D6 Curious Quirk

[oldgit]

Roped in to help an owner bring back to its home moorings a boat with a pair of early D6 engines.
Boat still in slings but in the water.
Checking for leaks and as both impellers changed want some cooling water visible in filters..
One Impeller sucks in water for a minute and then stops.
One, the one hidden away and virtually impossible to see refuses point blank to suck anything.
Eventually remove the easy to get to casting to reveal an impeller, right shape and size and vanes all correctly positioned, "o" ring in position and with dab of instant gasket no chance of a leak.
Still no water.
Tide is now ebbing and its either boat back onto hard or tugboat off to pontoon.
Boat taken off to pontoon.
Much head scratching and a cold beer.
Remove filter cap ,start engine and you drown. impeller working 101%,.............. lid back on and Nada.
Having changed not a few impellors over the centuries, both at leisure and under duress cannot ever recall any engine/pump/impeller combination ever not instantly pumping water from the word go.
The boat had been out of the water for around 2/3 weeks for remedial "work", was this a clue, about to pack it in and go home.
One last go.
Water point nearby. Spend ages filling water filter with hose only to watch it drain away but it then remains full and only very slowly drops. put filter lid on super quick and start engines.
Yippee problem sorted.
Repeat with other engine and leave to tick over with fingers firmly crossed probably a lot longer then needed.
Make sure anchor is working and head back home.
Air lock somewhere ?

Update skipper has just started engines again this morning..... Exactly the same problem......Suggestions welcome.

 

[volvopaul]

Roped in to help an owner bring back to its home moorings a boat with a pair of early D6 engines.
Boat still in slings but in the water.
Checking for leaks and as both impellers changed want some cooling water visible in filters..
One Impeller sucks in water for a minute and then stops.
One, the one hidden away and virtually impossible to see refuses point blank to suck anything.
Eventually remove the easy to get to casting to reveal an impeller, right shape and size and vanes all correctly positioned, "o" ring in position and with dab of instant gasket no chance of a leak.
Still no water.
Tide is now ebbing and its either boat back onto hard or tugboat off to pontoon.
Boat taken off to pontoon.
Much head scratching and a cold beer.
Remove filter cap ,start engine and you drown. impeller working 101%,.............. lid back on and Nada.
Having changed not a few impellors over the centuries, both at leisure and under duress cannot ever recall any engine/pump/impeller combination ever not instantly pumping water from the word go.
The boat had been out of the water for around 2/3 weeks for remedial "work", was this a clue, about to pack it in and go home.
One last go.
Water point nearby. Spend ages filling water filter with hose only to watch it drain away but it then remains full and only very slowly drops. put filter lid on super quick and start engines.
Yippee problem sorted.
Repeat with other engine and leave to tick over with fingers firmly crossed probably a lot longer then needed.
Make sure anchor is working and head back home.
Air lock somewhere ?

Update skipper has just started engines again this morning..... Exactly the same problem......Suggestions welcome.

Shaft drive ? If so possible exhaust back pressure not allowing water to flow freely .

 

[roa312]

Remove filter cap ,start engine and you drown. impeller working 101%,.............. lid back on and Nada.

The line above stood out to me - I have a couple of D6s myself (370hp version), and I’ve noticed that once the air is out of the raw water strainer and everything’s sealed up (which is immediately after engine startup), you often don’t see any water movement in the strainer at all, even though the system is working. Without any air bubbles, sea weed stuff or turbulence to make the flow visible, you really can't see water flow through the lid. This may be totally irrelevant to your problem, but I just wanted to mention - easy to check from the exhaust water at idle (at least if not outdrives).

Maybe you could try briefly loosening the strainer cap after shutdown: if water is under suction or spurts slightly, probably the system is working as intended?

 

[julians]

The line above stood out to me - I have a couple of D6s myself (370hp version), and I’ve noticed that once the air is out of the raw water strainer and everything’s sealed up (which is immediately after engine startup), you often don’t see any water movement in the strainer at all, even though the system is working. Without any air bubbles, sea weed stuff or turbulence to make the flow visible, you really can't see water flow through the lid. This may be totally irrelevant to your problem, but I just wanted to mention - easy to check from the exhaust water at idle (at least if not outdrives).

Maybe you could try briefly loosening the strainer cap after shutdown: if water is under suction or spurts slightly, probably the system is working as intended?

Yep, same on d4, you can't tell by looking through the perspex strainer lid that water is flowing,it just looks empty, but water is flowing.

Could it have been that?

 

[oldgit]

Shaft drive ? If so possible exhaust back pressure not allowing water to flow freely .

" have a couple of D6s myself (370hp version), and I’ve noticed that once the air is out of the raw water strainer and everything’s sealed up (which is immediately after engine startup), you often don’t see any water movement in the strainer at all, even though the system is working."

I wonder !

Complete replacement IPS leg just fitted, exhaust of course fully under water.
Both cooling water valves definately fully open.
Have split hoses as far back as riser and loads of cooling water that far back...enough to thoroughly soak the unawary at least.
Must confess did shut down engine as soon as no flow noticed btu perhaps should have left until gauge temp went nuts ?
The standard test of feeling the impeller casing revealed it was not getting hot fast the usual hint that water is not lubricating/cooling the vanes

 

[sap_2000]

Spend ages filling water filter with hose only to watch it drain away but it then remains full and only very slowly drops. put filter lid on super quick and start engines.
Yippee problem sorted.

The D4 and D6 up to 2013 in stern drive or IPS configuration had the strainer after the impeller pump. After that they finally moved the strainer to after the pump.
After some time on the hard, the pump housing dries and its quite common that it doesn't draw water on its own unless the impeller is lubed OR you fill the the filter and fill the water down the inlet that leads down to the impeller pump.
Then as you discovered, the problem is solved.
Here, most boats spend 6-8 motnths on the hard and often put back in in relatively cold temperatures. So priming of the pump, or re-install the impeller just before launch is recommended. Silicone spray or silicone oil works great if you not have the VP glycerine bag that comes with a new impeller at hand...

 

[oldgit]

Awaiting the wisdom of the folks who installed the new IPS leg as to next step to find out if there is even a problem. Shut till Monday.

 

[NorthUp]

If your seawater strainer has a clear top place a table tennis ball in the basket to see if there is water flowing.

 

[Andyroonot]

" have a couple of D6s myself (370hp version), and I’ve noticed that once the air is out of the raw water strainer and everything’s sealed up (which is immediately after engine startup), you often don’t see any water movement in the strainer at all, even though the system is working."

I wonder !

Complete replacement IPS leg just fitted, exhaust of course fully under water.
Both cooling water valves definately fully open.
Have split hoses as far back as riser and loads of cooling water that far back...enough to thoroughly soak the unawary at least.
Must confess did shut down engine as soon as no flow noticed btu perhaps should have left until gauge temp went nuts ?
The standard test of feeling the impeller casing revealed it was not getting hot fast the usual hint that water is not lubricating/cooling the vanes

As suggested, these can be difficult to determine if there is water flowing without any bubbles or weed bobbing about.

The face-plate test is a good one and so given that you’ve done that plus removed plenty of hoses and found they contain water, I really can’t see that there is an issue

The change of drive (I think it was actually a lower leg that was replaced but required the whole drive to be dropped out to do the work) shouldn’t have had any bearing on the water flow, especially as the two valves are open as you have confirmed.

Is the exhaust getting hot? This has the seawater flowing into it after the engine and so similar to the impeller face-plate touch test, if that’s not getting stupidly hot then it’s probably flowing just fine

 

[oldgit]

Today..............................
Run up both engines brief spurt of visible water flow on start up in the only filter you can actually see.
No water visably moving around in filter after start up.

Run up both engines for 5 mins, then in gear to approx 1000rpm and wait.

Temps slowly rise and after about 20 mins both engine temps on dash gauges up to 75-85 C.
Both impellor casings cold and measure at about 30C.
Intercoolers etc cold and both around 30C,
Both risers around 50C , hot , but skin stays on your fingers.
Turbos about the same .

Surely there has to be water going through the cooling system....

 

[Andyroonot]

Today..............................
Run up both engines brief spurt of visible water flow on start up in the only filter you can actually see.
No water visably moving around in filter after start up.

Run up both engines for 5 mins, then in gear to approx 1000rpm and wait.

Temps slowly rise and after about 20 mins both engine temps on dash gauges up to 75-85 C.
Both impellor casings cold and measure at about 30C.
Intercoolers etc cold and both around 30C,
Both risers around 50C , hot , but skin stays on your fingers.
Turbos about the same .

Surely there has to be water going through the cooling system....

All sounds good to me!

 

[julians]

Today..............................
Run up both engines brief spurt of visible water flow on start up in the only filter you can actually see.
No water visably moving around in filter after start up.

Run up both engines for 5 mins, then in gear to approx 1000rpm and wait.

Temps slowly rise and after about 20 mins both engine temps on dash gauges up to 75-85 C.
Both impellor casings cold and measure at about 30C.
Intercoolers etc cold and both around 30C,
Both risers around 50C , hot , but skin stays on your fingers.
Turbos about the same .

Surely there has to be water going through the cooling system....

Sounds fine tome. You really cannot see any water flowing in the filter baskets on the d4 (so I presume it's same on the d6), it just looks like they're empty, but they aren't, there is just no air at all to create any kind of turbulence. a ping pong ball in the basket would tell you for certain.

 

[oldgit]

Going to road test on Tuesday.
The choice we both go on his boat.......................
Or
OG follows behind in his reliable and simple shaft driven boat and a pair of simple" fix with a hammer Yanmars" plus decent length of warp to tow the IPS boat back.

Go on you know you all want to comment

 

[madabouttheboat]

Going to road test on Tuesday.
The choice we both go on his boat.......................
Or
OG follows behind in his reliable and simple shaft driven boat and a pair of simple" fix with a hammer Yanmars" plus decent length of warp to tow the IPS boat back.

Go on you know you all want to comment

Option 3: Old git's Yanmars die and he has to be towed back by a Volvo powered IPS boat. Oh the embarrassment.

 

[oldgit]

Option 3: Old git's Yanmars die and he has to be towed back by a Volvo powered IPS boat. Oh the embarrassment.

Those little Yanmars do rather well when it comes to towing boats with Volvo Penta engines
Modesty prevents one mentioning which boat is doing the towing.