Mixing oils. How careful should I be?

[Father Ted]

I have a 12v pump bought from Lidl which I use to do my ATF oil once a year (2 litres out, 2 litres fresh in).
I have always been careful not to let the pump or pipes come into contact with any other oil.
I will be doing my bevel gear (transfer box) oil in the next few weeks (or months....) and was thinking of using the same pump.

My thinking is this: the first use will be to remove the old oil, thus purging the pump of the alternative oil type. So, when I turn it around to refill, I won't be pumping a small amount of ATF into the transfer case. And, when I do the ATF in spring, I will purge the gear oil from the pump when I take out the ATF and won't be pumping gear oil into the gearbox.

My head says the logic is good, but my hearts says NO!!!!! Buy a second pump.
THey're only cheap, so I might buy one anyway, but I wondered if anyone else used these pumps and, if so, do you use them for multiple tasks, or only the one?

[green van man]

I use an oil syringe to top up gearbox ( atf) and transfer box ( hypod 90 ) on the landrover and always wash it out with petrol or thinners and dry between oils. The volatile wash liquids evaporate quickly so little time is lost.

It MAY do no harm to not wash it between oils but IF it does the costs will far exceed the costs of washing or a second pump so why chance it.

Paul.

[Father Ted]

Hadn't thought of running a bit of thinners through.
I agree about costs which is why I've always been so careful. I just didn't want to end up with half a dozen pumps and nowhere to store them.

[anotherv60]

I would recommend another pump, but if you must use the same, try to circulate some of the fresh fluid through the pump before you fill it up - you will need to discard this fluid before filling with a second batch.

ATF and AGO fluids are significantly different, if you have enough contamination the detergent from the ATF will cause your box to run very hot in the bevel gear...but it really depends upon how much contamination you get. The friction modifiers in the ATF will also compete with the extreme pressure additives for the surface, this can cause pitting and failures. However this fails into insignificance if you do it the other way around...goodbye gear box.

Also seals in the transfer box are different - don't know if you might just eat through them in a few weeks/months.

[Father Ted]

Yeah. I'm convinced. I'll buy a hand pump for bevel gear and keep my 12v one for ATF (I'll use that more often).

[luggsey]

I would say keep one pump for clean oil and one for dirty.
When you pump clean oil in just first pump a little clean oil through first.
The tiny contamination amount won't make a jot of difference in the grand scheme of things!

[volvoid]

Auto box holds a lot more than 2 litres.
Still, this technique has merit - far better than doing nothing, always some fresh going in etc

[Father Ted]

Originally Posted by volvoid

Auto box holds a lot more than 2 litres.
Still, this technique has merit - far better than doing nothing, always some fresh going in etc

Yeah, I know.
But the oil isn't that bad to begin with with. This way, every year it gets refreshed rather than a full flush once a lifetime.

Used this method on all my previous auto cars as I tow a caravan with them.