Overheating Volvo Penta MD2040

[landonshaw]

My engine (MD 2040 Volvo Penta) overheated yesterday so I changed the impeller. Did have two fins missing, new from 11 months ago. Restarted the engine and after a little time it overheated again. I am now going to change the thermostat and clean the heat exchanger.
Manuals state to drain the coolant but do not say where the drain plug is. Anyone out there with a MD2040 able to help? I have three different manuals and they all just state this fact, show everything else in fine detail. Thanks
Also, any other ideas that I should try while the coolant is out to help fix the problem?

[atoll]

before you take apart the fresh water side of things,make sure that the problem is not an airlock in the seawater side of things.

if possable check flow of seawater where it injects into the exhaust or at the anti siphon.
exhaust back preassure can cause this problem if the pipes or heat exchanger has been drained.

[landonshaw]

Thanks, yes water is not coming out with the exhaust. I will be taking apart the vacuum valve and cleaning today then testing the system. I will also observe the seawater filter to see if water is being pulled up to it, although if the vacuum valve is plugged, the filter is prevalve and there might not be any water coming in there also.

[atoll]

no water from exhaust!
that is what is causing the over heating,it is not any thing to do with the thermostat or fresh water side of things.

i have in the past had to disconnect the feed to the exhaust mixer and suck on it with the engine running to purge an air lock,till raw water flows.

most common culprit is the anti siphon u bend,the impellor pump cannot overcome the back pressure from the exhaust gasses or the lift.

[landonshaw]

Yes, that is why I changed the impeller first. Today will try the vacuum valve. When you sucked on the exhaust, what did you use? Was the engine running?

[atoll]

Originally Posted by landonshaw

Yes, that is why I changed the impeller first. Today will try the vacuum valve. When you sucked on the exhaust, what did you use? Was the engine running?

i just took the hose off,then started the engine andl sucked till water flowed.

i had a look at the manual for the md 2040,and and this is a bit more difficult as the rubber housing from the heat exchanger,joins directly to the exhaust mixer.

i reccomend taking off the bottom jubilee clip on the back end of the heat exchanger and prise the the rubber away from the nipple on the exhaust mixer so air can pass,jam a screwdriver in there.
then start the engine,stop when a good stream of water flows water flows

reconnect and check exhaust water is exiting the boat,as now the system should be primed.

[colemj]

The raw water system on those engines is marginal, so a broken vane will definitely cause overheating. Like Atoll says, check for blockage in the intake and the exhaust elbow. A partially coked up elbow will cause it to run hot. Did you recover the missing vanes? If not, they are in the intake side of the heat exchanger and will block the flow there. I'm betting that is your problem.

The fresh water side of it rarely has problems, but if you do need to drain the coolant, there is a petcock located on the bottom of the injector side of the engine about halfway back.

Mark

[atoll]

i had another look at the diagram,for you it might be easyer,at the front end of the heat exchanger to disconnect the hose from the impellor pump and anti siphon .,suck on that till water flows,then stop eng and re connect.

[landonshaw]

Thanks, did not find the fins. So will follow both of your suggestions.

[atoll]

will be online for abit longer so if you have any other queries just ask.

tip have a bucket handy when you disconnect the hose from the heat exchanger,and protect the alternator with a cloth which is directly below.

[landonshaw]

I am not on the boat, but going in a little while. That petcock must be just before and below the oil filter then. I believe the oil filter is towards the rear of the engine.

[landonshaw]

so I am thinking to take the vacuum valve of, clean it. Take the hose to the intake side of the heat exchanger off and clean it out. Take out the heat exchanger and clean. Clean anything in the large hose going to the heat exchanger. Put everything back together and start the engine. Check for water at the seawater filter and then at the exhaust coming out of the boat.

[atoll]

Originally Posted by landonshaw

I am not on the boat, but going in a little while. That petcock must be just before and below the oil filter then. I believe the oil filter is towards the rear of the engine.

the antifreeze/fresh water drain is below and back from the injector pump,but it is not nessacary to drain the engine unless you are going to dismantle the heat exchanger.

you dont need to drain unless you want to inspect the front of the heat exchanger tube.

[landonshaw]

I figure since I am at it, might as well make a day of it so will take out the heat exchanger and clean. Take it off of my lsit of things to do.

[atoll]

they reccomend,after draining to flush the engine.
and when refilling to use a 50% antifreeze mix.
a welding rod is usefull for cleaning out the tubes,as is vinegar.
be very carefull not to damage the boots either end of the heat exchanger,also you may have to use some silicone if the resevoir is corroded when putting it back together for it to seal properly.