Monitoring c64 Oil Temperature

Nicolas14 · 3 March 2022 12:38

Hello everyone !

I would like to monitor the oil temperature of the Toyota C64 gearbox on my Lotus Exige S2. Are you guys aware of any solutions for this, e.g. is there a way to plug a oil temperature sensor on the gearbox and link it to a gauge in the car ?

Appreciate your thoughts and sharing of experience

Kind Regards,
Nico

Fonzey · 3 March 2022 12:47

Two pretty easy options:

Replace the drain plug with an M18 (if I remember right) bung with a 1/8npt port tapped into it.
As above, but use the secondary fill plug. There are two fill plugs on the box, one intended for use in a 5 speed and the other which we use in the 6speed variant. The 5pseed one sits a little bit below the fill line of the 6speed one, so you can also use that (as JDS recently pointed out to me).

I’ve been measuring mine from the drain plug for the last year or so, but I’m now losing that port as part of oil cooler plumbing, so I’ll relocate to the 5speed fill plug instead.

You can either use an off the shelf oil temp gauge, or in my case it’s logging to my ECU via my ECUMaster digital dash. Most options will involve a 1/8npt sensor.

Good luck

Nicolas14 · 3 March 2022 14:08

Fantastic !

Thank you for this very clear explanation Fonzey.

Did you really feel the need to an oil cooler ? which temperature have you been seeing ?

Nico

Fonzey · 3 March 2022 16:09

On the road the gearbox settles at a pretty consistent 80deg C. It seems to settle here almost regardless of conditions/usage.

On the track, the temperature gradually climbs and it seems like once it gets around 110dec C, the gains start to get steeper and steeper. Typically this coincides with me ending my sessions, but it feels like around 110deg the casing gets pretty much heatsoaked and really starts to struggle to shed any more temp.

Whether 110deg+ is “too hot” or not for the MT90 oil or the C64 gearbox? Honestly no idea.

I’ve got a pretty big investment in gearbox upgrades now, so I’m adding a cooler to protect that investment. My ECUMaster setup will trigger the cooler to activate around 80 degrees so it’ll be effectively thermostatic, and it will use a water heat exchange from the engine coolant circuit which should hopefully take the edge off a bit and allow me to run longer sessions.

Nicolas14 · 5 March 2022 08:29

Very interesting intel and sharing of experience Fonzey. Thanks for this !
Nico

Carey_Ritchey · 1 January 2025 22:12

All the factory Lotus racecar variants if the Exige included an oil to air cooler for the C64 as well.

andybond · 1 January 2025 22:42

Do you have any details of this ?

IanG · 3 April 2025 06:55

C60-64 Transmission oil cooling

Attached is diagram of transmission oil viscosities at temps - with yellow viscosity cut- off line. Shows your MT90 is ok at 100c.

Have seen Redline that had experienced 150c in a S2 Exige race car and transmission was damaged, probably from thermal expansion of the case and the oil oozed out looking like pink custard - So if you are racing or tracking hard, you will need a transmission cooler.

Attach pic of Lotus Exige offering in about 2010, using a Laminova. Not likely to be available now.

But attach pics of 2 aftermarket kits that are available. Jubu (Austria) and JSR using Laminova. The JSR kit has had good reports. The Laminova w/o is best approach as not much air movement in engine bay.