volvo penta MD11C - poor exhaust outflow

[SAWDOC]

hi folks,
I have put a good effort into resolving low exhaust outflow and occasional overheating on my VP MD11c. I find the engine itself solid and reliable but unfortunately despite my efforts to date, I have not managed to solve the occasional overheating problem. The exhaust outflow when measured with a bucket is about 1.25 ltrs per minute. (Can anyone provide a comparison output from their exhaust ?) To my eye that looks insufficient. IF I leave the engine in neutral and increase the revs the exhaust outflow doubles.
I have sought help on this forum on a number of occasions, and I have gone through the step by step approach as follows
Replaced impeller
Replaced raw water pump seals and shaft
Dismantled heat echanger and inspected for blockage (seemed ok)
Dismantled exhaust manifold and inspected opes (seemed ok as far as one could poke a steel wire)
Replaced exhaust elbow
At this stage I have ordered parts for a new skin fitting and will create a new inflow to the raw water pump .
Having tried all of the above over the last few seasons, I have had very little success in increasing exhaust outflow. Any suggestions please?
Thanks as always

 

[Balbas]

hi folks,
I have put a good effort into resolving low exhaust outflow and occasional overheating on my VP MD11c. I find the engine itself solid and reliable but unfortunately despite my efforts to date, I have not managed to solve the occasional overheating problem. The exhaust outflow when measured with a bucket is about 1.25 ltrs per minute. (Can anyone provide a comparison output from their exhaust ?) To my eye that looks insufficient. IF I leave the engine in neutral and increase the revs the exhaust outflow doubles.
I have sought help on this forum on a number of occasions, and I have gone through the step by step approach as follows
Replaced impeller
Replaced raw water pump seals and shaft
Dismantled heat echanger and inspected for blockage (seemed ok)
Dismantled exhaust manifold and inspected opes (seemed ok as far as one could poke a steel wire)
Replaced exhaust elbow
At this stage I have ordered parts for a new skin fitting and will create a new inflow to the raw water pump .
Having tried all of the above over the last few seasons, I have had very little success in increasing exhaust outflow. Any suggestions please?
Thanks as always

There's a danger of fixating on one 'symptom' of a problem and ingnoring other clues IME. I've done it many times.

Looking at your list above, I have 2 suggestions.

1) something that was suggested to me, if any air can get into the raw water pump (usually through a very nearly but not quite flat cover plate apparently), I'm told it can lead to overheating.
2) This one is from my experience. My heat exchanger looked absolutely fine to me but
a) the stack jacket was incorrectly located and was limiting the flow of the engine coolant.
b) what looked to me to be fine was actually leaking like a sieve - the solder holding the tubes to the end plates had broken down and so small amounts of raw water was being allowed to escape into the engine coolant.

I don't know where you are, but these guys did a great job of testing, cleaning and sorting my heat exchanger. http://www.southwestheatexchangers.com

 

[scottie]

Are you sure that you put the heat exchanger end cap and gaskets back on correctly.
The water flow is determined by the cover and gasket being in the correct rotation and should flow along one quarter of the tubes returning through the next quarter going forward again and finally back to the outlet .
If you put the blank cover plate gasket on the wrong way you can stop the flow going through half the tube stack.
Again. If you look at the stack you will see a T section divider.
It is natural that the water flow will increase with the speed of the pump

 

[RichardS]

hi folks,
I have put a good effort into resolving low exhaust outflow and occasional overheating on my VP MD11c. I find the engine itself solid and reliable but unfortunately despite my efforts to date, I have not managed to solve the occasional overheating problem. The exhaust outflow when measured with a bucket is about 1.25 ltrs per minute. (Can anyone provide a comparison output from their exhaust ?) To my eye that looks insufficient. IF I leave the engine in neutral and increase the revs the exhaust outflow doubles.
I have sought help on this forum on a number of occasions, and I have gone through the step by step approach as follows
Replaced impeller
Replaced raw water pump seals and shaft
Dismantled heat echanger and inspected for blockage (seemed ok)
Dismantled exhaust manifold and inspected opes (seemed ok as far as one could poke a steel wire)
Replaced exhaust elbow
At this stage I have ordered parts for a new skin fitting and will create a new inflow to the raw water pump .
Having tried all of the above over the last few seasons, I have had very little success in increasing exhaust outflow. Any suggestions please?
Thanks as always

Probably the simplest thing to do is to feel/measure the temperature of the water coming out of the exhaust. If it's cool or barely warm, say within 10 degrees of the sea temperature, then it cannot be a limited volume of water which is causing the problem but might be incorrect flow as described above. If the temp of the water feels reasonably warm or hot, say more than 10 degrees hotter than sea temperature, then the problem might well caused by too little flow.

The temp ranges above are just my intuition but you might be able to find a better guide on the web.

Richard

 

[mogmog2]

You've done a lot of the obvious, so you're at the scratching around stage so I'll add these other possibilities for low flow:
Worn cover plate - water pressure is lost over the impeller vanes. You can see if it looks badly worn and you can, with some Johnson pumps, flip the cover over (after cleaning it back to shiny). The clearance is pretty close tolerance, as indicated by the very thin paper gasket.
Worn impeller vane deflector - water pressure is lost over the vane tips. On some pumps, this is replaceable.
Air on the intake side has been mentioned - but you're renewing this otherwise also check the strainer and possible poorly-fitted hoses.
Another theoretical one- don't know if this has ever happened- the intake hose collapses under suction, especially with heat in the engine area.

 

[SAWDOC]

Are you sure that you put the heat exchanger end cap and gaskets back on correctly.
The water flow is determined by the cover and gasket being in the correct rotation and should flow along one quarter of the tubes returning through the next quarter going forward again and finally back to the outlet .
If you put the blank cover plate gasket on the wrong way you can stop the flow going through half the tube stack.

I am aware of the need to orient the gasket correctly. However I thought that this was limited to ensuring that the gasket with two opes was lined up properly with the inlet from the raw water pump and the outlet to the heat exchanger. I dont see any particular orientation for the blank gasket other than to ensure it does not leak? Perhaps I am overlooking something.
Also I assumed the inflow flowed towards the blank end bounced off the end and returned to the outlet. Cant really see what would cause it do the quarter flow as you describe. Thank you for your helpful comment.

 

[SAWDOC]

Y
Worn cover plate - water pressure is lost over the impeller vanes. You can see if it looks badly worn and you can, with some Johnson pumps, flip the cover over (after cleaning it back to shiny). The clearance is pretty close tolerance, as indicated by the very thin paper gasket.

Yes worth doing. did it once before.

Worn impeller vane deflector - water pressure is lost over the vane tips. On some pumps, this is replaceable.
Is this the cam internal in the pump housing? On my pump it is replacable . however it is brass so would it wear sufficiently to severely limit flow?

My pal who had a similar engine tells me he used to get about 10 litres per minute exhaust outflow. i am currently getting about 1.25 ltrs /min so my efforts are now focused on improving the exhaust outflow.

Air on the intake side has been mentioned - but you're renewing this otherwise also check the strainer and possible poorly-fitted hoses.

We hope to do the following test on Thursday;
Replace the pump intake with a short section of well fitted new hose fed from a bucket we will keep topped up. See what the drawdown from the bucket is per minute. If the flow rate is significantly above the 1.25 lt/min rate, we have a strong indication of the source of the problem

Another theoretical one- don't know if this has ever happened- the intake hose collapses under suction, especially with heat in the engine area.


No not an issue with braided reinforced hose.

Thank you for taking the trouble to comment :encouragement:

 

[scottie]

I am aware of the need to orient the gasket correctly. However I thought that this was limited to ensuring that the gasket with two opes was lined up properly with the inlet from the raw water pump and the outlet to the heat exchanger. I dont see any particular orientation for the blank gasket other than to ensure it does not leak? Perhaps I am overlooking something.
Also I assumed the inflow flowed towards the blank end bounced off the end and returned to the outlet. Cant really see what would cause it do the quarter flow as you describe. Thank you for your helpful comment.

Perhaps I am not explaining it clearly then but it is essential that the water goes through all the tubes and this is dependent on the gaskets and caps being in the correct alignment
If you take the covers off you will see the divider I have not assembled one for many years so can not recollect exactly but you should be able to work it out

 

[RichardS]

My pal who had a similar engine tells me he used to get about 10 litres per minute exhaust outflow. i am currently getting about 1.25 ltrs /min so my efforts are now focused on improving the exhaust outflow.

Good grief .... that's 1 litre every 6 seconds. At idle my twin 30 bhp Yanmars probably pulse about twice every 6 seconds but each pulse is nothing like 500 ml. Probably more like 100 ml which would make my flow rate something like 2 litres a minute.

10 litres a minute sounds amazing.

Richard

 

[Slowtack]

Data for Volvo D1-30 here... http://www.darthaven.co.uk/userfiles/products/files/Technical data D1-30.pdf
The quoted 1100 litres per hour at 1200 rpm is about 18 litres per minute which might be a bit reduced in practice due to inlet, strainer and other system losses particular to a specific installation. Mine delivers over 10l/min at 900 rpm which seems to agree reasonably well with the quoted rate.

 

[ronmarson]

SAWDOC,
My md11 is at the dockside, keys in the gas locker. try my direct cooled engine for flow, it might give you an indication of expected flow, as my old engine runs well.
I will be on site Wed ev we could try then.
Or give me a ring.
Capt. RoN

 

[SAWDOC]

hi folks
Just an update on the testing.
We disconnected the sea water feed to the raw water pump and substituted a clean unobstructed feed from a bucket. There was a definite lack of suction from the raw water pump. Thumb over the end of the hose could hardly detect suction. So our attention is now focused on the raw water pump itself. Pump housing is clean, impeller and gasket is new so I have ordered a new cam (see mogmog2 post #5 above - thanks mogmog2!). If that doesnt improve matters it seems the more expensive option of new pump housing is required. More anon.

 

[Balbas]

It is natural that the water flow will increase with the speed of the pump

That would seem logical wouldn't it? But it's not true. Assuming he's got a Johnson F4 (which he probably has) raw water pump, the flow rate changes marginally with increased RPM. I've a diagram somewhere of the flownrates of Johnson pumps vs Rpm, I'll try to find it and post it up this weekend.

 

[VicS]

That would seem logical wouldn't it? But it's not true. Assuming he's got a Johnson F4 (which he probably has) raw water pump, the flow rate changes marginally with increased RPM. I've a diagram somewhere of the flownrates of Johnson pumps vs Rpm, I'll try to find it and post it up this weekend.

It is true.
Here are the performance figures from Johnson pumps' catalogue

 

[SAWDOC]

VicS
Thanks .Very interesting.
Does the bar/feet column on the left represent the head against which the pump has to work? and is the data specific for engine cooling pumps rather than say bilge pumps?

 

[scottie]

It is true.
Here are the performance figures from Johnson pumps' catalogue

Top line idle to full power 3to 9 GPM seems like an increase to me?

 

[Balbas]

It is true.
Here are the performance figures from Johnson pumps' catalogue

Top line idle to full power 3to 9 GPM seems like an increase to me?

Ok, I perhaps should have been more precise. The graph isn't as linear as you would expect. I'm still working on the thought that the chap has an F4 pump by the way. The graph I was looking at is in here. https://www.dropbox.com/s/0w6acer1s8qtu87/Johnson Pumps (detailed).pdf?dl=0 And in comparison with other pumps where the output increases markedly against rpm, this is much less so with the F4

Edit page 6 of the linked document. On my tablet I can't extract just the graph.

 

[VicS]

Ok, I perhaps should have been more precise. The graph isn't as linear as you would expect. I'm still working on the thought that the chap has an F4 pump by the way. The graph I was looking at is in here. https://www.dropbox.com/s/0w6acer1s8qtu87/Johnson Pumps (detailed).pdf?dl=0 And in comparison with other pumps where the output increases markedly against rpm, this is much less so with the F4

Edit page 6 of the linked document. On my tablet I can't extract just the graph.

This graph presumably, but the scale is pretty useless to show the performance of the F4 pump

If you plot the data from the table on to a more sensible scale you can see how the performance varies with speed ... very close to being linear

 

[DaveyG]

Maybe in the wrong direction for your engine, but I had a similar issue with my Yanmar at the weekend. poor exhaust water flow and overheating after a while.

After a bit of checking noticed that the seawater filter wasn't purging, and lots of back pressure in the system. I suspected a blocked exhaust elbow, so took the rubber hose off the elbow and attempted to blow down it, it was partially blocked, checked air lock and that was ok, then I checked a wet muffler box and the inlet plastic had melted and blocked the gas and water flow, I gouged out the plastic to create flow and put it back together.
Fixed the issue, good gas and water flow.

The yacht is new to me so dont know why the blockage happened, I'm going to replace all the seawater pipes as they look bloated. Can't remember the name of the muffler box, it was a plastic 5l oil can shape. I'll try to by-pass it to see if I can cope with the noise, else I'll replace it

Like I say, maybe not your issue but maybe worth a bit of a play

 

[SAWDOC]

I am awaiting the delivery of a new cam for the raw water pump hopefully mid week. Has anyone replaced a worn looking cam to good effect? The alternative more expensive option is to replace the pump housing which is a more expensive option and hopefully wont be required.