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Old 23-07-2020, 01:53   #16
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Re: Adding Temperature Gauge to MD 2020

I was recently working on a friends MD 2020, the stop solenoid had an intermittant fault. In my tracing I discovered that that model is not grounded, I mean that the engine block is not permanently connected to negative, there are relays that engage when stop start etc selected. This would prevent a standard sensor with engine return from operating, you would need a switch type of sensor.
Maybe someone with more knowledge than I might explain this.
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Old 23-07-2020, 02:01   #17
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Re: Adding Temperature Gauge to MD 2020

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Originally Posted by noblewarrior View Post
I was recently working on a friends MD 2020, the stop solenoid had an intermittant fault. In my tracing I discovered that that model is not grounded, I mean that the engine block is not permanently connected to negative, there are relays that engage when stop start etc selected. This would prevent a standard sensor with engine return from operating, you would need a switch type of sensor.
Maybe someone with more knowledge than I might explain this.
There are two terminal pressure sensors available for this very reason. One terminal goes to the gauge and the other to battery negative. They don't use the housing or engine for the negative side of the circuit
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Old 23-07-2020, 02:17   #18
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Re: Adding Temperature Gauge to MD 2020

The reason i posted is to highlight that point, a sensor like the one in a picture in one of the posts will not work on that engine if the block is isolated, you need the switch type.
I was wondering if anyone knows why that engine model has the engine block isolated, I presume it is for electrolosis, but why that model and not others.
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Old 23-07-2020, 03:13   #19
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Re: Adding Temperature Gauge to MD 2020

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Originally Posted by noblewarrior View Post
The reason i posted is to highlight that point, a sensor like the one in a picture in one of the posts will not work on that engine if the block is isolated, you need the switch type.
I was wondering if anyone knows why that engine model has the engine block isolated, I presume it is for electrolosis, but why that model and not others.
Yes, you make a valid point if the engine block is not grounded.

I'm not sure of your terminology though. Around here (and I assume elsewhere) an oil pressure switch is used activate the low oil pressure light while a oil pressure sender is used to drive the oil pressure gauge. Both switch and sender are individually available in single terminal and dual terminal variants. The two terminal variants are used for ground isolated engines.

This is not to be confused with the two terminal combined sender/switch (used on grounded engines) or the three terminal combined sender/switch (used on grounded isolated engines).

In all cases, the pressure sender is electrically isolated from the pressure switch.
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Old 12-08-2020, 06:21   #20
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Re: Adding Temperature Gauge to MD 2020

From the workshop manual:
MD2010-40A = MD2010-40B
MD2010-40B has:
• Unipolar electrical system
• The fly wheel cover and the transmission (reverse gear or S-drive) are electrically insulated from the engine


MD2010-40B = MD2010-40C
MD2010-40C has:
• Heat exchangers with improved cooling performance and extended expansion volume
• Deeper and narrower oil sump
• Reinforced generator mountings for 2010 and 2020
• Common oil filter for 2010-40


The thread is interesting, - I have lately some unexplainable overheating with my MD2020. I might mount some temperature gauge on top of the existing on/off alarm, but that does not explain the "why".
... still considering what I will do, but info above as it looks like relevant for the thread.
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Old 16-08-2020, 23:27   #21
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Re: Adding Temperature Gauge to MD 2020

As a MB owner, I recommend an exhaust temp alarm in addition to anything else. Depending on your layout, and if the engine is Fresh-water cooled, rather than sea-water cooled, the exhaust alarm may fire up before the coolant itself overheats. One time, when the inlet water was accidentally shut off at start-up (which is a cautionary tale of itself), the exhaust overheat alarm saved a disaster. If fitting any instrument make sure that the sender and the gauge are compatible. USA protocol for measuring and displaying the resistance and hence the oil pressure or temp is different from European.
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Old 17-08-2020, 09:50   #22
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Re: Adding Temperature Gauge to MD 2020

I agree with your thoughts, - although I guess that it will not be that easy to fit an exhaust temp sensor. My worry is this: The standard place for the temp gauge is in the heat exchanger. There is a thread there and I only have to unscrew the plug and fit a sensor. Fine. BUT I believe it comes AFTER the thermostat. In case the thermostat does not open, the heat exhanger does not get any coolant, - and stays cold, - while the motor overheats. I will do something but have not really decided on what/how yet.
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Old 17-08-2020, 12:08   #23
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Re: Adding Temperature Gauge to MD 2020

The exhaust overheat alarm won't spot that, (because it's getting some water via the bypass). But if you look at the temp gauge, in the scenario you describe, and after, say, 4 or 5 minutes running, the needle is resolutely stuck on cold, it should raise concerns. You almost need an "under heat" alarm.!
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Old 18-08-2020, 11:09   #24
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Re: Adding Temperature Gauge to MD 2020

... I still agree with your arguments. My thoughts are also around the normal sensor, - the alarm switch. That one is at the pump and I guess it works on the real temperature, - the temp. of the cooling water (not the seawater). That one is to my opinion fine and sufficient. What do I need a gauge for if the thing I want is an alarm kicking off at a certain temperature? I only need a gauge if it gives me some value, - and the exhaust temp may be interesting, - but not the cooling water, - the switch I have is sufficient for that. An interesting thought though is, - as you actually mention, - to measure on the seawater. ... but too complicated, - overengineering. The exhaust temp though could be an interesting challenge. ... as my sudden overheating (twice now) could be either due to a new propeller last year (... I just found one and hoped it fits the boat) and/or mussels on the propeller. Both could result in that the motor is heavier loaded.
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Old 18-08-2020, 23:46   #25
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Re: Adding Temperature Gauge to MD 2020

As regards fitting an exhaust overheat alarm, it is dead easy.
Some, I believe, do require the sender, (which is a thermistor) to have a hole drilled into the exhaust hose, whuch might be a PITA. Others, like mine, have the sender just held close up tight to the exterior of the hose, immediately "downstream" of the raw water injection point/exhaust bend, with a wormdrive clip. Electically, I found it very simple to fit, you need to take electrical power from any convenient point/accessory that is powered by the engine: I spurred mine from the starter switch, but you could spur off from, say, the rev counter, or, indeed, the water temp gauge which we are in the process of fitting.
They aren't eye-wateringly expensive, mine was about £50/US$70, 7 or 8 years back.
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Old 19-08-2020, 08:44   #26
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Re: Adding Temperature Gauge to MD 2020

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Others, like mine, have the sender just held close up tight to the exterior of the hose, immediately "downstream" of the raw water injection point/exhaust bend, with a wormdrive clip.

This is the same setup I went with, I actually have three surface / contact temp sensors (one ring terminalled to engine block, one ring terminalled to transmission, and one hose clamped to exhaust).


The biggest thing to note with the surface mounts, though, is the temps are all relative. If your engine is supposed to run at 180 degrees, don't set your temp alarm at 180 degrees on a temp sensor that is just ring mounted to block as it might alarm way too late. You just need to find the temperature the gauge normally reads at good cruise and use that as your benchmark, if you go above that you might have a problem.



With all three I took the boat out for a regular run at cruising speed, not too strenuous, and noted the temperatures on the three gauges then set the alarms to go off a few degrees higher. I've had to bump up the alarms a few times on the exhaust, but that's always accompanied by a visual inspection that all is well with the cooling system so I don't mind the reminder to check everything out and then, assuming all is well, setting the temp alarm a little higher.


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Old 19-08-2020, 11:21   #27
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Re: Adding Temperature Gauge to MD 2020

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Originally Posted by noblewarrior View Post
The reason i posted is to highlight that point, a sensor like the one in a picture in one of the posts will not work on that engine if the block is isolated, you need the switch type.
I was wondering if anyone knows why that engine model has the engine block isolated, I presume it is for electrolosis, but why that model and not others.
Your presumption is correct, the engine electrical system on the MD2020 was built as a two pole system for corrosion purposes, particularly as relates to saildrive engines.

In the later years of production of the MD2000 series engines VP began using two pole systems to provide electrical isolation between the vessel electrical system and the saildrive. When the 2000 series engines went out of production about 1993, and the Perkins based 2010 - 2040 engines started, the two pole system was carried over in the first generation (A) of these engines.
With the change to the second generation 2010B- 2040B engines, the 2 pole system was dropped and the electrical isolation was achieved by a system of Mylar washers and spacers located in the flywheel housing and saildrive mounting. This system was maintained thru the end of the 2020 engine series, and continues today in the D1 and D2 series of engines.
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