"Best" location for engine coolant temperature sensor

[Toilet Duck]

Afternoon all,

I want to fit another temperature sensor to my AA3 to feed an auxiliary water/oil temp gauge that I've recently fitted:



I'm struggling to find anywhere to position the temperature sensor for the water (I've taken care of the oil temp sensor). Ideally I wanted to position it in the head where the water temps will be highest, but I'm struggling to find anywhere where I can tap into?

Worst case, and this is far from ideal, I could tee into one of the main water pipes going to/from the radiator. This isn't ideal as I won't get a temp reading during initial warm up until the thermostat opens. However, I can't currently run my engine up to check which is the "hot" side as I've drained the coolant. Does anyone know the direction of coolant from the engine i.e. does it leave the head down the main flexi water hose down to the electric water pump and off to the front radiator, or does it exit the engine from the hose coming off the thermostat housing and then off to the front radiator? Normally the engine coolant "escapes" at the thermostat and off to the radiator once its opened after the temps rise enough. However, googling has suggested that on the K20 the water may flow from the radiator and back into the engine at the thermostat location, which is not "normal".

Easy way to check which is the hot side is to start engine from cold and wait until the thermostat opens - the flow towards the radiator will heat up noticeably quicker than the return back to the engine from the radiator, you can easily feel this with your hand. However, I can't do this as I've already drained the coolant!

Any help appreciated!

[HenryJS]

Left hand Pipe underneath is

Engine => Rad

[smokin]

(Hope this is applicable to AA3 as well as AA2)

In terms of coolant flow, from what I can tell:

• It exits the block via the outlet assembly (9). The long fat flexi pipe with the in-line fan switch connects this assembly to the rad input. The medium sized pipe (13) connects to the thermostat bypass. The smaller hose goes to the throttle body

• The rad output goes to the electric water pump input

• The water pump output goes to the thermostat large input

• Thermostat output connects by return pipe (15) to block via joiner (12)

So pipes 15 and 13 are always on

Some options off-the-top:

• There's a coolant drain plug on the block that you could hijack (27) it's M14 so may need adapting or

• Tap into the bypass (13/15) maybe at joint (12) or

• You could swap out the sender for the dash that sits on top of the outlet assembly (9) if you don't intend looking at the dash temp display or

• You could swap out the two-wire ECT sensor (19) for a three-wire (which has two thermistors inside) but you'd need to find one that satisfies both the ECU and your external display

[Toilet Duck]

Thank you both

smokin, I hope you are going to hang around despite having your atom up for sale, you really are an oracle when it comes to atom technical stuff. Lost count of the number of times you've helped me out

cheers

[smokin]

Always happy to help. I'll try to pop in now and then

[smokin]

Did you find a solution TD?

[Toilet Duck]

Did you find a solution TD?

Yes! Im going to put the sensor on pipe no. 15 in the diagram you posted above. I've got a local fabricator making me up a short section of 20mm pipe with a threaded boss welded on to accept my sensor. Will post up a pic once I collect and fit it.

Cheers

[smokin]

Sounds like it should be an elegant solution and won't interfere with anything else

[Toilet Duck]

Couple of pics as promised:

[smokin]

Looks good