Overheat alarm Volvo MD2020 - D

[Crowblack]

The overheat alarm came on yesterday and again when l ran the engine this morning. Engines done about 350 hours.

Both times came on after running about 15 min from cold.

The sea water side seems fine, checked the impeller before launch and the usual amount of water comes out of the exhaust.

So it seems the problem is on the freshwater side, checked the coolant level before each start and it was fine.

Taken the fan belt off to check rotation of freshwater pump and it's smooth with no stiffness anywhere in its rotation, no play in the spindle either - so l'm assuming (?) It's OK.

My questions are because it's (well looks like) on the freshwater side can l assume the tube stack in the heat exchanger is fine ?

Second (and my favourite deduction so far) is it likely to be the thermostat which (happy days) on the MD2020 is a pig to get at.

If it is any tips for the dismantling process.

David.

 

[VicS]

The overheat alarm came on yesterday and again when l ran the engine this morning. Engines done about 350 hours.

Both times came on after running about 15 min from cold.

The sea water side seems fine, checked the impeller before launch and the usual amount of water comes out of the exhaust.

So it seems the problem is on the freshwater side, checked the coolant level before each start and it was fine.

Taken the fan belt off to check rotation of freshwater pump and it's smooth with no stiffness anywhere in its rotation, no play in the spindle either - so l'm assuming (?) It's OK.

My questions are because it's (well looks like) on the freshwater side can l assume the tube stack in the heat exchanger is fine ?

Second (and my favourite deduction so far) is it likely to be the thermostat which (happy days) on the MD2020 is a pig to get at.

If it is any tips for the dismantling process.

David.

The HE has to be removed

Instructions in the w/s manual at https://www.manualslib.com/manual/500402/Volvo-Md2010.html?page=63#manual

Before going to all that trouble I would concentrate on measuring the temperature if you do not have a temp gauge which confirms the assumed high temp. It may be just a faulty alarm sensor. That might be easier to remove and check than the thermostat

 

[Crowblack]

The HE has to be removed

Instructions in the w/s manual at https://www.manualslib.com/manual/500402/Volvo-Md2010.html?page=63#manual

Before going to all that trouble I would concentrate on measuring the temperature if you do not have a temp gauge which confirms the assumed high temp. It may be just a faulty alarm sensor. That might be easier to remove and check than the thermostat

Thanks Vic.

Local Volvo engineer suggested same thing apparently they use a laser thermometer to check running temperature l'm off to buy one tomorrow.

Also got a thermostat and gasket coming just in case.

 

[Ruffles]

I think you'll end up taking out the thermostat even if it's just for peace of mind. Ours failed many years ago in Poole.

Don't just replace it. Pop the new AND the old in saucepan and watch as the temperature rises. Ours wasn't opening fully. If it IS faulty then you'll now KNOW you've fixed it. Peace of mind is half the battle.

Don't forget you'll need a new water pump gasket. I think.

I find the heat exchanger box on ours gets just too hot to hold a hand against in normal use. I imagine it would be cooler than usual if the thermostat is the issue?

But an IR thermometer is really useful and takes out the guesswork. You can even check the stern gland. Great for cooking too.

 

[VicS]

The thermostat should just begin to open at 75 ±2 C and be fully open at 87 C

Its not always easy to see the point at which they just begin to open unless suspended by a thread trapped in it then it drops off the thread as soon as it starts to open

I think you'll end up taking out the thermostat even if it's just for peace of mind.
Don't forget you'll need a new water pump gasket. I think.

.

A New heat excahnger to cylinder head gasket, but not a water pump gasket for an MD2020 !
#19 in this diagram http://www.marinepartseurope.com/en/volvo-penta-explodedview-7740690-25-4152.aspx

 

[JohnGC]

I've just replaced the heat exchanger housing on my MD2020D. Together with the thermostat.

I also have a IR thermometer which I used to monitor the engine during a 3:30 motor at 2500rpm.

The top of the heat exchanger housing never rose above 60C, the hottest part of the engine I could find was 90C.

I'd be very interested to know what figures you measure if you do buy an IR thermometer.

(The laser is just a targeting aid BTW.)

John

 

[Crowblack]

Thanks to all for comments.

Update - - used non-contact thermometer and have run the engine up three times for hour and a half.

Strangely no alarm sounded and highest temp reached was 79c - the engine runs sweet as a nut - just like it always has.

Once the highest temp reached it fell back to temps between 69 to 75 there's a 2c plus minus error rate on the thermometer and the difference could also be me not getting the distance perfect every time.

Pretty sure now the overheat was not due to the thermostat as the problem l now have is no hot water to the calorifier.

The pipes get hot for the first few inches but cold thereafter towards the calorifier.

So is it likely an air lock developed in the engine - leading to the two overheat alarms but has now moved on to the calorifier.

I'll drain the freshwater side tomorrow - flush out with fresh water then refill with new 50/50 coolant.

Do l bleed the calorifier with the pump running (cold engine obviously) or will it bleed OK with engine not turning the pump

David

 

[Crowblack]

All done, running well system bled, oil changed (just in case) and calorifier producing hot water.

Thanks again for suggestions.

David.