Q for MAN powered boaters (or anyone else in the know)

[MapisM]

I was recommended to replace the sensors of the alarms for high cooling liquid temp and low oil pressure, just because they are by now 14yo.
Allegedly, just unplugging the temp sensors, put them in a pot and check if the contact closes at the right temp is no guarantee of a constantly reliable behaviour, when these things get old...
And checking pressure sensors is even harder, btw.
Wadduthink, folks?

 

[Portofino]

Are theses seperate to the guage sensors / senders ?
Can,t help much as mine has an actual “sensor errors “ function being a bit younger .
I would put some sea miles on the boat and rack a few engine hrs up first .
Then if something needs doing ( hope not btw ) while the engineers are in , so to speak tackle this then ?
At the mo leave well alone and get using it

 

[MapisM]

Are theses seperate to the guage sensors / senders ?

Yes they are, so I'd be surprised if they didn't follow the same principle on 6L engines.
Btw, afaik the bulbs for temp LEVELS (as opposed to ALARMS) are different between mech and electronic engines.
Possibly also in order to be self-diagnosing, though I wasn't aware that they are - I'm just taking your word for it.

But the alarm bulbs are rather simple open/close contacts, driven by either temp or pressure.
I can't imagine how and why they should be different in your engines, but what do I know?
Anyhow, allegedly THESE are the ones which can get temperamental as they get old...

 

[kashurst]

assuming (first mistake) you have actual oil pressure and temp gauges already showing whats happening I wouldn't be rushing to change them. I would, if the opportunity arose as part of service etc, test them if possible.
The low oil pressure switch you can test with the engine running and with it stopped (zero pressure) so you should be able to measure the behaviour of that in situ.

 

[BartW]

after my engine rebuilds, I was quite keen on reading accurate value’s of engine temps and oil pressure,
(we struggled with the readings, there was a combination of a few issues.)
by swapping the sensors P, SB and upper and lower helm, we discovered that quite a few gave different readings, so decided to replace all,

cooling water level sensors were replaced before (they give alarm when they fail)

we didn’t check the temp and pressure alarm sensors, but I know they work,

In case you want to change the alarm sensors, (or any other sensors) let me know,
I can order them in Fiumicino from Ceresoli.
They are not expensive, at least not worth the hassle to check them…

In case you need gauges,
I have ordered from the VDO webshop new 24VDC gauges,
and bulbs for all the old Canados (VDO) gauges

 

[MapisM]

Many thanks B, all VERY interesting indeed.
I might well take you up on your offer in the near future, if so I'll drop you an email.

Time being, can you possibly elaborate on the following:

we struggled with the readings, there was a combination of a few issues.

In fact, I am also experiencing a somewhat unreliable reading, with differences between p/h and f/b instruments, for both cooling liquid and oil temperature.

Btw, I can't remember if you've got the latter - in fact, I've seen several MAN powered boats with just the pressure gauge for oil.
What I half recall is that you've got the small e/r instruments panel, which was a MAN option, or am I dreaming of it?
If so, you should have the two cooling liquid bulbs configured as follows:
a "normal" one dedicated to the e/r panel.
a "dual" one (with a small D stamped near the bulb code), which should drive both the p/h and the f/b VDO gauges.
In my DP, which doesn't have the e/r panel, I only have the second "dual" bulb.

Anyway, as I understand, either bulbs are of RTD type (Resistance Temperature Detector), so the gauges are actually moving depending on the resistance transmitted by the bulb. And one possible problem is that, depending on how the cables are routed, possibly together with others, such resistance value can be affected - potentially introducing differences between the two helm stations.

By chance, does this sound familiar with the problems you experienced?
Actually, I am not too worried about all this because every time I had weird readings, a quick check in the e/r with the thermal gun revealed that the actual temps were very stable, but it's a bit annoying anyway...

 

[BartW]

Before the 2nd engine rebuild we have had a catastrophic engine overheat,
and
before and after the 2nd rebuild, we had fluctuating temp readings,
and
after the 2nd rebuild, we have had a slight overheat because we had a small leak in a cooling water hose

all this made me paranoia about the temp readings for a while,
but gradually we found out the issues:
- A intermittent false contact / change of resistance in a multi connector (under the meter panel in p/h)
- Some connections on the sensors not well enough fixed,
- Old warn sensors.
- A loose connection on a alarm buzzer.

We also had intermittent alarms from the cooling water level sensors, issues at different moments were:

- After changing cooling water, it takes a while before all air is out the cooling system (even after priming at the right place)
- False contact on the sensor connector
- One broken sensor, (the new one MUST be the correct MAN type number, different models available )

In the ph I have indeed oil temp gauges and a few other small gauges, But never bothered about these (yet)


The original ER water temp gauges, were mechanic, with a sensor on a tube,
these are out of order, didn’t find replacements yet (Always use IR gun in ER)

also engine oil pressure gauge and gearbox oil pressure gauge in ER
are mechanically connected (with a pressure hose)

FYI
browsing in my MAN manuals, I found the resistance curves from the oil pressure and water temp sensors