Volvo MD2020 overheating at high rpm.

[Ric]

I have had my MD2020 since new and it has now done 1100 hours, so I know it fairly well. Over the last 200 hours or so, it has been running hotter than it used to do when new. It will run all day, perfectly happily at 2500-2800rpm, but if I gun along for half an hour or so at 3000rpm, it will get hotter than it used to do and eventually sound the overheat alarm (or cause the calorifier PRV to open and fill the bilges with fresh water). Moreover, if I fill the coolant up to the level which was previously normal and stable, it will always blow a few cc through the overflow pipe. If I leave the coolant level lower than it used to be, then it remains stable at that level.

I have changed (several times) the coolant and made sure that the heat-exchanger is clean. I have carefully checked that the heat-exchanger rubber tubes are correctly and tightly in place. The exhaust elbow is less than 200 hours old. The engine is in good mechanical order - injecters renewed 200 hours ago, valve clearances good. Raw water circuit is all in good order. Thermostat is still the original, but if this was malfunctioning the overheat alarm would sound when running at 3500-2800rpm.

Can anybody suggest anything that might explain the above symptoms? Could a perforated heat-exchanger be the problem - that might explain the small expulsion of coolant.

 

[sailorman]

I have had my MD2020 since new and it has now done 1100 hours, so I know it fairly well. Over the last 200 hours or so, it has been running hotter than it used to do when new. It will run all day, perfectly happily at 2500-2800rpm, but if I gun along for half an hour or so at 3000rpm, it will get hotter than it used to do and eventually sound the overheat alarm (or cause the calorifier PRV to open and fill the bilges with fresh water). Moreover, if I fill the coolant up to the level which was previously normal and stable, it will always blow a few cc through the overflow pipe. If I leave the coolant level lower than it used to be, then it remains stable at that level.

I have changed (several times) the coolant and made sure that the heat-exchanger is clean. I have carefully checked that the heat-exchanger rubber tubes are correctly and tightly in place. The exhaust elbow is less than 200 hours old. The engine is in good mechanical order - injecters renewed 200 hours ago, valve clearances good. Raw water circuit is all in good order. Thermostat is still the original, but if this was malfunctioning the overheat alarm would sound when running at 3500-2800rpm.

Can anybody suggest anything that might explain the above symptoms? Could a perforated heat-exchanger be the problem - that might explain the small expulsion of coolant.

is the raw water pump working correctly, have you checked the wear plate in the back of the pump, is the front plate worn

 

[<152587>]

Thermostat is still the original, but if this was malfunctioning the overheat alarm would sound when running at 3500-2800rpm.
.
/QUOTE]

Not necessarily, stat could be stuck in partially open position allowing sufficient cooling at that load, or maybe not fully opening.

 

[RichardS]

Probably worth checking the thernostat in a pan of boiling water as thirdengines suggests or just fitting a new one as this could cause engine to runner hotter than normal.

Slight loss of coolant could be the coolant filler cap opening slightly at too low a pressure and causing some vapour loss. Might be worth replacing or see if you can borrow one from someone with the same engine.

Otherwise you seem to have covered all bases so I'm rather bereft of ideas.

Richard

 

[alan]

Could be a fouled propeller. Does the engine overheat when you are not in gear? If you are in gear do the revs increase as you open the throttle up to 2800 revs, but then stick at 3000 even though you continue to open the throttle?
I have had overheating problems (alarm) due to a fouled prop and opening the throttle to a point where the revs no longer increase with throttle, and then after a while the overheat alarm goes off. With a clean hull and clean prop you should be able to achieve around 3600 revs in gear ....... but this max will reduce as the hull and prop become fouled.

Just a thought.
Alan.

 

[VicS]

I have had my MD2020 since new and it has now done 1100 hours, so I know it fairly well. Over the last 200 hours or so, it has been running hotter than it used to do when new. It will run all day, perfectly happily at 2500-2800rpm, but if I gun along for half an hour or so at 3000rpm, it will get hotter than it used to do and eventually sound the overheat alarm (or cause the calorifier PRV to open and fill the bilges with fresh water). Moreover, if I fill the coolant up to the level which was previously normal and stable, it will always blow a few cc through the overflow pipe. If I leave the coolant level lower than it used to be, then it remains stable at that level.

I have changed (several times) the coolant and made sure that the heat-exchanger is clean. I have carefully checked that the heat-exchanger rubber tubes are correctly and tightly in place. The exhaust elbow is less than 200 hours old. The engine is in good mechanical order - injecters renewed 200 hours ago, valve clearances good. Raw water circuit is all in good order. Thermostat is still the original, but if this was malfunctioning the overheat alarm would sound when running at 3500-2800rpm.

Can anybody suggest anything that might explain the above symptoms? Could a perforated heat-exchanger be the problem - that might explain the small expulsion of coolant.

The order in which I would consider things are

1. raw water inlet / strainer

2. Seawater pump. You don't mention checking/ replacing the impeller! As said, the pump could also be worn if its done a lot of hours.

3. Thermostat not opening fully

4. perforated heat exchanger ?? ........ probably not if the coolant level is stable at the slightly lowered level ...

 

[RichardS]

The order in which I would consider things are

1. raw water inlet / strainer

2. Seawater pump. You don't mention checking/ replacing the impeller! As said, the pump could also be worn if its done a lot of hours.

Although the OP does say that the "Raw water circuit is all in good order" so I assumed that both the strainer and inpeller were good to go. No harm in double checking though.

Richard

 

[VicS]

Although the OP does say that the "Raw water circuit is all in good order" so I assumed that both the strainer and inpeller were good to go. No harm in double checking though.

Richard

If the others have been checkd then thermostat no1

but .... not so easy to get at on an MD2020 is it ?

 

[fontmell]

Hi

I would firstly change impellor and reverse end cover when re fitting.
As an aside how do you replace the thermostat
thanks

 

[parbuckle]

Maybe a problem with flow to sea pump not easy to see could try substituting transparent plastic pipe to view any air pockets.

 

[sailorman]

Hi

I would firstly change impellor and reverse end cover when re fitting.
As an aside how do you replace the thermostat
thanks

remove the cam to get the wear plate out & check it for pitting ( its brass) replacements are available from ASAP Supplies

 

[VicS]

Hi


As an aside how do you replace the thermostat
thanks

2020 ( and 2010) you have to remove the heat exchanger, it's in that.

for completeness:
In 2030 engines its in the coolant pump
in 2040 engines its accessible under a cover on the side of the heat excahnger

 

[Ric]

Thanks for the replies. Looks like it can only be the thermostat.

To cover the other suggestions, the raw water circuit is all in very good order - just replaced the pump back plates and seals, and impeller is in good order. Definitely not fouled prop - I swim under the boat regularly.

 

[gandy]

When it overheats, does the raw water from the exhaust get hotter than usual?

 

[VicS]

Thanks for the replies. Looks like it can only be the thermostat.

To cover the other suggestions, the raw water circuit is all in very good order - just replaced the pump back plates and seals, and impeller is in good order. Definitely not fouled prop - I swim under the boat regularly.

Please dont say you have taken the trouble to overhaul the pump body and then stuck an old impeller in it,
Did you replace the cam as well as the end plates ?

 

[Ric]

When it overheats, does the raw water from the exhaust get hotter than usual?

Yes, but not by much. In normal running, the EGT is about 36-38C (as measured by NASA EG-1). If I gun the engine hard, I can push the EGT up to about 46C - then shortly afterwards usually the PRV of the calorifier opens, dumps the contents, and triggers the bilge alarm.

 

[lw395]

Yes, but not by much. In normal running, the EGT is about 36-38C (as measured by NASA EG-1). If I gun the engine hard, I can push the EGT up to about 46C - then shortly afterwards usually the PRV of the calorifier opens, dumps the contents, and triggers the bilge alarm.

So it sounds as if the heat exchanger is not getting the heat into the sea water, rather than a shortage of seawater flow.
So, are some heat exchanger tubes blocked? Is it full of scale etc?
Is the heat getting to the heat exchanger? Lack of coolant flow due to thermostat, not enough coolant in the HE, some obstruction such as bits of delaminating hose or lumps of gasket sealant?

An IR thermometer to see which bits are getting hot might be useful?
Sounds like the heat is going to the calorifier rather than the HE.

 

[billmacfarlane]

I had a similar problem with my Volvo 2030 with 120 SD. It ran full revs in neutral for as long as you liked and below 1500 revs in gear but anything above that caused the beast to overheat. Turned out to be a partially blocked inlet seacock which was of course a b&£)(;r to get to. I decided to get an extra skin fitting installed and a Vetus water filter fitted. Your problem could be there is not enough water getting to he calorifier.

 

[Snowgoose-1]

Is it really necessary vic to speak to someone like a child ? Your manners sir are appalling .

 

[Steve_N]

Your symptoms fit with a loose circulation pump impeller, although I know nothing about a 2020 circulation pump in particular. Often the impeller/turbine is just pressed onto the end of the pump shaft and I've seen a few that have become a loose fit. They tend to keep up at low revs and everything runs fine but then they start to slip at high revs and don't provide enough coolant circulation. Just an idea..