Bukh alarms - again

[EASLOOP]

I have a DV10 with an alarm problem. It works as earlier noted by Vic Mallows but with the following twist.
After the engine has been started the lights go out except the water temperature light. The alarm then sounds continuously. Now the engine is not over heating as this happens immediately the cold engine is started.- no time to heat up yet. Not sure how the temp sender works - does it go to ground through the sensor when over heating? or is it normally held to ground and releases when the temp sender operates? or is it something to do with the alternator?
Suggestions welcome
all the best
John

 

[Stemar]

Most temperature alarms are fed +12v, and earthed -12v through the temperature sender on the engine. If there's only one wire on the sender, that's how yours works.

Disconnect the wire from the sender. (If the engine's running beware of alternator and drive belt(s)). If the warning light goes out and the alarm shuts up, it 's the sender switch that's faulty. If not, you'll have to follow the wire up to the control panel and dsconnect there. Blissful silence means the wire is faulty. If the light/alarm is still on, you'll have to look inside the control panel. Some of them have electronics which mean you may need professional help. The most likely thing is either a faulty engine sensor or a wiring fault.

 

[arTThur]

Hi EAsloop,

I have had a similar problem with my DV20 for the past season - I think that I have finally traced it down and cured it. My over temp alarm came on at starting and would not go out, just like yours. I traced the wiring back to the control board and everything looked OK, but even when changing the sensor, the alram would still come on intermittently when the engine clearly was 'cold'.
The eventual problem was that the sensor was faulty and the spare that I carried was also intermittently faulty - a coicidence, but easily explained.
The sensors are hard to find except from Bukh and should be supplied with two male contacts, one larger than the other. The large contact is normally open and closes when it hits the alarm temparature; this in turn closes the circuit and sets off the alarm sounder. You can check this by disconnecting the wire and the alarm sounder should be silent - if not your wiring really is at fault. The other contact is a graded contact which varies as the temperature rises and falls and is used to input to an electrical temparature gauge - don't use this one for the sounder circuit.
I verified my problem by removing the wire (purple I seem to remember) whilst the engine was running and the sounder was silent. Reconnect and the sounder was activated even though the engine had only just started. Put the suspect sensor in a pan of water and heated it up and a tiny stream of bubbles came out of the body - it had corroded with age and was letting water in through a tiny hole in the body. By a strange coicidence (or maybe not), the spare also had the same problem.
£50 later and a new sensor from Bukh gave no bubbles in water up to boiling point - maybe my spare was relegated to spare status as a result of this intermittency.
Have run engine for over 30 hours since some under full power and not even a hint of the sounder.
Try the water test and see if yours has bubbles, I bet it has.

Good Luck.

 

[VicMallows]

There was in fact a faulty batch of the BUKH sensors a good few years back which showed just this problem. I succeeded in extracting a free replacement from BUKH which has given no trouble since, but if unable to achieve this would have made an adapter for a suitable car one ... or made an electronic alarm ... rather than £50! T

I seem to remember that the *small* terminal is the contact terminal? ...but could well be wrong ....will have to have a look!

BTW, should you ever need an oil-pressure switch, I found a standard car one to suit easily. (Just got the Halfords chap to look through several till we found one).

Vic