Volvo MD40 Raw Water Cooling

The Volvo MD40 was not putting out as much exhaust H20 as it did / should.

Went for a swim and checked that nothing [e.g. a plastic bag] had been sucked into the engine cooling raw water intake ... all clear.
Checked all hoses ~ all clear / tight / no leaks.
Removed 1" silt / sand from the bottom of the water strainer.
Replaced the water pump impeller ~ it was all there, no vanes missing.

Now, it's worse than before ~ not a drop coming out of the tail pipe!

Any suggestions much appreciated.
Thanks ...

How much of the water pump impeller did you find in place before you replaced it?
If vanes were missing, where did they end up?
Beyond that,over to the Volvo experts.

It is either air locked, sucking air, wrong impeller or the cam is worn or missing. Also check the end plate for grooves. The new impeller is most likely ruined now it doesnt take very long running dry to turn one to dust. Good luck

Volvo MD40 still a no-go

Air locked it may be ~ not sure how to unlock it tho'.
It is the correct impeller and it's not ruined now ~ I checked.
Thanks for all suggestions.

Eclipse said:

Air locked it may be ~ not sure how to unlock it tho'.
It is the correct impeller and it's not ruined now ~ I checked.
Thanks for all suggestions.

Click to expand...

Is the cam in place? This is the part that folds the blades over to push water out of the pump. Check the back plate, pump bore & the inside end of the pump, are they grooved? I leave the back plate loose & open the thru hull when water starts running out tighten the screws down.if water doesn't run out while the screws are loose tighten them down. Take a shop vac & pull water thru the pump with it. The pump should have its prime now & when you fire it up you should have flow. One other thing make sure the thin paper gasket on the back plate is in good shape. Good luck

I'm groping here but is the key in place that drives the impeller? I don't own a Volvo, but how is the pump driven? Is there a mechanical issue with the drive and the pump isn't being driven? Probably a stupid question, but could the feed and output hoses been reversed when reassembled?

In my part of the world we have to winterize our boats so on my MD40 I close the thru hull, take off the inlet hose, elevate it and put another hose inside it that fits snugly. This hose is attached to a 5 gallon pail but you could also just use a funnel. I half fill the the pail with antifreeze but you can just use water. Have someone start the engine. With the pail elevated you will now have a positive head pressure for the water pump and it has to prime. The level in the pail should start to drop immediately. If it doesn't after 10 seconds I would consider that you may have a blockage or a valve closed downstream (hot water heater??). I would systematically start after the engine and pull one hose at a time until you find out at what point you don't have water flow. There aren't that many so it should not take long. Also while the hose is off the thru hull, crack the valve and make sure the ball has not become disengaged from the handle on the valve and is in fact opening, seen that before. Just some thoughts for your consideration.

Capn Craig said:

I'm groping here but is the key in place that drives the impeller? I don't own a Volvo, but how is the pump driven? Is there a mechanical issue with the drive and the pump isn't being driven? Probably a stupid question, but could the feed and output hoses been reversed when reassembled?

Click to expand...

My Volvo has a key that drives the impeller. I've never had to replace it and it's hard to imagine why it would break, but the PO left a spare on the boat.

Eclipse said:

The Volvo MD40 was not putting out as much exhaust H20 as it did / should.

Went for a swim and checked that nothing [e.g. a plastic bag] had been sucked into the engine cooling raw water intake ... all clear.
Checked all hoses ~ all clear / tight / no leaks.
Removed 1" silt / sand from the bottom of the water strainer.
Replaced the water pump impeller ~ it was all there, no vanes missing.

Now, it's worse than before ~ not a drop coming out of the tail pipe!

Any suggestions much appreciated.
Thanks ...

Click to expand...

You did check to see that the seacock is open, right? You closed it to change the impeller, did you remember to open it afterward?

Capn Craig said:

I'm groping here but is the key in place that drives the impeller?

Click to expand...

Gentlemen,

I removed the water heater from the equation / hooked unblocked in/out hoses together + ran an unblocked hose direct from the open seacock to the engine + primed pump + all hoses with H2O.

A little better than before but not for long ... ever-so-slight grey/white smoke and some bubbly water as I used washing up liquid to lubricate the new impeller when installing ~ out the tail pipe!

Engine starts up 1st time every time and runs smoothly in and out of gear ~ I shut it down the instant I ascertain the situation.

Looks like it's time to call in the professionals!

Thanks to all ...

One suggestion: this sounds like it could be a leak in the suction hose to the pump. This would cause the hose to admit air, which would cause the pump to not be able to suck in water.

Scott Welch
Island Eagle

As some [not many] of the hoses are the originals from when the engine was installed in 1996, replacing them all is long overdue and next on the list.

Also, will check the mixing elbow for carbon buildup blocking the outflow.

If nothing else, boating is an education ~ in more ways than one.
I have learned, I spend more time [and money] on maintenance ~ than on the water!

Can you disconnect the far end of the Raw water pump outlet hose and run it to a bucket to see if it is pumping. That way you'll be able dicard the pump and it's feed as causing the problem. If it is pumping well check it where it enters the heat exchanger then the output of the heat exchanger and so on.
Steve

Eclipse said:

Gentlemen,

I removed the water heater from the equation / hooked unblocked in/out hoses together + ran an unblocked hose direct from the open seacock to the engine + primed pump + all hoses with H2O.

A little better than before but not for long ... ever-so-slight grey/white smoke and some bubbly water as I used washing up liquid to lubricate the new impeller when installing ~ out the tail pipe!

Engine starts up 1st time every time and runs smoothly in and out of gear ~ I shut it down the instant I ascertain the situation.

Looks like it's time to call in the professionals!

Thanks to all ...

Click to expand...

Please let us know what you find in any event. May be a learning for some of us with similar equipment. Good luck and hope it's a cheap fix.

Eclipse,
I'd try an extended version of the LaBomba winterization. Try and list some facts ... just what you can find out. Mainly where can the water go and where IS it going. Use the LaBomba bucket system (I do that too) and make a list of what is and isn't happening. If it's a remote pump like I've got it would be easy to unhook the discharge hose, rig the intake hose into a bucket w water in and try. But w a pump built into the engine the discharge may not be that assessable. It may too depending on the engine system design. But it goes somewhere. Follow the water.

The sand in your strainer is could be a hint as to what the problem is. Is it sand too small to go through the strainer? If the sand can pass through the strainer follow the sand. Also some of the sand (the bigger granules) may be in the strainer but most of the sand if it's fine could be downstream of the strainer. At any rate just following the route of water flow should reveal the problem.

You can probably find the problem w logic and then decide if you should call the mechanic to fix it. It is often said that the most important mechanical knowledge one can have is knowing when to call and when not to call the higher help.

The impeller has been replaced but is it turning?

The key that drives the impeller may be broken.

Take the cover off the pump, "bump" the engine without starting it and see if the impeller turns.

Am working solo on the problem at present [while the wife is away] however ~ if an airlock is possible, I may have cured it.

I closed the seacock and, having checked and primed all the hoses once more, fired up the engine and, at the 1st splash of H2O out of the exhaust, immediately opened the seacock ... bingo, back to normal [I hope] ... we'll see how long it lasts.

Many thanks for all the suggestions.