delta on reading between IAT and CLT

[Yves]

I'm rewiring my engine and just finished the wiring of my CLT and IAT. I'm using shielded wire this time.

For some reason I seem to be having a delta on the reading between the 2 sensors, which I didn't have before. The CLT reads 46 degrees and the IAT 52. I'm working in a heated garage. Could this have to do with the block not heating up this fast and staying on a low temp or is this something more ?

[nathaninwa]

Are they both the same sensor like a gm unit? One closed for collant and one open for air? In a heated garage I wouldn't be to worried about 4* difference with an open/closed sensor.

[Yves]

I'm going to retry tomorrow when the garage has cooled down.

[lagos]

I normally see a 10F delta between the two sensors on a cold engine as well. They never seem to reach equilibrium, which is odd.

[LAV1000]

First check the calibration tools.
Are they set the same way/value.

If you want to make sure, disconnect and unscrew both sensors and leave them for say 0.5 hour at roomtemp.
Then get a multimeter and measure the resistance (Ohm) should be close.
Those sensors also have tolerances.


When sensor is connected it drawns current.
Each type sensor has a max current, if there is more current the sensor heats up.
On a coolant sensor this has little effect because it has a lot fluid/mass heat sink.
The air sensor not so much, but this evens out whit a running engine/ airflow.

[Yves]

Ok, the check with a stone cold garage didn't give a difference, still 47/50°F.

[LAV1000]

In for an expiriment ?
Get that IAT sensor out.
Put it in open air at same hight as the lowest point of the engine housing.
Leave it there for an hour or so and log again.

[Yves]

In for an expiriment ?
Get that IAT sensor out.
Put it in open air at same hight as the lowest point of the engine housing.
Leave it there for an hour or so and log again.

Too late here now, but will try this tomorrow or so.

Could it be that it's showing different because it's not attached to the engine (ground ? )

My digital infra red thermometer says the block is 8.5°C which is close to the reading I'm getting from the CLT.

[dontz125]

Both sensors should use the same wiring, with the 'sensor' wire on one side and the 'sensor return' on the other. Anything else will result in an offset.

[Yves]

Now you have me wondering. The relay board I'm using has a IAT return and CLT return. So both have their own return(ground) to the board.

[Yves]

Now you have me wondering. The relay board I'm using has a IAT return and CLT return. So both have their own return(ground) to the board.

anyone care to comment on this ?

[Matt Cramer]

Now you have me wondering. The relay board I'm using has a IAT return and CLT return. So both have their own return(ground) to the board.

anyone care to comment on this ?

All returns are sent to a single ground on pin 19 on the relay board.

[Yves]

Now you have me wondering. The relay board I'm using has a IAT return and CLT return. So both have their own return(ground) to the board.

anyone care to comment on this ?

All returns are sent to a single ground on pin 19 on the relay board.

So that can be excluded as the cause.