sterntube header tank

I think you are asking if there will be an oil flow back to the header tank after the oil has gone through the stern tube - if you haven't got a pump for the return oil the answer is no! From my recollection stern tube oil is sacrificial - you don't want to re-use it in case it has been contaminated with seawater, unless you have what might be called a sophisticated oil recovery system.

You should have sightglass on your header tank to monitor the oil level, both in port, and more importantly at sea to record your consumption and pre-empt any defects. The other thing that puzzles me is your stern tube oil, OMD113 - I think the viscosity is questionable for that purpose.

Why do you have high bearing temperature? it is a normal practice to use some of the engine salt water cooling to be directed into the bearing and stern tube, if working properly it should keep the temp at a reasonable level.

The oil in the bearing should sit between seals with a dual reversed seals between the oil and water to reduce oil loss.

Your problem with high temp. would point to shaft misalignment, or bearing wear, Do you also have vibration? I used to sail with a friend on his boat, the engine was a Badouin 4 cyl. diesel, it generated a lot of vibration as an engine in itself, but we also experienced vibration from the shaft, which was approx. 4inch. dia,. driving a 3ft. prop. coupled to a 3-1 gearbox. We dismantled the shaft and bearings, and had new bearings made, having first remettled the shaft, and machined back to size, everything was reassembled, and religned to the gearbox coupling, We drained the old oil out of the lub. oil header tank and refilled with engine oil, the shaft ran cooler under way, but there was heat there, which we called hand hot, or running heat. The oil system was a total loss system, the inner gland seal stopped the oil and water leaking into the boat, the outside was taken care of by a rubber seal that turned with the shaft if I remember correctly, and made contact with a machined face on the stern tube, a sort of convex shape with the the lips facing inwards. My friend used to use old engine oil in the header tank for reasons of economy, but I weaned him off that, in favour of something more substantial, but my choice would have been a Vickers oil made especially for the job. You also ask about having a return to the header tank, as someone else has pointed out, you can't get a return without a circulating pump, as he also said you don't want to risk contamination with salt water, In all my years as an installation fitter, working on various boats, from small things to quite large engine powers up to 2,500 hp MTB's, I have never seen a pumped system for the stern gear. Hope this helps.

Your first problem could be using OMD(Oil Mineral Detergent) oils which were generally used in diesel engine crankcases whereas stern tube lubricants are compounded mineral oils with additives like Viscosity Index Improvers,emulsifiers and corrosion inhibitors. If you have a leak in your outboard seal water will obviously enter the stern tube and combine or form an emulsion which will continue to lubricate the bearing and prevent corrosion.

You should not only have a reservoir but also a circulating pump because it is highly unlikely that you would get thermo-syphoning, therefore no oil cooling, you may also need a larger reservoir or an oil cooler (make sure it is sized). The return line can be slightly larger than the supply line.

DO NOT use any plastic piping in machinery spaces because if you have a fire...... you will increase the fuel load.

Yes Mobi -

Vickers produce an emulsifying oil called Neox that's been around for 100 years. Since 2003 they have produced another oil that is environmentaly friendly called Hydrox Bio.

Hi mixit,

that certainly is very apt for hydraulic oils, you will find now that most oil companies produce a specific stern tube oil, the same way as most packing manufacturers make a specific stern tube packing.

Note:- I am not saying that conventionally packed stern tubes are oil lubricated, they are not.

Thanks "mixit" for the Vickers type oil "Neox" reminder, It's been so many years since I worked with the stuff, not quite the 100 you mentioned it's been around tho', lets say half of that! bangorjohn.