Ecu water temp only reading 56 degrees

[Discopotatoes]

I'm just finalising my nut and bolt restore, and run the car upto temperature yesterday, the dash gauge was reading 70 which isn't that accurate tbh, the ecu temp read 56 but when I put a thermal laser on it that read 90 degs. If I unplug it, it goes to 110degs on the ecu software which is what I've set it to read if the sensor fails.
I don't think it's sitting in an air pocket as where it is there is plenty of flow. So is there any reason for it to read low like this?

Thanks in advance

[227bhp]

Discopotatoes said:

I'm just finalising my nut and bolt restore, and run the car upto temperature yesterday, the dash gauge was reading 70 which isn't that accurate tbh, the ecu temp read 56 but when I put a thermal laser on it that read 90 degs. If I unplug it, it goes to 110degs on the ecu software which is what I've set it to read if the sensor fails.
I don't think it's sitting in an air pocket as where it is there is plenty of flow. So is there any reason for it to read low like this?

Thanks in advance

It's possibly broken.

I wouldn't place too much accuracy on one of those laser temp reader things, they give different readings dependent on surface texture, colour, reflectivity etc. A traditional thermometer and a bowl of hot water would be far more accurate.

[GreenV8S]

Some engines have multiple sensors - for example my V8S has three for the coolant plus one for fuel. If in doubt, make sure the sensor you're using is the correct one.

These sensors are usually thermistors where the resistance drops as the temperature rises; any extra resistance in the circuit tends to make them read cool. If you haven't already, make sure the contacts are clean.

ECU temp senders in my experience tend to be two wire (power and ground). If yours is a single wire sensor then it would be using the vehicle chassis for ground and any voltage difference between ECU ground and vehicle ground could cause a misreading - this is the sort of thing that could creep in unnoticed while connectors and earthing points were left exposed to corrosion during the rebuild.

[Discopotatoes]

GreenV8S said:

Some engines have multiple sensors - for example my V8S has three for the coolant plus one for fuel. If in doubt, make sure the sensor you're using is the correct one.

These sensors are usually thermistors where the resistance drops as the temperature rises; any extra resistance in the circuit tends to make them read cool. If you haven't already, make sure the contacts are clean.

ECU temp senders in my experience tend to be two wire (power and ground). If yours is a single wire sensor then it would be using the vehicle chassis for ground and any voltage difference between ECU ground and vehicle ground could cause a misreading - this is the sort of thing that could creep in unnoticed while connectors and earthing points were left exposed to corrosion during the rebuild.

Thanks, this is on a Chimaera, I did move the engine ground and upgrade it to 35mm2 from the back of the near side block to the ground point under the dash so maybe that has something to do with it, I'll check the connectors on the sensor for corrosion too

[Krikkit]

Depending on the sensor you might be able to find its nominal resistance at a particular temperature, in which case thermometer + jug of water would be a good test if it's removable.

[GreenV8S]

Discopotatoes said:

Thanks, this is on a Chimaera

Is it using the original 14CUX ECU and corresponding coolant temp sender?

[Discopotatoes]

GreenV8S said:

Discopotatoes said:

Thanks, this is on a Chimaera

Is it using the original 14CUX ECU and corresponding coolant temp sender?

No it's using a DTA p8 pro, it's the standard rover v8 sender and was working fine before the restoration

[Discopotatoes]

Krikkit said:

Depending on the sensor you might be able to find its nominal resistance at a particular temperature, in which case thermometer + jug of water would be a good test if it's removable.

I'll give this a try

[stevieturbo]

You've more or less proven the wiring is intact, as reading changes to default value when unplugged.

So most likely it is a faulty sensor. Try another and see what happens, or stick a variable resistor across the terminals and see if the reading changes as you adjust. Again that will prove the wiring and ecu etc

[Discopotatoes]

stevieturbo said:

You've more or less proven the wiring is intact, as reading changes to default value when unplugged.

So most likely it is a faulty sensor. Try another and see what happens, or stick a variable resistor across the terminals and see if the reading changes as you adjust. Again that will prove the wiring and ecu etc

i already have one ordered so i shall see what happens, thanks

[GreenV8S]

Discopotatoes said:

No it's using a DTA p8 pro, it's the standard rover v8 sender and was working fine before the restoration

In that case the nominal resistance should be approximately 6KOhms at 0C, roughly halving for each 20C above that. These are rough figures for a sanity check - don't use these to calibrate anything.