Allison Transmissions, where is the oil going?

[zigzag930]

After some more thinking about this... I am refining my thoughts on what might be going on.

1) If the rear main seal of the engine was leaking oil into the transmission, the oil in the transmission would not be clear (it is) and would be darker like the engine oil. So I don't think the rear seal is the problem, unless the transmission oil is being forced into the engine. Don't see that as likely, but perhaps.

2) If the transmission oil cooler was leaking, I'd think I'd see water in my transmission or some milky oil. Now thinking the transmission cooler less likely culprit.

3) Transmission oil pump??? Maybe a seal on the back side of the Hydreco transmission oil pump is worn. Might that allow oil into the engine? I'm not sure about that, but maybe worth investigating. I did recently notice that there is a slight leak on the front side of the pump. Called a company (Acadia Marine) that repairs them and was told that is a common issue with these pumps. I'll call them again tomorrow and ask about the engine side seal maybe causing this problem.

[SKYCHENEY]

Trans oil pressure is much higher than the water in the heat exchager so oil would leak out and not water in.

[rwaldrop13]

Rob, I'm not familiar with the intercooler. Would oil between the engine and transmission mix there without water getting into them?

I was told the capillary tubes are joined/fastened together and the joints can create bleedovers.

[zigzag930]

After speaking with another trusted Forum member last night and then to Brian at Arcadia Marine, I'm 99% certain the issue is the Hydreco transmission pump.

So now, I just need to decide if I want to rebuild them myself or send them out. Looks pretty easy, so I may go that route.

Either way, I'll update the forum with the results once I know for sure