Gearbox oil temps

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Gearbox oil temps

Postby Aidan » 19 Apr 2018, 07:26

A customer asked me if it was worth fitting one of these
https://www.boxeer.com/collections/parts/products/magnetic-plug-temp-sensor-vanagon-vw-audi-porsche

My take is it might not be that easy to do on a syncro because of the bashplate and on wbx and other engines the exhaust proximity and that it would only be really useful if data logged

Anyone fancy building an ardrino or similar data logger to take oil temps, engine revs and speed data and log it ?

which is what the car builders do during development and testing to determine oil fill volumes and fitness for purpose and life expectancy etc..

Anyway something to talk about......
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Re: Gearbox oil temps

Postby silverbullet » 19 Apr 2018, 10:36

What is a "normal" set of temperature values for an 094 transaxle?
Without baseline data it would be meaningless and just another thing to worry over.
I would reckon that local temps within the transaxle can fluctuate a lot under load, but you'd need thermocouple probes in the casing going right in to the relevant areas, the diff pinion bearing being the obvious one.
But what would it actually tell you?
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Re: Gearbox oil temps

Postby 937carrera » 19 Apr 2018, 11:19

I tend to agree. Why is there a concern over gearbox oil temperatures, is there a history of problems ?

One car which I know has a gearbox oil cooler is the 944 Turbo in the 250hp version- the normally aspirated cars don't have one. I know the T25 Syncro is heavier, so more vwork to do, but unless there is a significantly more powerful engine fitted I struggle to see how so much energy will be transmitted through the gearbox to generate the sort of heat to be worried about. :?:

Wouldn't the formula look something like this ? Energy in = energy out + internal friction losses + radiated heat

My rule of thumb is that transmission losses, including CV' wheel bearings etc is around 15% of flywheel power
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Re: Gearbox oil temps

Postby itchyfeet » 19 Apr 2018, 11:47

There is a post on the FB Group vw t3 vanagon gearbox (getriebe / transmission) & viscous coupling

One reply was ...

I mounted a temperatur sensor in the middle hole like in the pictures from Michael and a temperatur switch at the place shown from Julian, nearer the differential. The switch activates an oil pump for the gear box cooler. Activating temperatur is 70°C. The sensor in the middle shows a little more than 60°C when the switch begins to switch. So, I think, the area near the differential is warmer than a little more away. Driving more than about 115km/h in the dry summer about 70°C were reached (heavy syncro camper with 15 inch wheels, about 4000 rpm). Diving about 130km/h gear box temperatur rises up to about 80°C without cooler ... on a warm dry summer day ... may be more when you drive longer with this speed or more, I don't do that without cooler.
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Re: Gearbox oil temps

Postby silverbullet » 19 Apr 2018, 16:28

That'll be a group that I cannot (and no longer wish to) join :D

Again, what do observed temperatures tell you? VW would have done all this work in the early 1970's and they wont be telling anyone what they know.

Without baseline data from many (zero/20k/40k/60k/80k/100k mile) transmissions tested in all conditions under all loads and duty cycles, its just meaningless numbers.

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Re: Gearbox oil temps

Postby footstuck » 23 Apr 2018, 07:51

A good flow of cool oil directed at the pinion gear has to be the way ahead, and an advantage under all circumstances, and even more so when pulling heavily load van up a long drag.
I think mauling due to high pressure loading and reduced film thickness, is what caused the C&P to fail in my box last time around.
I have a brass headed oil transfer pump set aside for when Aiden fits me a longer C&P set, and I intend to pipe up a cooler circuit to run continually with the aim of permanently reducing C&P temperatures.
This will increasing the oil capacity into the bargain, and I will include a small draw through filter to protect the cleanliness of oil being delivered.
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Re: Gearbox oil temps

Postby 937carrera » 23 Apr 2018, 08:37

One of the comments I picked up when looking at EP performance specs were repeated claims that synthetic oils ran 10 degrees cooler than mineral oils.

Has anyone got experience of this ?

(apologies if this is a light the blue touchpaper question)
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Re: Gearbox oil temps

Postby silverbullet » 23 Apr 2018, 10:38

Oil choice is somewhat dictated by whether the synchronization cones can wipe the oil away and actually "bite" to allow a crunch-free gearchange.
I have been told that the 75W140 work really well in this regard, but have no direct experience.
I do know that a poor choice of oil will definitely have an adverse affect on the quality of the cold shift!

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Re: Gearbox oil temps

Postby jebiga41 » 24 Apr 2018, 10:27

Yep recently saw this, some guys on the continent and states seem to be installing both them and oil temp senders in the boxes but as Ian says unless you have baseline data to compare it too its pointless and just another worry clock plus temp will vary on a number of factors such as on distance travelled, what gear your in , engine choice, ambient air temperature and how well your box can cool itself ( whether its covered in mud or not) etc etc probably better to use the money for an additional oil change????
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Re: Gearbox oil temps

Postby Aidan » 24 Apr 2018, 20:32

footstuck wrote:A good flow of cool oil directed at the pinion gear has to be the way ahead, and an advantage under all circumstances, and even more so when pulling heavily load van up a long drag.
I think mauling due to high pressure loading and reduced film thickness, is what caused the C&P to fail in my box last time around.
I have a brass headed oil transfer pump set aside for when Aiden fits me a longer C&P set, and I intend to pipe up a cooler circuit to run continually with the aim of permanently reducing C&P temperatures.
This will increasing the oil capacity into the bargain, and I will include a small draw through filter to protect the cleanliness of oil being delivered.



AIDAN ffs

so when will you destroy the existing transmission then Nick ?
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Re: Gearbox oil temps

Postby toomanytoys » 24 Apr 2018, 20:36

I have a 6 channel data logger. Maybe now the current project is finished, I can fit His and get some numbers.
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Re: Gearbox oil temps

Postby footstuck » 01 May 2018, 22:29

The current trans will be getting a sustained stress testing next Thursday
I will be towing a loaded car transporter, unless there is a good samaritan who wants to bring my sons accident damaged car back from Bristol to Folkestone.
Any willing volunteer will be saving Aidan a job and another transmission from severe pain, and maybe Death.
And not least. . .my children from going without food for a month or three
Sadly the transmissions are sensitive little things.




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Re: Gearbox oil temps

Postby footstuck » 04 May 2018, 21:18

Might give this a try (depending on feed back), but the last fully synthetic I tried was too slippery for the baulk rings and led to gear crunch. Maybe this is good??
Has anyone tried this oil?
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