread.  I misread it as all needles going to max. 

I agree with Wilco that this is likely to be related to a temp sensor. 

1 hour ago, JW1982 said:

First it is important to know which temperature sensor is registering the overheating.

Unlike the earlier 1.0 EcoBoost engines the later 1.0 EcoBoost engines (including 2017) have 2 different temperature sensors. The standard coolant temperature sensor and the additional cylinder head temperature sensor. Both can register overheating.

Also check whether the wiring harness is connected correctly. Some of the sensors have the exact same connector. After an engine replacement it is not uncommon to have connectors mixed up.

Thank you so much. I did notice the other sensor on the head. I shall check everything again. Is there a way to determine which of the two could be faulty. I am thinking it might be the one on the head as I have a brand new OEM one on the thermo housing.

2 minutes ago, TomsFocus said:

My apologies, the picture didn't show first time I opened the thread.  I misread it as all needles going to max. 

I agree with Wilco that this is likely to be related to a temp sensor. 

Thanks again Tom. That really helps narrow the problem down. I shall check the wiring very carefully in daylight tomorrow and also order the other sensor. Would there be any change I should see (expect) if I disconnected the 'defective' sensor. I am thinking maybe disconnecting them one at a time might point to the faulty one.

FORScan should be able to give tell the individual temperatures that both Sensors are registering .

I suspect that one of the temperature sensors has the wrong wire plunged in. As Wilco has already said some parts use the same plugs and it's easy to get them mixed up.

As a quick check unplug both sensors and see if the gauge drops.

1 hour ago, unofix said:

I suspect that one of the temperature sensors has the wrong wire plunged in. As Wilco has already said some parts use the same plugs and it's easy to get them mixed up.

As a quick check unplug both sensors and see if the gauge drops.

The gauge dropped when I unplugged the new sensor (installed today)on the thermo housing (connector is grey).

Just now, Kilimanjaro said:

The gauge dropped when I unplugged the new sensor (installed today)on the thermo housing (connector is grey).

Should have added that there was no change when I unplugged the sensor on the cyl head.

5 minutes ago, Kilimanjaro said:

The gauge dropped when I unplugged the new sensor (installed today)on the thermo housing (connector is grey).

That would say that to me that there is a problem with that sensor., either the new sensor is the wrong type or it is faulty.

Do you have a multimeter ? If so check the resistance of the new sensor.

1 hour ago, unofix said:

That would say that to me that there is a problem with that sensor., either the new sensor is the wrong type or it is faulty.

Do you have a multimeter ? If so check the resistance of the new sensor.

Thanks. I do have a multimeter. What should the resistance be? I did notice the connector looked damp/oily but thought nothing of it. Could that maybe be bridging the pins.

8 minutes ago, Kilimanjaro said:

Could that maybe be bridging the pins.

That sounds very possible.

give it a good clean, and spray with electrical contact cleaner, or WD40.

On 12/6/2021 at 10:17 PM, unofix said:

Below is a table of sensor resistance / voltages which might help. The values should be +or- 5%

 

 

9 minutes ago, unofix said:

That sounds very possible.

give it a good clean, and spray with electrical contact cleaner, or WD40.

 

Thanks again. I shall update tomorrow after I try everything you have suggested. Good night.

20 hours ago, Kilimanjaro said:

Thanks again. I shall update tomorrow after I try everything you have suggested. Good night.

 

20 hours ago, unofix said:

That sounds very possible.

give it a good clean, and spray with electrical contact cleaner, or WD40.

 

Update. I did everything we discussed yesterday but there was no change. I also went ahead and started the engine which ran very smoothly but I could hear a fan running though I had turned the AC off. Engine temperature warning continued to be displayed along with the orange check engine symbol. i have asked a friend with scanning software to run a scan for me tomorrow.

Have you compared the resistance of the new sensor against the old sensor ?

What resistance value are you getting ?

22 minutes ago, unofix said:

Have you compared the resistance of the new sensor against the old sensor ?

What resistance value are you getting ?

I replaced the 'new' sensor with another new genuine Ford one (1702985) but did not get round to testing resistance. I will have more time tomorrow and will do the tests. I wonder if it could be 'memory' that needs clearing.

1 hour ago, Kilimanjaro said:

I wonder if it could be 'memory' that needs clearing.

No.

Doubtful. Temperature is a real time measurement. If the car senses a high temperature it will run the fan. Disconnecting the new sensor should stop it. As the gauge falls on disconnection, the sensor wiring is not shorted to ground so try swapping in the old sensor if you still have it.

1 hour ago, anon said:

Disconnecting the new sensor should stop it

Not the case on Ford's. Disconnecting the temperature sensor will make the radiator fan run continuously, it is designed as a fail safe system.

3 hours ago, anon said:

Doubtful. Temperature is a real time measurement. If the car senses a high temperature it will run the fan. Disconnecting the new sensor should stop it. As the gauge falls on disconnection, the sensor wiring is not shorted to ground so try swapping in the old sensor if you still have it.

Thanks. But this is happening on a non-running stone-cold engine. Message pops up as soon as ignition is turned to on...with the fan kicking in as soon as the engine is started. I now have two new genuine sensors for the thermo housing. I am thinking that I should maybe try a new sensor for the head. I shall test the both sensors for resistance as Tom suggested and post the values here.

Update. My friend ran a scan using FORSCAN and several codes popped up. We cleared all the DTCs that came up and everything returned to normal. Engine temperature message and check engine light did not show up again in the thirty minutes I kept the engine running. Temperature gauge looks normal too and the fan stopped continuous running. Car has no MOT so I could not drive it far...but all good for now. Thank you all.

UPDATE: Car now has MOT and I have done about 500 miles. No issues have arisen. I now want to change the alternator pulley. Would you guys know what tools I need, thanks.

There are specific tool sets for alternator pulleys.  Generally one long Torx bit and one socket with a hole in to counter hold the nut.  You might find it cheaper to have this job done at a local garage than buying the tools for just one use.