Best place to fit an engine coolant temperature sensor

[Toilet Duck]

Afternoon all,

I want to fit a decent water temp guage to my car rather than relying on the wildly fluctuating existing digital readout on the dash.

Where is the "best" place in the coolant circuit to fit the sensor? I assume you want to monitor the water at the hottest place, so could I connect into the hose where the water leaves the engine on it's way to the radiator (I'm guessing it would be hottest at this point prior to getting cooled when it reaches the radiator?)?

Cheers for any help

[cuprabob]

Before the thermostat, so you can detect if it doesn't open.

[Toilet Duck]

cuprabob said:

Before the thermostat, so you can detect if it doesn't open.

Ah...... didn't think of that! I'm guessing that will mean having to machine a "hole" for the sensor then as I assume that will be on the block somewhere and I doubt there will be a hose at that point to splice and put a T-piece type connector in. It's a Honda K20 engine.

Thanks very much!

[Penelope Stopit]

Visit here, you might find it does the job https://www.ebay.com/p/Black-32mm-Water-Temperatur...

[99hjhm]

You want to measure the coolant temperature as it exits the engine imo, thermostat housing is ideal, but many OEM’s use rear of cylinder head too.

[stevieturbo]

Toilet Duck said:

Afternoon all,

I want to fit a decent water temp guage to my car rather than relying on the wildly fluctuating existing digital readout on the dash.

Where is the "best" place in the coolant circuit to fit the sensor? I assume you want to monitor the water at the hottest place, so could I connect into the hose where the water leaves the engine on it's way to the radiator (I'm guessing it would be hottest at this point prior to getting cooled when it reaches the radiator?)?

Cheers for any help

What is your definition of a decent water temp gauge ? And exactly what car..and in what respect is it wildly fluctuating ?

[Toilet Duck]

stevieturbo said:

What is your definition of a decent water temp gauge ? And exactly what car..and in what respect is it wildly fluctuating ?

Hello Steve

Car is an Ariel Atom with supercharged Honda K20 engine. Water temp is currently displayed digitally on the OE instrument cluster. The issue I have on track is the temperature can shift in circa 6 degree increments when I've been out on track a while and the car is "hot". For example, the water temp may show 98 deg C then when it updates (which it seems to be roughly every 1 second) jump to 104 deg C, and then back to something else. I'm not sure if the readings are accurate or if it's a "smoothing" issue with how the actual temperature readings are updated/displayed etc. The Atom isn't know for "accuracy" with some of the readouts, especially the fuel guage. From what I understand of the K20 engine, there appears to be two temperature sensors. One feeds the ECU and one triggers the radiator fan. I'm not sure what one feeds the Atom instrument cluster. It could be that the ECU temp feed is a lot more "accurate" and that there isn't anything to be concerned with in terms of coolant temp.However I'd rather be able to monitor myself!

I was looking to complement the OE temp readout with something like this:



I would hope that this guage would be classed as "decent" but welcome any opinions/other suggestions?

I also want to monitor oil temps (something not displayed on the OE set up) as per my other thread about oil coolers etc

Many thanks!

[GreenV8S]

Should be easy enough to find which sensor the dash uses by seeing the initial (cold) value with ignition on/engine stopped, then connecting a known resistance in place of the sensor and seeing whether the reading changes (still ignition on/engine stopped).

The sensor will most likely be a thermistor with a resistance of a few kOhms at room temperature which drops as the temperature rises, but it will be easy enough for you to confirm that - you will need to know the working resistance range to pick a suitable resistance value for substitution.

Assuming the dash has its own temp sender as you seem to be implying, you might consider disconnecting it from the dash and connecting it to your aftermarket gauge instead - the OEM sensor will be in the ideal position for what you want.

Are you able to see what the ECU thinks the coolant temp is, for example via OBD2? It is IMO more important for that to be right than for the gauge to be accurate.

Are your fans controlled electronically, or via an otter switch?

[stevieturbo]

Are you implying it jumps at 1s intervals from 98 to 104 and back to 98 again ?

Exactly what are they using for a dash ?

Coolant temperature sensors by nature tend to have very slow response times anyway...so rapid changes would be more indicative of a fault, wiring or otherwise.

As a "new" vehicle...presumably it is fully OBD compliant ? If so, just get a cheap OBD reader and view the live data for coolant temp there.

[Toilet Duck]

stevieturbo said:

Are you implying it jumps at 1s intervals from 98 to 104 and back to 98 again ?

Yeah, exactly that. It jumps all over the place when it gets hot on track at something in the region of 1s intervals. Even on a cool down lap it jumps around, its as if when it goes past a certain temp it starts varying wildly. Ive seen it hit 110 deg C+ before but because it jumps so quickly I dont know how accurate it really is (I obviously lay off the loud pedal when it starts going high like that and let it cool down/stabilise). During road use it doesn't fluctuate wildly at all.

stevieturbo said:

Exactly what are they using for a dash ?

one of these

I will give he cheap OBD reader a go as also suggested by GreenV8S and see what info (if any) that gives. The trouble is its a bastardised Honda ECU with Hondata flash as used by the factory, I have a vague recollection of trying an OBD reader on this a few years ago and seem to recall it not giving out any/much info. The other thing is as this issue only applies when driving hard on track, it may be tricky to do a comparison of the OE temp readout and an OBD reader connected to a tablet/mobile phone during a track day

I definitely want to fit an oil temp guage so thought this would be a good opportunity to also get an "external" water temp reading as well that circumvents the current OE unreliable set up.

Cheers for your help :-)

[GreenV8S]

Toilet Duck said:

one of these

That page suggests that the dashboard is directly connected to the temp senders and shows what look like a couple of generic two-pin thermisters.

With relatively little work you should be able to work out which physical sensor is driving the dash temp readout and work out the resistance/temperature characteristics of the sensor. I assume the dash is measuring the resistance using an A2D conversion and you should be able to find the resolution of that conversion by putting a potentiometer in place of the sensor and slowly adjusting it through the 'hot' resistance range. It shouldn't be hard to work out whether the behaviour you're seeing is a limitation of the dash/sensor design or some problem that you could address e.g. by better voltage regulation or fixing a poor connection.