V drive overheat - what to do about it

Whitelighter

Whitelighter

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Watching the SQ58 displacement thread it reminded me of a problem I have with Seralia.
The boat has a V drive set up, so engines mounted 'backwards' with the shaft returned through a reversing box.

When running at displacement speed after a couple of hours I get a overheat alarm (usually on port first but can happen on either) indicating the reservsing box is getting hot. The water cooling for the V drive is passive force - a pick up in the hull which I guess requires speed for sufficient pressure to keep the flow going. Ive checked and cleared the filters and they seem fine, but I guess after 22 years its possible there may be some build up in the pipe? Now it may be that these were never designed to facilitate slow speed running but I'm surprised if the cant cope with pootling.

Any suggestions how to clean the pipes? and with what. Without a pump how do I force the cleaner through.

Also, is it reasonable for the boxes to need that much cooling or should I be looking at another issue. Popping the boat up onto the plane for 20 minutes cures the alarm for another couple of hours but that's going to be a pain on a night passage.
 
Is there a sea water heat exchanger ? If not how are they exactly cooled by the sea?

If so? ---passive pressure for the water you say ,but the Oil?--is there a pump .? If so then this side may be failing ?
So plenty of water at Pootle as designed but the oil flows down maybe =overheat .
Or water pipe(s) need a clean out along with the core in the HE
Acid s best any brick cleaner or similiar
 
+1 on what Portofino says,

Also, assuming you have checked level of oil, are you sure it's the right type of oil :rolleyes:
Maybe it's thicker than it needs to be and is only fine when working at higher revs/temps as it thins down and does its thing better, just saying...

Time to replace and measure how much you add for good measure (and a method to check if the indicators are fine.

cheers

V.
 
Good points. Oil will be drained and changed before the start of the season so it will be the correct type and volume.
Don't know how the heat is exchanged - not connected to the engine (about 6ft away) so either its own pump (though very small casing) or I guess circulation just by the gears turning.

They do I think have dipsticks so I'll check those
 
Jez

My money is on a gradual build up of marine growth restricting the passages, so with low flow the cooling is simply too low.

Not sure what the answer is with the boat afloat, but a decent descaler might be the answer, e.g. rydlyme.
 
If there is no raw water pump can you find the intake and exit sea cocks?

Shove slightly oversized pipes into both returning to a bucket, bilge pump on one hose, let it rip for a few hours.

a few unknowns in my idea I appreciate :)
 
Whitelighter said:
When running at displacement speed after a couple of hours I get a overheat alarm (usually on port first but can happen on either) indicating the reservsing box is getting hot.
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The same thing used to happen with my Ferretti 46 which also had V drive gearboxes and the cure was the same - speed up. I dont remember there being any kind of heat exchanger on my V drive gearboxes on my F46 (although there are on my F630). I think the best you can do is change the oil, check that the seawater intake and pipework is clean and possibly check that the sensors are not telling lies
 
Just found a picture of the V drive on my F46. No heat exchanger as far as I can see

DSCN0681001-1.jpg
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Hi Mike. Yep, that looks identical to the v drive boxes on Seralia.
Interesting you had the same issue - the universal warning light is a bit annoying and one of my projects is to replace the electric DD gauges at the lower helm with more reliable mechanical temp/pressure/rpm units. I might see if I can add oil temp gauges to the v drive boxes as well
 
Not up on that layout, but is that a hull fitting with water strainer responsible for cooling the gearbox? if so I would imagine that there would be a suction pump in the unit to pull water through for cooling, also the outlet appears to be going towards the exhaust elbow, Take the cap off the strainer and clean out the bowl, remove the pipes and clear any blockages, Then run her up in gear and see how much sea water comes out the outlet before you refix to exhaust elbow.
 
Yes the hull fitting with the strainer is the intake, though the black pipe going towards to exhaust elbow is not the out let. The outlet you can see is the same type of clear pipe leaving outboard via another sea cock
 
Whitelighter said:
Yes the hull fitting with the strainer is the intake, though the black pipe going towards to exhaust elbow is not the out let. The outlet you can see is the same type of clear pipe leaving outboard via another sea cock
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I would hope that the casing has a water jacket built in and the water is forced through it, cannot see such an expensive looking bit of kit as that being left to look after itself, what make is it? surely there is a "book" on it. I can appreciate not much water if any going around when stationary and in neutral but underway a pump would be a great help.
 
omega2 said:
Not up on that layout, but is that a hull fitting with water strainer responsible for cooling the gearbox? if so I would imagine that there would be a suction pump in the unit to pull water through for cooling, also the outlet appears to be going towards the exhaust elbow, Take the cap off the strainer and clean out the bowl, remove the pipes and clear any blockages, Then run her up in gear and see how much sea water comes out the outlet before you refix to exhaust elbow.
Click to expand...

No you can just see the outlet going to a seacock on the other side of the gearbox. I stand to be corrected but I think the pipe coming out of the top of the box is just an overflow pipe in case of blockage in the outlet pipe. The exhaust pipe you can see is actually the generator exhaust. Also again AFAIK there is no pump in the gearbox. If there is I certainly didnt do any servicing on it in 4 yrs of owning the boat

If Whitelighter's gearboxes are set up in the same way, maybe one way to check the water flow through the gearbox would be to shut the outlet seacock and see how much water is coming out of the overflow pipe at various speeds. As for cleaning the internal pipework in the gearbox maybe shutting both seacocks and filling the pipework with Rydlyme or similar might help
 
omega2 said:
I would hope that the casing has a water jacket built in and the water is forced through it, cannot see such an expensive looking bit of kit as that being left to look after itself, what make is it? surely there is a "book" on it. I can appreciate not much water if any going around when stationary and in neutral but underway a pump would be a great help.
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I do have a pretty comprehesive manual from Ferretti for the boat (albeit in italian) but the section on the V drives just gives the type and quantity of oil required and the oil change schedule. No mention of a pump or impellers to change etc
 
a quick google reveals that V drives like yours have a water jacket around the actual gears. If it works OK when planing it looks like the water flow is a bit marginal. I would take all the cooling hoses off and fittings and give it a good clean. If that's not enough then its either strip the whole thing or rydlyme the gearbox via the cooling ports. Hopefully its just got some gunge in the pick up pipe. Also is the gearbox actually completely or partially below the water line? in which case it will just fill with water anyway, relying on some sort of scoop or hull shape to create a small pressure difference to get water to circulate.
 
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Deleted User said:
It has to be otherwise the seawater coolant wouldnt get into it:)
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Alright. I learnt a long time ago that making definitive statements on here bites you on the arse :)

I did wonder about fitting some in line electric pumps which I could turn on when the overheat warning sounds as an alternative to just speeding up - though perhaps this is a bit heath robinson and doesnt really resolve the issue
 
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