Wiring an oil temperature gauge

[griffchris]

Hi, I know this is a subject that has been at least partially covered in a number of previous threads but I'm after a bit of clarification before i embark on it.  I plan to wire into the existing water temp gauge and use an indicator or main/dip beam switch:

I have a 2015 420R self build with dry sump.  The threaded oil temperature sensor is already fitted to the dry sump tower.  I've heard mention that the wiring for the oil temp sensor should already be in place (and the R400 wiring diagram in the manual displays it, though I'm not really sure how to interpret the diagram!) - any idea where this wiring is and what it looks like?  I've found a Black/green pair which I must have tie wrapped out of the way on the left side of the engine bay, as per photo, is this the right one - I don't think this which reach to the sensor on the dry sump tower as is anyway so would need extending?

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Assuming I can find the correct wiring in the engine bay, be it the above or something else, will the other end of the wiring be conveniently tied off somewhere under the dash, ready to attach to the switch/gauge?

Apologies if I've got this completely wrong.  Alternatively, if I need to run new wiring the whole way, what wiring and teminals would I need?

Thanks for any help.

Chris

[ScottR400D]

I did this to my 2015 R400D. 3 pole switch on dash under water temp gauge. Wire from oil tank sensor to one side of switch. Wire from water temp sensor to other side of switch. Wire from central pole of switch back to loom where water temp sensor originally connected.

I replaced both sensors with similar ones that have same rating but M4(?) thread connectors so that wires can be connected with a crimped on ring connector and nut rather than spades; the switch has standard spade connectors.  

Switch one way gives water temp, in middle nothing, other way reads oil.

Very easy to fit and works fine. Only questions are whether low down the oil tank is best place for sensor and what temperature range should be there. No way of knowing what it is pre being cooled.

On the road mine runs at 60/70c and 80c or so on a track day. I guess that's OK as it runs well, isn't otherwise modified and measuring there just sets a standard to use as a reference so I know when the oil has warmed up.

I'll try to get images and switch details for you later if you're interested?

 

[griffchris]

Thanks Scott, any images and further details you can provide would be great!  So, did you run your own wire from the oil temp sensor through the tunnel to the under-dash area, or did you make use of an existing (redundant?) connection for (part of) the way?

[Jonathan Kay]

I wouldn't start this without the wiring diagram, table of standard colours (which might not match yours) and a multimeter.

I'm not really sure how to interpret the diagram!

Where have you got stuck? Is it with the colours, the numbered ways in a schematic or something else?

Switch one way gives water temp, in middle nothing, other way reads oil.

is that better than a two position switch? Wasn't there a discussion about whether to use one that sits in either position or one that is sprung to water but can be manually held over for oil?

...

Black/ Green is conventionally "Relay to radiator fan motor" but again might not be in your car. I'd test that directly.

Jonathan

[SM25T]

If in doubt ... Just run a single core from oil temperature sender to the new switch. Indicator switch is useful as it gives a complete break between each incoming signal ... And doubles up as a spare indicator switch in case of breakage. Run the wire around the chassis tubes and through the big grommet in the tunnel top forward of the gearstick.

[ScottR400D]

Hi Jonathan. 

I did it the way I did because it's very simple and easily reversible. (Other than the hole for the switch!) 

Yes, a switch without the central 'off' position might have been better but I couldn't find a good one and I do t find it an issue. The one I got is good quality and waterproof, for what that's worth!

I don't think a sprung one would be good because the sensors and/or gauge are heavily damped; it takes several seconds to adjust, especially if the oil is warming up and there's a significant, say 30 degree difference between water and oil. I wouldn't want my hand off the wheel for that long. Also there are times when I want to monitor the oil, e.g. cooling down on track. 

I'm sue there are many options but this works for me. Simple, effective and reliable without interfering with the loom. 

I'll get some pics and post them later.

Peter Scott

 

 

[ScottR400D]

Chris, I used completely new wires. A SM25T hints, it avoids any doubt and is very straightforward. I couldn't get it through the big grommet, that's pretty much chock full. I drilled a 6mm hole next to the heater, put a grommet in it and fed the wires through there then directly to the switch. 

Peter. 

 

[griffchris]

Thanks all, very useful - I'll run a new wire then, sounds like the safest solution - errrr very basic but what gauge wire should one use?!!!

Chris

P.S. Sorry Peter, I had assumed your name was Scott!!

[ScottR400D]

No problem! My own fault for using the silly username, you're not the first! Will take pics soon and check wire size. 

[Jonathan Kay]

I'll run a new wire then, sounds like the safest solution

I'd try and fine that existing one if you think it exists. Found any other candidates?

what gauge wire should one use?

Anything at least as big as the current one for the water temperature. Conventional colour would be White/Brown.

Jonathan

[Jonathan Kay]

And doubles up as a spare indicator switch in case of breakage.

I don't think a sprung one would be good because the sensors and/or gauge are heavily damped; it takes several seconds to adjust,

Good points. And always nice to have options.

Jonathan

[ScottR400D]

 

This image shows the connection to the water sensor. The green wire is the original and now runs as the black one to the centre switch.  The blue goes from the sensor to the switch (I take JK's point about colouring and I may redo mine next year but for now its a very simple stand alone bit of wiring). I used 8A cable but 5A would have been more than enough. I felt that the connectors fitted better to the slightly thicker cable.

This one shows where all three wires (red from the oil sensor, blue from the water sensor and black for the gauge wire) come together and run through the bulkhead to the switch.

This one show the switch with its waterproof cover.

[ScottR400D]

By the way JK, if you remember the thread about engine earthing points, you can see in the second image where my engine is earthed to.

It is an M8 steel threaded insert and shows good continuity so far, after 18 months or so, but I'll be keeping an eye on it. As all three elements, the bolt, insert and cable end are zinc plated and its in a quite dry area, hopefully dissimilar metal corrosion wont be an issue.

[Jonathan Kay]

3 pictures ≈ 3k words.

:-)

Jonathan

[SM25T]

Big grommet is very stretchy. You can fit loads more through it. Shove a bit of dowel through from above and tape new wire to it ... then pull it back.