Yes I do understand that they allow internal gasses to expand and contract with temperature change.
I still can’t see the logic in what your saying is the best route “leave drain hole open, and fit breather”. Why? I’m not trying to be funny, I can’t see any logic in the statement. Why drill the plate, and leave the bottom open, to then fit a plug when you “need” to? Why not fit a breather, if it’s not too exposed, and check it weekly?
I want all my breathers to be fitted all the time, if possible, so I don’t have to do anything when it comes to doing any wading. That’s why the fuel tank and FIP will also be getting extended breathers.
Cool, was just checking.
The reason you fit the wading plug to the bottom of the timing chest only when you need to, is that with it fitted oil can come from internally and get into the timing chest and contaminate the timing belt, if you sealed up the the drain hole by fitting the breather there (or left the drain plug in 24/7) then that oil can’t escape.
Breathers are meant to allow for the expansion of air not the movement of oil and the crud that comes off the belt, so if you breather gets oil in it (It will) then it can form an airlock preventing the breather doing its job, and preventing the drain doing its job.
If the breather is blocked then internal gases expanding as the engine gets hot can cause seals to leak, then if you go into water those gases contract again and with no breather this will cause water to be ‘sucked’ into the timing chest due to the pressure differential (and the previously failed seals due to pressure expansion inside due to heat from the engine)
So you fit the breather high up so that nothing but air goes into it and it remains clear and free-flowing (that’s why they are high in the axles and gearboxes). This is so that the air inside the timing chest can freely expand and contract protecting the seals and not allowing stuff to be ‘sucked’ in through the seals if ‘cold shocked’, and the drain hole down low so that oil/crud runs out by gravity through a large hole as needed.
You leave the breather fitted all the time, then just screw in your wading plug in the drain hole as and when needed (deep water etc) and then take it out again after.
You only leave the wading plug in for short periods of time (few days upto a week would probably be okay).
Fit the breather up high, leave the drain hole open and just look at the drain hole weekly - you would soon see if anything was leaking from the inside and coming out the drain hole - my front seal was leaking and it was obvious as the timing chest ‘funnels’ it all downwards.
You ‘could’ fit a drain plug that has an openable valve on the bottom and just remember to open it and empty it weekly so you don’t cause timing belt failure if stuff builds up inside.
Fitting wading plugs is a 15second job!
Also your fuel tank doesn’t need a breather as it has enough volume to absorb pressure changes like that, and it also doesn’t get ‘hot’ like gearboxes and timing chests. The diesel in it keeps it at ambient temperature so you don’t get the same thermal expansion as other sealed parts of the vehicle.
If you do get water in the fuel tank (unlikely) then just crack the drain screw and the water will come out - water is heavier than diesel. Just make sure your tank cap seals properly when you do it up and the fuel tank will be fine. I have had the fuel filler underwater and it did not take water in.
I don’t like going that deep though tbh.