Volvo MD7B warning lights

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Moslund
Posts: 5
Joined: Sun Apr 23, 2017 11:41 am

Volvo MD7B warning lights

Post by Moslund » Sat Jul 22, 2017 7:18 pm

Hi,

I just bought Ballad nr. 2005 (build i Denmark) and I´m pretty happy with it but it does have some smaller (or bigger) problems that i need to take of.
Some of them are engine/electrical matters and i wan´t to sort these out first.

My problem was at first glance a low oil pressure warning light that illuminates when the engine is at operating temperature and idling. Just a little more revs and it is out. I was a little bit concerned about this when I bought it but not as much as I am with my newly discovered problem.
When the ignition is on the warning light for charging and low oil pressure are also on, but the high temperature light is not. I thought this was okay since that temp lamp doesn´t turn on with the ignition on some engines as far as I know. But now I have discovered that the lamp actually does turn on after some time (maybe when then engine is at operating temp) but so vaguely that I didn´t notice it at first.
I hoped that it was a bad connection around the bulb. I tried to but the wire from the oil pressure sender on instead and then the light was as strong as the other bulbs. Now I´m confused. Should the light be on with the ignition? And is it normal that the temp light is vaguely on at operating temp?
I think the sender is on those that lowers the resistance when temperature rises and a guess that will make the bulp light more and more as the temperature rises but still that sounds wird I think. You know - how many lumens indicates an overheating engine :lol:
Maybe it is a malfunctioning temperature sender? But if this is the case it should still be on while the ignition is on, right? The sender is with one wire only so it just grounds the bulb when temperature is to high - so there must be another ground in "ignition mode" and in this case it can´t be the sender that causes this I think... Maybe I´m wrong.
It should also be mentioned that my buzzer doesn't work either. This is my next problem since I don´t expect this to affect my warning light issue...
My gauge panel consists of the three mentioned warning lights, buzzer, ignition key and then an hour counter.

I don´t know if this or even my questions make sense to you but electrical stuff isn´t where I´m strongest so any help is welcomed.
GRP question coming up when this is solved :lol:

Kind regards
Troels

peterohman
Posts: 24
Joined: Sun Sep 30, 2012 8:24 pm

Re: Volvo MD7B warning lights

Post by peterohman » Sun Jul 23, 2017 8:32 am

I have an MD7A. My temp lamp is not illuminated before start of engine. I think it is a simple bi-metal detector that switches on when temp gets to high. But then all lamps are connected through an electronic box that switches on the buzzer when any of the lamps indicate a problem. It can be that box that leeks some power to the temp lamp.
If you have used the engine without any problems I would not worry...
/Peter

Moslund
Posts: 5
Joined: Sun Apr 23, 2017 11:41 am

Re: Volvo MD7B warning lights

Post by Moslund » Tue Jul 25, 2017 4:03 pm

Thank you for answering Peter!

When I look at my manual it looks like all three lamps should be on with ignition but I am not sure.
What you suggest about the alarm control unit being broken seems plausible but the way I read the diagram, the unit just gets a ground when the lamps does (from the temp sender). If that is correct how can the alarm control unit affect the lamp? Maybe i read the diagram wrong..
The lamp receives a + wire on one side, and two - wires on the other. One to the feeler/sender and one to the alarm control unit.
The easy thing would be to replace the alarm control unit and see what happens but it seems to be out of production.

I can't really say if the engine works without problems because I have only had the boat for a week and I´m just a little worried if I´m sailing with an engine that´s overheating.

peterohman
Posts: 24
Joined: Sun Sep 30, 2012 8:24 pm

Re: Volvo MD7B warning lights

Post by peterohman » Fri Jul 28, 2017 10:35 am

I doubt that it shall be on with ignition since it is a simple switch that operates when it exceeds a certain temprature. If the engine is overheated the cooling water will be boiling and the engine temp will exceed 100 degrees, i.e. water dropped on it will also boil.
Have you checked that the thermostat opens as it should?
/Peter

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