MD2020 temperature measurements

[AHoy2]

As follow-up to an overheat event on my VP MD2020 I have made some temperature measurements and would like the opinion of forum members with real world data/experience to compare with.

The measurements were made after one hour running at a steady 2,000 rpm, with a corresponding boat speed of just under 5 kts. An extended full load test is to follow once I have verified the data so far. The boat is a 31ft AWB fitted with a KIWI prop that is pitched to give 3,500 rpm at WOT.

Temperature measurements (all deg centigrade):
Seawater inlet pipe: 18
Seawater filter: 21
Heat exchanger top adj. to inlet 65
Heat exchnager top adj. to outlet 45
Heat exchanger bottom inlet side 74
Heat exchanger bottom outlet side 56
Exhaust elbow 21

Cyl head at base of injectors: all 3 around 80 deg.
Calorifier feed: 77
Calorifier return: 75

Observations welcome.

AHoy2 you.

 

[Plevier]

I have a 2020D in a 31ft boat with a Kiwiprop pitched for 3400rpm at WOT so very comparable.
I haven't used a thermometer on it but by hand feel and ouch factor @ ca 2200 rpm - my normal cruise - all your first group of measurements sound very sensible except I'm surprised at 3 deg rise between inlet and filter. Is it going through a water cooled gearbox first? My gearbox is not water cooled but I think some earlier ones were, like I used to have on a 2002.
My hot water is very hot, 75 makes sense for the cal feed.
80 on the cyl head sounds sensible but I haven't tried that.

 

[aluijten]

Given the fact that you have a indirect cooled engine I would expect the temperature for the Calorifier feed to be close to the thermostat regulating temperature so around 85 Deg.
If you were running idle for a few minutes before measuring, then your temperatures sound pretty normal. I would only expect the Calorifier return temp to be higher then the feed temperature, basically working in reverse because of the lower idle temperatures of the engine.
Did you measure the watertemp in the Calorifier?

 

[AHoy2]

.... I'm surprised at 3 deg rise between inlet and filter.....

Thanks for confirming that the temperatures seem comparable to those on your installation, also on picking up on the seawater temperature rise.

I believe temperature rise on the sea water feed was a significant factor in the overheating problem, the (original) installation had the seawater inlet pipe to/from the water filter cable tied tightly to the calorifier feed and return pipes for a distance of around 4 feet! I have since spaced the seawater pipe away from the calorifier feeds and insulated it. This had not been picked up on by any of the three different VP engineers that checked the engine overheat problem out over a period of time. Not a very clever installation practice in the first place but stood out like a sore thumb once I started my own trouble shooting. Unfortunately I do not have seawater temperature readings prior to changing the pipe installation, but from hand testing the current 3 deg is a big improvement!

Gearbox is not watercooled BTW.

AHoy.

 

[AHoy2]

Given the fact that you have a indirect cooled engine I would expect the temperature for the Calorifier feed to be close to the thermostat regulating temperature so around 85 Deg.
If you were running idle for a few minutes before measuring, then your temperatures sound pretty normal. I would only expect the Calorifier return temp to be higher then the feed temperature, basically working in reverse because of the lower idle temperatures of the engine.
Did you measure the watertemp in the Calorifier?

From what you say about the calorifier feed temp it seems that the thermostat is opening a bit lower than 85 deg, the cylinder head temps were also lower at 80 deg or so which would confirm this. The measurements were made whilst underway so engine under load, with the calorifier feed temp higher than return as indicated, but point noted if I do any idle speed measurements. Didn't get around to measuring the calorifier water temp, I was single handed and needed to dismantle the companion way to get the measurements so doing the minimum of checks - conscious of being in the Solent with no lookout .

Looks as if a full load test is the next move once I have reliable crew aboard.

AHoy2.

 

[fontmell]

MD2020 overheat

I had an overheat problem this year, basically at full load after about 75/80 minutes the alarm went off and i found the coolant had dissapperared. BUt just gently running around there was no alarm or noticeable cooling loss. My fear was head gasket faliure. The set up is the same as yours re calorifier etc.

Various conversations pointed to exhaust elbow - the bellow exhibited some pressure under load so I replaced the elbow . Still overheating so i took off heat exchanger which was quite 'cruddy' also the thermostat didnt look good so replaced along with flushing engine with rad flush. All is now fine so i conclude even though motor coolant changed every 2 years the sysem had become 'crudded up.
Hope this helps

 

[AHoy2]

fontmell

My engine overheat problem occured the same as yours, had the same concerns and had the complete cooling system stripped, cleaned and tested including the engine coolant pump. Also had the exhaust elbow checked. All done twice within less than a year by two different engineers. Might give the cooling system/motor a go with the radflush prior to doing the next coolant change though as flow seems marginal at the best of times.

I am hopeing that further temperature measurements may help me understand what it is that causes the coolant temperature to go critical, given that the engine has been running under consistent load for an hour or two up to that point. The last event was in choppy seas and could have been due to reduced seawater pick-up. The standard alarm is not a lot of use as it only goes off at the point that the coolant boils and dumps into the bilge!

 

[Plevier]

Given the fact that you have a indirect cooled engine I would expect the temperature for the Calorifier feed to be close to the thermostat regulating temperature so around 85 Deg.

The spec for the 'stat is to start opening at 75 deg and be fully open at 87 deg.
I think running at less than full throttle in not particularly warm conditions it's not surprising if it doesn't run at max temp.
The 2020 has a big heat exchanger, much bigger than the later D1-20 engine.

 

[Plevier]

Thanks for confirming that the temperatures seem comparable to those on your installation, also on picking up on the seawater temperature rise.

I believe temperature rise on the sea water feed was a significant factor in the overheating problem, the (original) installation had the seawater inlet pipe to/from the water filter cable tied tightly to the calorifier feed and return pipes for a distance of around 4 feet! I have since spaced the seawater pipe away from the calorifier feeds and insulated it. This had not been picked up on by any of the three different VP engineers that checked the engine overheat problem out over a period of time. Not a very clever installation practice in the first place but stood out like a sore thumb once I started my own trouble shooting. Unfortunately I do not have seawater temperature readings prior to changing the pipe installation, but from hand testing the current 3 deg is a big improvement!

Gearbox is not watercooled BTW.

AHoy.

I can't believe 3 deg on that would matter. What happens if you have a warmer day!

 

[aluijten]

The spec for the 'stat is to start opening at 75 deg and be fully open at 87 deg.
I think running at less than full throttle in not particularly warm conditions it's not surprising if it doesn't run at max temp.
The 2020 has a big heat exchanger, much bigger than the later D1-20 engine.

For the temperature at Calorifier feed point it makes no difference even if you have a huge heat exchanger. It's the thermostat that regulates the (maximum) temperature at the feed point. Before taking measurements make sure the engine and the calorifier are completely warmed up.
I'm not sure but I believe the coolant circuit that runs through the calorifier bypasses the thermostat. Hence the reason you need to wait until this is heated up as well.
The temperature gauge at the VP dash of my own engine (MD2040) takes quite some time to reach 85 degrees, it also drops back to 75 or so when the engine is running idle.
It takes the temperature at the point where the coolant enters the heat exchanger.

Cheers,

Arno

 

[AHoy2]

I can't believe 3 deg on that would matter. What happens if you have a warmer day!

The 3 deg rise is due to engine bay ambient, prior to re-arranging the seawater pipe and insulating it I estimated the temp rise from seacock to heat exchanger to be in the order of 15 plus deg due to the transfer from the calorifier pipes.

Agree that a rise in airtemp, say from the 8 deg on day of measurement to a 25 deg summer day should be insignificant in terms of coolant water temp. The sea water on the day at 18 deg was about as warm as it gets hereabouts.

 

[Plevier]

For the temperature at Calorifier feed point it makes no difference even if you have a huge heat exchanger. It's the thermostat that regulates the (maximum) temperature at the feed point.
The temperature gauge at the VP dash of my own engine (MD2040) takes quite some time to reach 85 degrees, it also drops back to 75 or so when the engine is running idle.

I don't think I agree with that.
If you have a large heat exchanger - by which I mean a surplus of capacity - then the 'stat will need to let less hot water through to maintain a balance as the ht ex will cool it more. If the stat was a digital device it wouldn't matter but in fact it operates in an analogue fashion over quite a wide temp range, so if you only need a bit of flow it's going to settle near to 75 deg. At full power needing a lot more flow, the stat needs to open further to allow that flow, but to make it open further it has to be hotter. However if it's sized to be adequate for full power with warm inlet water, at mid power with cold water it will never open fully.
I think your own figures give some support to me.
The D1-20 which in most ways is very similar has a much smaller heat exchanger, suggesting to me that the 2020 has a bigger one than is necessary, and therefore likely to show more temp variation with engine load. Sorry I didn't say it more fully.
As a further point, doesn't the calorifier feed come off before the 'stat, so in some conditions heat loss in that circuit could lower the temperature too.
My whole argument does depend on the fact that the thermostat has a significant operating range. In effect it's a simple proportional controller with limited gain. Oh, and a time lag too.

 

[Plevier]

The 3 deg rise is due to engine bay ambient, prior to re-arranging the seawater pipe and insulating it I estimated the temp rise from seacock to heat exchanger to be in the order of 15 plus deg due to the transfer from the calorifier pipes.

sorry misunderstood you. That's amazing.