no water! - it isnt the impeller

stu9000

stu9000

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Hi

Id appreciate some help with this as I've been doing battle for several days now.

The engine seemed fine last season but this year no coolant water is coming out of the exhaust.
The engine starts ok but not even a trickle is coming out of the exhaust!

Volvoo MD7A engine
Sea water cooled
Sail drive leg
There is no strainer box and the water comes in from the leg.
Yes the tap was turned on.
I also removed the hose and ran it from a bucket of water.

I assumed it wasn't priming and suspected the impeller and or the water pump plate which was somewhat worn.
New plate and I am now expert at removal and replacement of impeller.

Then I thought the air seal wasn't good enough on the push fit water in pipe to the water pump.
I continued to wonder about this until i pulled up on the pump 'water-out' pipe.
Bubbles and air escaped from the join under pressure suggesting the pump WAS doing its job but that something else down stream was blocking the water flow.

So I took a deep breath and got out the socket set.
I removed the thermostat housing.
This allowed me to test the water pump and impeller. I ran the engine and confirmed the water pump DOES push water through to this point. There was quite a lot of salt deposit and debris flushed out.

The pics below show the engine and themostat housing removed.

engine4.jpg

engine1.jpg

engine2.jpg

I cant see anything resembling a working thermostat.
Images of a replacement show a spring. I assume this has completely corroded away. But even without this thermostat working water should be able to get through the engine to the exhaust by one route or another. Ill fit a new unit at some point but I dont think this is the problem.

What has got me stumped is the COMPLETE absence of water coming out of the exhaust.
Not even a trickle.

I guess the next stage is to remove the exhaust manifold coolant housing.
Im on board now so Im going to get to it!

I am out of my comfort zone at this point and an worried about causing as many problems as I solve so any advice would be gratefully received.

S
 
stu9000 said:
Hi

Id appreciate some help with this as I've been doing battle for several days now.

The engine seemed fine last season but this year no coolant water is coming out of the exhaust.
The engine starts ok but not even a trickle is coming out of the exhaust!

Volvoo MD7A engine
Sea water cooled
Sail drive leg


What has got me stumped is the COMPLETE absence of water coming out of the exhaust.
Not even a trickle.

I

I am out of my comfort zone at this point and an worried about causing as many problems as I solve so any advice would be gratefully received.

S
Click to expand...

Water injection point into the exhaust outlet bend blocked ???? You dont seem to have mentioned this .


5691.jpg
Hose #7 may incorporate an anti-siphon loop and " vacuum valve"
 
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You are not going to damage anything - these engines are bullet proof, sort of.

Try removal of the exhaust manifold, Item # 1 in Vic's diagram - check for flow (or blockage). We had ours blocked to a 3mm diameter (approx) hole - and it would not take much debris to block it completely.

Simply undo the 4 nuts on the studs, leaving the exhaust hose attached (as I have found it very difficult to remove). You will then be able to see if there is any blockage. You might need to replace the manifold to get the hose off.

Jonathan
 
Try checking for flow at pipe 7 maybe extended to include antisyphon valve
Be aware that running engine without water to exhaust hose will cause it to delaminate May also cause water lock damage
 
Gulp!
It looks like the whole thing is blocked!

Vic, you mentioned the "water injection point into the exhaust outlet bend".
Im not sure where this is.
As I understand it the water comes in via the thermostat.
It turns right through the small (currently blocked) holes, through the engine block and back into the exhaust duct.
Im a bit unclear on the exact re entry point as it us all utterly clogged.
engine10.jpg

engine6.jpg



Im off to get some brick cleaner which i hope will sort the coolent unit i have taken off the engine.

The engine block is going to be more of an issue.
Ill wiggle about with some wire.
If i can get some flow through is it appropriate to mix some brick cleaner into the water and run it through the engine?
Id appreciate some advice on what liquid I can use to clear out the engine side pipes.

Thanks all
 
stu9000 said:
Gulp!
It looks like the whole thing is blocked!

Vic, you mentioned the "water injection point into the exhaust outlet bend".
Im not sure where this is.
As I understand it the water comes in via the thermostat.
It turns right through the small (currently blocked) holes, through the engine block and back into the exhaust duct.
Im a bit unclear on the exact re entry point as it us all utterly clogged.
View attachment 70326

View attachment 70327



Im off to get some brick cleaner which i hope will sort the coolent unit i have taken off the engine.

The engine block is going to be more of an issue.
Ill wiggle about with some wire.
If i can get some flow through is it appropriate to mix some brick cleaner into the water and run it through the engine?
Id appreciate some advice on what liquid I can use to clear out the engine side pipes.

Thanks all
Click to expand...


The exhaust outlet bend is #1 in the diagram I posted

The water flow is from the pump to a Tee in the coolant pipe under the exhaust manifold. Here it divides.

Some flows to and from the engine cooling passages via the manifold ( this could well be blocked ) and leaves via the thermostat.
The remainder flows to the bypass in thermostat cover, where it is joined by hot water leaving the engine via the thermostat. The whole lot then flows via hose #7 to the water injection point in the outlet bend .



Diagram of the whole cooling system can be found on the parts website at http://www.marinepartseurope.com/en/volvo-penta-explodedview-7742080-26-13636C.aspx
 
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stu9000 said:
Yard advice is to just manually clean the holes. The pipe diameter widens in the engine so hopefully should be OK just cleanibg up the pinch points
Click to expand...

The injection point ibto the exhaust bend is almost ceratinly blocked, or you would get some flow.

The passage(s) in the manifold are also very probably blocked. If you do not unblock these the engine will overheat

You will have to at lesat partially unblock it all manually in order to get any acid cleaner through
 
I had the exact some problem in the end I replaced the manifold for peace of mind never had the problem again.

The engineer suggested the previous owner had run the engine at low reves for too long, i now run it at 2,500 when just under engine.
 
stu9000 said:
Hole in bottom left of Pic.
Isn't that the water injection point?
Click to expand...

The water inlet to the manifold is underneath near the back end. The picture is of the front end.

Make sure the passages from that inlet to both the front and back parts of the cylinder head are clear. The passage to the front part may well be quite solidly blocked!
Make sure all the other passages in the manifold are clear too.

Then turn your attention to the exhaust outlet bend. Make sure the exhaust gas passage it not excessively choked with carbon and make sure the water passage is clear of all restriction. Check the external pipework and hoses too

You could of course save all the hard work by replacing the manifold as derekgillard claims to have done. It only costs £1900. While you are at it replace the outlet bend too for £126. You may have to replace the latter anyway if it is badly corroded
 
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VicS said:
The water inlet to the manifold is underneath near the back end. The picture is of the front end.

Make sure the passages from that inlet to both the front and back parts of the cylinder head are clear. The passage to the front part may well be quite solidly blocked!
Make sure all the other passages in the manifold are clear too.

Then turn your attention to the exhaust outlet bend. Make sure the exhaust gas passage it not excessively choked with carbon and make sure the water passage is clear of all restriction. Check the external pipework and hoses too

You could of course save all the hard work by replacing the manifold as derekgillard claims to have done. It only costs £1900. While you are at it replace the outlet bend too for £126. You may have to replace the latter anyway if it is badly corroded
Click to expand...

CORRECTION
Derekgillard clearly did not replace the Manifold it was the outlet bend which was indeed corroded. From memory it cost about £140 and cured the problem.
Apologises for the confusion
 
Before you go mad replacing bits, you can buy a cleaned up MD7a for around 1500 quid from marine enterprises ltd.
http://marineenterprises.apolloduck.net/detail.phtml?id=340722
I would imagine slapping a fresh engine onto the existing sail drive is a relatively DIY-able job, but I don't know.

You've probably got the same set up as me, MD7a & 110 sail drive given that it's near enough the same boat.
The flow seems to be a bit of a trickle at the best of times.
 
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Hook a small bilge pump, or pond pump up to the coolant system in such a way that the pump is submerged in a bucket of Rydlyme, pumping it through the raw water pump outlet pipe, through the engine and back to the bucket, from the pipe that goes to the exhaust, so it circulates the Rydlyme around and around the engine. Leave it running for 2 or 3 hours. As this won't do the elbow you will need to manually clean it, soak it in the bucket whilst it's pumping, or replace it.
 
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