oil level sensor for 4HP20 ?

[dieselnutjob]

One thing that's a pain with the later 4HP20 transmission is the lack of a dipstick.
I am wondering if I could replace the level plug with an optical level sensor such as one of these.
http://www.gemssensors.com/content.aspx?id=282

Do you think it could work?
I am thinking then that an LED on the dash that comes on if the oil level drops below the sensor. It would also make it a bit easier to swap the oil in these transmissions as you would would drain, add 4 litres, start engine and then keep adding until the light goes out.

The only problem I can see maybe the oil level would be slightly higher than it should be because normally oil will run out of the bottom of the oil level plug but I'm assuming that the sensor won't flip state until oil is half way up which will be maybe 5mm higher.

And I have to find a sensor that is either the same thread as the level plug, or small enough that I can drill / tap a hole in a spare level plug.

[CitroJim]

A lovely thought but tricky in practice...

Physically, the dipstick hole in the later '20 is a blind hole. It would need drilling out and that's a full strip job. There is a level plug in the diff but the major problem is that oil level varies with the temperature and the levels are vastly different between running and stopped due to the rather quaint overhead sump in the gearbox.

All this makes having an electronic sensor rather impractical really.

Fact is that as long as the right refill procedure is followed to obtain the correct level in the first place and there are no leaks, the gearbox will not use any oil.

In regard to the latter, I squint under the car once a week and one of my checks is to ensure the gearbox, driveshaft seals and half-moon plate on the bellhousing are all bone-dry.

The couple of times I've found damp in the vicinity it has always turned out to be LHM The '20 is a pretty oil-tight 'box generally although driveshaft seals do occasionally fail.

[dieselnutjob]

A lovely thought but tricky in practice...

There is a level plug in the diff but the major problem is that oil level varies with the temperature and the levels are vastly different between running and stopped due to the rather quaint overhead sump in the gearbox.

The oil level is higher when the engine isn't running.
So. If the oil is at sensor height with the engine running then it will be higher when the engine is stopped, and so the warning will be off.
If the oil level varies that much then it does kind of indicate that the exact level isn't that critical provided there is enough in there.

I am kind of thinking that provided that the sensor can see oil at a warm ,level, tickover, then the rest of the time I can ignore it.

Maybe it would be best with a push button so that the old level could be checked periodically when the car is level, warm and running.

[CitroJim]

Maybe it would be best with a push button so that the old level could be checked periodically when the car is level, warm and running.

That would work a treat

The level plug on the diff is reasonably accessible so the scheme should work well...

Not sure of the thread size but it's not all that big. M6 I think...

[dieselnutjob]

I bought a spare plug, but left it on my desk at work. M10 I would say. Can tell you for sure after Easter.

[dieselnutjob]

appears to be M12x1.5

Jim, can you tell me if there is anything that would hit a sensor if it pokes into the case further than a drain plug?