Temp Alarm - again

[PhilB]

Having replaced the sender in the engine block the alarm is still sounding even when the engine is cold. Does anyone have a diagram of the electronic unit that sits in pedestal with display lights or any experience of replacing / servicing / problems with this unit ?
I have the 'simple' control panel with no gauges or key -- Bav 36 2004.
Audible alarm cancels if I press TEST but lamp still flashes.
If I remove the wire (single) to the sender unit the alarm extinguishes.

[Salty]

A couple of years back "Coastal Rides" in Dover had one of their frequent sales of Volvo odds and ends, including a new "Electronic unit that sits in the pedestal with display lights." Can't remember exactly what it was called, or how much they wanted for it, but somewhere around the £100 mark. So thanks very much and it sorted the problems a treat. Since then Coastal Rides stay on as one of my favourite sites. Apart from that the only major difference between your boat and mine is that mine is two years older and had been badly beaten up by charterers, though it gets lots of TLC now. Replacing that unit was a very straightforward matter of taking off one wire or group of wires at a time and connecting them directly to the same connection on the new unit, though it's still nearly impossible to see in bright daylight. What I'd really like to do though would be to upgrade the engine electrics/electronics so that all of the parameters shown on that panel at the foot of the pedestal can be transferred to my new Raymarine chart plotter where it would be much easier to see.

[Yngmar]

The electronic unit that sits in the pedestal with display lights is called instrument panel, and there's a schematic on page 84+ of the workshop manual (see previous thread). Although something funny seems to have happened with it upon scanning, looks a bit chopped up. Maybe you can find a better copy.

Did you have the boat from new or is it possible that someone already bodged around in the wiring? That's what had happened on another boat with mysterious engine instrument behaviour (the service alternator lamp was permanently lit, even when the ignition was turned off). Upon opening the binnacle, I found someone had hotwired a cable straight from the battery main switch into the binnacle, bypassing the ignition switch, because due to a previous error in wiring on the cockpit panel side the wrong wire was connected to the binnacle and they couldn't figure that out. Probably the work of a "marine professional" ;-)

[PhilB]

Thanks for replies. The boat was not new but has been perfect for past few years and wiring looks untouched. It is beginning to look like I need a new unit. What is confusing is that the simple panel I have ( no gauges) should have a sender unit that is open circuit until overheated. The old and new sender (in the block not the heat exchanger) both vary their resistance with heat and are never opern cicuit.
The diagram doesnt show the internal electronics of the unit so difficult to diagnose further...

[Salty]

From your description PhilB, I'd say that the sender you have that remains open circuit until the engine gets too hot is intended specifically to trigger your high temperature alarm, i.e., there's not a problem until the engine gets too hot. Whereas the other senders you say do not remain open circuit, but vary their resistance with temperature are intended to drive a meter that shows engine temperature throughout its range. Quite why you have both types of sender, I do not know except that they should not be confused one for the other as that would result in misleading information being displayed or heard. As you and I both have the same panels (no gauges) then the high temperature sender you need to use is the one that remains open circuit until the engine is hotter than it should be, and at which point a circuit is made and, if your panel is anything like mine, you get a very feeble alarm which can barely be heard.

[Nigel]

I also have the simple alarm panel, but my oil pressure sender has both resistance and switch outputs. I imagine other senders are likewise.

[CRYSTAL]

Having replaced the sender in the engine block the alarm is still sounding even when the engine is cold.

H Phil

I have the newer version D1-30 and I get the alarm when the sender / wire is disconnected. I do this disconnection on purpose just to ensure the alarms ate working.

So could it be possible that there is a loose connection or break in the wire?  Do a simple continuity check just to make sure.

Apologies if you've done this test before.
Good luck.