BUKH DV20 Temperature sender. Faulty?

[b4bu]

I've replaced the manifold, the thermostat housing and the thermostat on my DV20. I reused the old temperature sender. But I can't seem to get it right. The gauge gives silly values, mostly it's at maximum although the engine does not seem hot and the cooling water flows through fine.

The temperature sender has two connectors, one big and one small. The big one is for the gauge and the small one is for the alarm, right? But, alas, the previous owner has replaced the cable shoes with two identical ones, and I didn't take note when I disconnected them..., so now I don't know which cable is for which connector. Is there a way follow the wires to figure it out?

Also, I suspect the sender might have become damaged/faulty. Could I have ruined it somehow by messing with the cables? Is there a way to test this? (The sender is basically just a resistor changing with temperature, right? Should be possible to measure the resistance while putting the sensor in water of different temperatures?)

Any help or hints is appreciated. Please excuse my mediocre english. Hope it makes some sense.

Thanks,

Baard
Norway

 

[mjf107]

I've replaced the manifold, the thermostat housing and the thermostat on my DV20. I reused the old temperature sender. But I can't seem to get it right. The gauge gives silly values, mostly it's at maximum although the engine does not seem hot and the cooling water flows through fine.

The temperature sender has two connectors, one big and one small. The big one is for the gauge and the small one is for the alarm, right? But, alas, the previous owner has replaced the cable shoes with two identical ones, and I didn't take note when I disconnected them..., so now I don't know which cable is for which connector. Is there a way follow the wires to figure it out?

Also, I suspect the sender might have become damaged/faulty. Could I have ruined it somehow by messing with the cables? Is there a way to test this? (The sender is basically just a resistor changing with temperature, right? Should be possible to measure the resistance while putting the sensor in water of different temperatures?)

Any help or hints is appreciated. Please excuse my mediocre english. Hope it makes some sense.

Thanks,

Baard
Norway

Hi Baard welcome to the group

As no has replied to this, I'll share my limited knowledge on the subject. Generally temperature senders are NTC thermistors ie their resistance falls with rising temperature I would think there would also be diodes in this sender as well to isolate the 2 outputs, but I've never tested one so cant help more than this. I did a Google search 'Bukh water temperature gauge' and was directed back to this site, try it some useful info comes up, sorry I don’t no how to post a link directly Hope this is of some help

Michael

 

[VicS]

If you test it with a multimeter on an ohms range I suspect you will find continuity between the gauge terminal and earth but not between the warning light terminal and earth. The latter will be open circuit until it reaches its high temperature point when it will become zero resitance in order to activate the warning light.

The resistance of the gauge sensor will vary with temperature..

I'd not expect there to be any diodes involved.

I think the large terminal may be the connection for the gauge

I think the wire for the warning light is yellow/green and the wire for the gauge brown

 

[mjf107]

The latter will be open circuit until it reaches its high temperature point when it will become zero resitance in order to activate the warning light.

The resistance of the gauge sensor will vary with temperature..

I'd not expect there to be any diodes involved.[/QUOTE]


Vic

Are you saying that the warning light and the gauge have separate Thermistors in the one sensor? I never thought of that possibility!!

Michael

 

[b4bu]

Thank you all for helpful replies!

> ... will be open circuit until it reaches its high temperature point when it will become zero resitance in order to activate the warning light.

Ah. In that case the warning light/buzzer should come on if I earth the cable that usually connects to the small terminal, yes? (I need a way to differentiate the two cables, I've got them mixed up...)

Btw; I strongly suspect the sender to be faulty now. The big terminal (the gauge) shows close to 0ohm and the small terminal around 500ohm - at room temperature. This can't be right, even if mix up which terminal is what.

 

[RobBrown]

I replaced my temperature sender on my Bukh 20 one or two seasons back. I can confirm on the two terminal version, the small terminal is for the temp light/alarm and the large terminal for a read out (not used on mine)

I appreciate you are not in the UK, but the replacment VDO sender details are here:

http://www.furneauxriddall.com/acatalog/VDO_Temp_Sender_Earth_Return_with_W_C.html (803/1/23)

 

[VicS]

Vic

Are you saying that the warning light and the gauge have separate Thermistors in the one sensor? I never thought of that possibility!!

Michael

I was assuming some form of temperature dependent "element" .. thermistor??? for the gauge and a temperature activated switch for the waning light.

The wiring for the warning light is the same as for engines without a gauge. When there is a gauge this double sensor is fitted and the second terminal is connected to the gauge.

The wiring diagram is not easy to follow it must be said !

 

[mjf107]

Bukh wiring diagram

I was assuming some form of temperature dependent "element" .. thermistor??? for the gauge and a temperature activated switch for the waning light.

The wiring for the warning light is the same as for engines without a gauge. When there is a gauge this double sensor is fitted and the second terminal is connected to the gauge.

The wiring diagram is not easy to follow it must be said !

+1 on the wiring diagram Did you see my sketch on the resent Bukh stop solenoid thread it shows most of the connections, I think its easer to follow, though time consuming to produce

 

[VicS]

+1 on the wiring diagram Did you see my sketch on the resent Bukh stop solenoid thread it shows most of the connections, I think its easer to follow, though time consuming to produce

I hadn't seen it. You added it after the last time I visited the thread but it all looks to be how I interpreted the diagram in the manual.

 

[steve48]

Hi
The sensor has two independent variable resistors, the small tab being for the alarm.
To check which wire is which, with the “ignition” on, touch a wire to earth. If a buzzer sounds, it is the alarm wire. If it doesn't, it is the other one. NB On my BUKH, the engine has to be running to get the alarm to sound when touching to earth.
If the gauge is showing any deflection, the removal of its wire will give nil deflection. If touched to earth, you will get full scale deflection. If you are already showing full scale deflection with a warm engine, try with the engine cold when presumably you do get nil deflection to start with.
By the way, there are diodes and things on a little circuit board. This is to allow the buzzer to be “shared” by the offending service (temp, oil and, I think, the charging), but only the offending warning light will glow.
I have been troubled by the sensor for some years (it was OK for my first 8 years with the boat).
The temp sensor cracks (if you clean sensor with fine wet and dry you can see tiny parallel lines running the length of the rod). This allows water in which short circuits the variable resistor. People cleverer than me have actually sealed the cracks with solder when the item is is absolutely dry.
There can be a build up of salts in the sensor housing causing this cracking Take it off and check that the sensor is not touching anything. It might also be old age.
Hope this helps.
Steve