Request for help: problems with overheating old Volvo Penta engine

[bacchant]

Hi fellow cruisers, I am currently off the coast of Sweden heading south to escape the cold, but has encountered a problem I was hoping someone here could help me with. I have limited technical experience and have purchased an old Bacchant IV ocean crosser that is somewhat more of "a repair project" than expected..Please excuse my ignorance, I have no formal training and don't know what I am doing....I learn everything by trying and failing and trying again while consulting some books and youtube combined with asking stupid questions..

The engine is a Volvo Penta MD 11c (almost 40 years) is overheating. Yes, it is due for replacement, but I really want to make it last a little longer if possible.. This particular engine model was originally salt water cooled (direct cooling), but was delivered with a heat exchanger and pump as add-on from day one. It is therefore fresh water (indirect) cooled despite the manual saying something else.. I have taken apart the raw water cooling system, serviced it and put it together again. This part now works well from seawater inlet, filter, sea water pump with impeller, heat exchanger, exhaust bend and all the way until exhaust outlet.


However, while the heat exchanger remains relatively cool the engine block becomes way too hot. I therefore assume the enclosed loop of cooling liquid in the heat exchanger is not circulated through the engine block as it is supposed to. As far as I understand it is either something wrong with the mechanical thermostat regulating flow into the engine block (opening up and letting coolant through when temperature exceeds 60-something degrees Celsius) or the external pump installed to push the coolant through the heat exchanger and the engine block. I have taken out and tested the thermostat in a cup of hot water and it works well, so now I am left with the pump...


Then comes my potential idiot-question: how to test a pump like this? I took a similar-looking pump that I removed from under a sink and tested it with a multimeter to confirm resistance. That seems ok. Then I connected it to a battery and confirmed that it rotates/spins. Again, ok. But when I connected hoses to it and tried to move water from one bucket to another no water goes through.. why? Another thing that confuses me is that of the two electric cables from the pump installed and connected to the heat exchanger one goes to the alternator while the other is only connected to a bolt on the engine itself.. That seems like grounding, but will that allow electricity to pass through and drive the pump?? When the engine is running there is no way to hear or see whether the pump is actually working / pushing coolant around.


Hope someone out there more knowledgable and experienced than I can help with some advice, I would be extremely thankful for any support on this one!


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[Sailmonkey]

You likely were not able to test it with hoses in two buckets because it’s a centrifugal pump. These pumps are not self priming and need to be filled with fluid to start pumping.


If you take the wire that’s attached to the alternator and attach it to the battery, does the pump run?

If yes, leave it attached to the battery and then run your engine. Does it stay cool?

If yes you’ve got a problem sending power to the pump.

[team karst]

The power lead to the alternator D+ terminal results in the pump running when the alternator is charging. So: is the alternator charging??

Also, it helps to do a quick test on the raw water flow. Does your system have an injection point at an exhaust fitting? If so, that area should be cool enough to keep your hand touching it. Maybe 40 deg C maximum.

Yes, I spent much time fixing my volvo md2030 machine for cooling. It ended up with a simple restriction in the seawater pickup.

[tkeithlu]

I'm trying to order likely causes.

With the engine running and the pump installed, check to see that you have 12v at the pump. If not, trace back to the alternator and check connections for corrosion on both sides of the circuit. That does it for electrical problems, because you already know that the pump spins under power, and it's just about impossible to muck up a centrifugal pump.

That brings you to coolant circulation. My best bet in all this is that the coolant needs flushing and any blockages in the flow removed. If you remove the hose from the suction side of the pump, blocking the pump side hose/fitting, does the coolant freely flow out of the hose? Or, is there a block somewhere in the circuit? If that looks promising, remove the hoses from the pump, and (this is messy) shoot a garden hose with towels packed around it into the discharge hose. Water should come gushing out the other end of the circuit, along with a dead mouse or two. Clear that circuit, refill with coolant that can handle winter in Sweden, and go sailing.

[tkeithlu]

Oh. take it from a hearing impaired skipper: With the engine running and the pump installed, check that the pump is spinning by putting your hand around it, not by listening for it. If necessary, spin the pump without the engine so you know what a spinning pump feels like.

[Allied39]

The pump says 24 volt.
Are you getting 24 volts to the pump? 12 wont do it.
I would ensure pump operation, I like your idea of bucket to bucket to check , however as pointed out, priming may be an issue, but that should not be hard to get past.
Process of elimination, you are doing well by the sound of it.

[Bill O]

Let's start w/the simple potential problems.

Is the bottom of the boat and prop clean of fouling?
Sea strainer clogged?
Pressure cap failing/not holding pressure?

[bacchant]

Originally Posted by Sailmonkey

You likely were not able to test it with hoses in two buckets because it’s a centrifugal pump. These pumps are not self priming and need to be filled with fluid to start pumping.


If you take the wire that’s attached to the alternator and attach it to the battery, does the pump run?

If yes, leave it attached to the battery and then run your engine. Does it stay cool?

If yes you’ve got a problem sending power to the pump.

Thanks for your input and clarification, Sailmonkey! I will try this and report on the result. Many thanks!

[bacchant]

Originally Posted by team karst

The power lead to the alternator D+ terminal results in the pump running when the alternator is charging. So: is the alternator charging??

Also, it helps to do a quick test on the raw water flow. Does your system have an injection point at an exhaust fitting? If so, that area should be cool enough to keep your hand touching it. Maybe 40 deg C maximum.

Yes, I spent much time fixing my volvo md2030 machine for cooling. It ended up with a simple restriction in the seawater pickup.

Thanks for feedback! Yes, the alternator is charging, but I believe its not charging at its expected capacity. I will identify and study the alternator manual to verify.


The injection point leading raw water to the exhaust bend is relatively cool and one of the reasons I believe the issue is with the circulation of cooling liquid in the heat exchanger and engine block.


Again, many thanks!

[bacchant]

Originally Posted by tkeithlu

I'm trying to order likely causes.

With the engine running and the pump installed, check to see that you have 12v at the pump. If not, trace back to the alternator and check connections for corrosion on both sides of the circuit. That does it for electrical problems, because you already know that the pump spins under power, and it's just about impossible to muck up a centrifugal pump.

That brings you to coolant circulation. My best bet in all this is that the coolant needs flushing and any blockages in the flow removed. If you remove the hose from the suction side of the pump, blocking the pump side hose/fitting, does the coolant freely flow out of the hose? Or, is there a block somewhere in the circuit? If that looks promising, remove the hoses from the pump, and (this is messy) shoot a garden hose with towels packed around it into the discharge hose. Water should come gushing out the other end of the circuit, along with a dead mouse or two. Clear that circuit, refill with coolant that can handle winter in Sweden, and go sailing.

Many thanks, keithlu! I will try this as well, greatly appreciated!

[bacchant]

Originally Posted by Allied39

The pump says 24 volt.
Are you getting 24 volts to the pump? 12 wont do it.
I would ensure pump operation, I like your idea of bucket to bucket to check , however as pointed out, priming may be an issue, but that should not be hard to get past.
Process of elimination, you are doing well by the sound of it.

My mistake, Allied39. The one pump that says 24 volt is a spare one I was trying to test, not the one connected to heat exchanger. Thanks for your input.


I am so impressed by this forum!

[bacchant]

Originally Posted by Bill O

Let's start w/the simple potential problems.

Is the bottom of the boat and prop clean of fouling?
Sea strainer clogged?
Pressure cap failing/not holding pressure?

Many thanks for input, Bill O!



The bottom of the boat is nice and clean, I just fixed it this summer and I am also in relatively cold waters with limited fouling. The raw water is working properly, but sea strainer is definitely a source for potential/certain future problems (no filter inside).


What is a pressure cap? Where is it located and what function does it have..?


That might be another source of failure: I don't really understand the function of the pressure tank (connected to the top of silver colored heat exchanger with see-through tube) and what problems it might cause if not working properly..

[bacchant]

I think I answered my own question there...the pressure cap is on top of the heat exchanger I guess..

[MicHughV]

I well familiar with this problem, having owned salt water cooled Volvo's before.

The fix is to remove the cylinder heads.
When you do so, you'll expose the water cooling openings and passages around the cylinders.
You will likely also note, that salt water and other crud have all but blocked these openings.
You will have to clean these openings and passages out.
I used a a file, screwdriver, knife blade, whatever I could find that would fit inside those small openings and passages.
The pieces of crud will eventually be flushed out.

I re-used the cylinder head gaskets, and never had any problem, with engine overheating problems after that.

You should also check the raw water impeller for wear, not only the rubber impeller, but also the outside plate, as this must sit flush with the impeller to work properly. It's not uncommon to have small particles of grit get in here and wear a groove into that plate.This will allow air between the plate and impeller, causing inadequate water flow.

The pressure tank is not the problem, this is a container that controls the coolant water in the heat exchanger.

It's a good idea to add some "anti-freeze" to this container to prevent cooling water freeze up.

[bensolomon]

I would replace the thermostat even though it opened in the water bucket. The opening and closing happens 15 times per minute, and a slight gumming of the thermostat will make a big difference in how it works.