Coolant leak into transmission - a few questions

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James P
Oil Injector
Posts: 582
Joined: Mon Mar 11, 2013 10:47 am
Location: Sydney, Australia

Coolant leak into transmission - a few questions

Post by James P »

Only 200km on my rebuilt engine and there's coolant in the gearbox oil :( . It must have happened somewhere between the 100km and about 180km point, because the oil looked clear up to the earlier mark. At around 180km, it looked cloudy. On completion of the journey and removing the radiator cap, the coolant level in the radiator had dropped. The coolant I drained did not smell any different to the new coolant remaining in the container from which I had filled the radiator, so I think I can discount any problems with head or base gaskets leaking.
Just to make sure I was correctly diagnosing the problem, I put a small amount of new coolant into a jar of new gearbox oil. The result looked nearly identical to the liquid I had just drained from the gearbox.

On stripping the side casing and water pump housing, all parts still look fine - there is no discernible damage to the impeller shaft, the mechanical seal or the oil seal. There is still perceptible resistance felt when the impeller shaft is inserted into the oil seal (it was lubricated on assembly), so the oil seal is not "blown". The impeller was still tightly fixed to the shaft, as I had put Loctite on the nut when assembling.
Both the oil seal and mechanical seal assembly were new genuine items (with the correct part numbers) fitted when the engine was rebuilt. They now look exactly the same as they did when fitted - nothing has been displaced. There are obviously some wearing-in marks on the sealing surfaces of the mechanical seal, but the surfaces have no chips or pits.

Despite the lack of apparent cause, I may have made an error when assembling the pump drive. I fitted the mechanical seal first, followed by the oil seal and then the ball bearing. It appears that this led to obstruction of the drain passage behind the mechanical seal.
The workshop manual implies that the parts should be fitted in the opposite order (i.e. bearing, then oil seal, then mechanical seal). Even though the oil seal ended up too far "outwards" (only by 1mm), I'm struggling to see how this caused coolant to leak through the oil seal. Is there any other point on the engine unit where coolant may leak into the transmission?? :?:

I've taken some measurements of the "tunnel" in the side casing and the components which fit into it. When correctly assembled, it seems that only 1mm of the 4mm diameter coolant drain passage will be exposed - is that enough?? :?:
The manual states "Do not block the coolant draining outlet passage with the mechanical seal by pressing it too deep into the right engine cover" - how deep is too deep?? :?: As far as I can tell, the mechanical seal body must be fully seated to prevent it later being displaced (by heat, vibration and spring pressure) and possibly causing the pump impeller to come loose and the mechanical seal to leak.
The depth of the mechanical seal body is 8mm, whereas the edge of the coolant drain passage is only 6mm from the mechanical seal seat in the casing. Thus, when correctly seated, the mechanical seal body obscures half of the coolant drain passage - is that OK? :?:

I don't want to simply reassemble the parts, only to find the same thing happens again (even though I will assemble the pump drive in the correct order this time!). Can anyone offer any advice?

Thanks & regards,
James
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