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Old 23-11-2012, 17:11   #1
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Header Tank To Eliminate Saildrive Salt Water Intrusion

Sometime ago I saw a really cool saildrive modification on this site that I'm considering doing. I am hoping to get some good input or reasoning as to why I shouldn't do it, before I do. Hopefully the guy that thought of it and posted it, will tell us how it worked out in the long run.

Next to regularly cleaning the raw water intake channels in the saildrive, the next worst thing is when the lower seals fail and sea water mixes in with the oil. Necessitating immediately hauling the boat to replace the seals.

I saw a blog here a few years ago where someone installed a radiator overflow plastic tank just above the water line and ran a hose from the tank to a male hose fitting that replaced the dip stick on top of the saildrive unit. The head pressure from the 90 weight oil in the overflow tank, mounted just above the water line would STOP the seawater from intruding into the failed seal and conversely send 90 weight oil out, before the seawater came in. Given the viscosity of the oil, very little if any would ever leak out, but will block the seawater from EVER coming in.

Seems like a "No Drainer" to me and very inexpensive to do. Much less money than one haul of the boat for an emergency seal replacement.

Comments????
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Old 23-11-2012, 22:22   #2
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

I may be the gullty party. At least I hadn't heard of anyone doing this before I did.

Still works for me. Easier to check/add oil as well.

I had ordered radiator over flow tanks, fretting over the high cost. But when they didn't arrive as promised, I cancelled, and made tanks out of Lucas injector cleaner bottles. Drilled a hole in the fill cap and pressed a 1/4 in. ss tube in it down to oil level hight. Threaded a pinch valve on the vinyl tube (which I replace each haulout). The caps ere made out of the outer portion of a gallon antifreeze cap.
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Old 24-11-2012, 00:03   #3
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

I worked on an island and we used trucks to convey passengers driving the trucks to 3ft deep at times, the Differentials were set up with small header tanks exactly as you suggest and it worked a treat.

Some might say the lip seal won't tolerate pressure and leak because of the pressure from the header.

More to the contrary they may only leak when you slip the boat as there is no seawater pressure on the outside BUT that's of no consequence really.

I like the idea, as i said it worked on the trucks we never saw any water in the diffs...
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Old 24-11-2012, 07:55   #4
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

I am going to do this as well. I don't really think that the pressure from the header tank makes a big difference. The reason it works is because it vents the gear case. The seal on my starboard saildrive has been leaking again. When you run it hard the heat builds up the pressure inside the the saildrive. It is when it is cooling that it develops a powerful suction that can pull the water in if the seal isn't perfect. If I could remember to loosen the cap after running it hot it would not leak. I am thinking of using a length of clear hose adapted to the dipstick threads. I will attach it to a high point and put some kind of vent filter over it. This should work unless there is a tendency for the oil to spurt out in which case I would go ahead and install some sort of reservoir. I have also been trying to find a cheaper source for the Volvo seals which are $30. apiece. (it uses two of these back to back) The problem is that the rubber part is Viton. The only comparable seals I could find are over $20. but are a little thinner. (the thinner seal might be a good thing if your shaft is starting to groove because it would contact a different spot on the shaft) I thought I would be able to find some seals for $5. or $6. but decided not to risk it but in a pinch I think that as long as it had a stainless spring that it wouldn't have to be Viton and you could use seals from an auto parts store. Comments?
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Old 24-11-2012, 08:36   #5
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

Mercruiser has used a system like this for quite a while on their bravo drives , clear bottle so one can see the fluid level quicky
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Old 29-05-2016, 09:02   #6
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

I know this is an old thread but it has served me well and I thought others might have trouble sourcing the parts.

Having seen this thread, I decided to install an oil header tank for my Volvo MS25S Saildrive. The difficult bit is finding a suitable plug to replace the dipstick. Turns out Judd engineering had just the right part.Go to https://www.juddracing.com/en/ktm-oi...-breather-2972 and select the M24 x 3mm KTL breather plug.

The header tank is a mini-moto fuel tank - 1 litre from eBay and the fuel tap is also from eBay.

Works just fine for me.
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Old 30-05-2016, 04:29   #7
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

a brilliant idea!
(& apparently it doesn't harm the saildrive that it is chockablock full of oil...this would have been my concern...)
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Old 30-05-2016, 05:10   #8
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

Greetings and welcome aboard the CF, Chris.
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Old 30-05-2016, 10:21   #9
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

A good write-up on the subject here...

Sail Drives
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Old 31-05-2016, 11:47   #10
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

I just ordered 2 of these to do my sail drives. Dorman - 603-001 - Universal
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Old 31-05-2016, 20:44   #11
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

Quote:
Originally Posted by tunnelvision View Post
I just ordered 2 of these to do my sail drives. Dorman - 603-001 - Universal
Do these tanks have an overflow outlet? If they are completely sealed they might not work as suggested. The idea as I understand it is that as the oil cools and contracts it creates a vaccum which helps the sea water to enter. A hole drilled in the cap would alleviate the problem.

Good find though. I think I'll order two also.
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Old 15-06-2016, 07:57   #12
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

I noticed on several occasions when I unscrewed the filler to check the oil air hissed in/out, also this time when I hauled out there was some water in the oil. The shaft was deeply scored and there was water staining on the shaft so no doubt it was leaking. I cleaned the shaft and installed some double lipped seals (5 each) these sealed on an area on the shaft not worn and were considerably cheaper. I also added a vent to the saildrive and put the end of the pipe in a small plastic bottle to vent. Total cost 15.
this was on an Volvo s130 all has been well since.
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Old 16-06-2016, 00:31   #13
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

We have the Yanmar SD20s which injested sea water while the boat was in charter along with many other boats. The saildrive seals were replaced every year. The operating company took this up with Yanmar who advised that the problem was lack of venting and to keep the oil level on the minimum mark. Since then, no more problems.
It seems the problem is that when in us the oil gets hot and expands, upon stopping the oil cools down and if it cannot vent, perhaps because the oil level has risen, tends to suck in seawater.
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Old 16-06-2016, 13:12   #14
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

To give you some idea, the oil vents into and half fills a 125cc bottle, as the tube is in the bottom in drains back in when cold. If anyone is interested the shaft seals i used were imperial sized - yup I though they would be metric too!
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Old 16-06-2016, 14:56   #15
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Re: Header Tank To Eliminate Saildrive Salt Water Intrusion

Quote:
Originally Posted by Thumbs Up View Post
The problem is that the rubber part is Viton. The only comparable seals I could find are over $20. but are a little thinner. (the thinner seal might be a good thing if your shaft is starting to groove because it would contact a different spot on the shaft) I thought I would be able to find some seals for $5. or $6. but decided not to risk it but in a pinch I think that as long as it had a stainless spring that it wouldn't have to be Viton and you could use seals from an auto parts store. Comments?
You can buy thin SS sleaves which are driven onto the shafts to cover the grooves and present a smooth surface to the seals.

If the available seals have carbon steel springs, remove the spring and replace it with an appropriately sized O ring.
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