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Old 15-09-2015, 02:31   #1
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Gauges

Hi there;
I have a single cyl. BMW D12 engine in my boat. The standard dash supplied by BMW is equipped only with idiot lights - those being: Oil pressure, Charging and Engine temp.
I'm most interested to know if an Hour meter can be added, and if so, what kind and how to wire it in to the dash system?
Maybe the latter information might be in the product instructions???
I believe there are two types available, those that register as soon as the ignition is "ON" and then the other type that is wired somehow to the engine and is REAL-TIME engine hours, that is only when the engine is running.
I can see the first one would probably be easy to install as it only needs a hot wire from the ignition, but the second one might require a pressure switch of some kind or???
Anyone familiar with this type of addition?
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Old 15-09-2015, 04:22   #2
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Re: Gauges

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Originally Posted by Sailorbob8599 View Post
Hi there;
I have a single cyl. BMW D12 engine in my boat. The standard dash supplied by BMW is equipped only with idiot lights - those being: Oil pressure, Charging and Engine temp.
I'm most interested to know if an Hour meter can be added, and if so, what kind and how to wire it in to the dash system?
Maybe the latter information might be in the product instructions???
I believe there are two types available, those that register as soon as the ignition is "ON" and then the other type that is wired somehow to the engine and is REAL-TIME engine hours, that is only when the engine is running.
I can see the first one would probably be easy to install as it only needs a hot wire from the ignition, but the second one might require a pressure switch of some kind or???
Anyone familiar with this type of addition?
Oil pressure switch is sometimes used; either a second switch (normally open) or if using the existing one (most likely a normally closed), then a relay can used to get a normally open function.
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Old 15-09-2015, 05:48   #3
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Re: Gauges

Most "Hobbs" meters use an oil pressure switch to supply the ground, that way of course the meter is running only when there is oil pressure.
All kinds of Hobbs meters are available inexpensively, I get mine off of Amazon.com, I even put on on a Honda generator, wired it into it's battery charging terminals, when it's making electricity, the meters running.
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Old 15-09-2015, 06:17   #4
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Re: Gauges

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Most "Hobbs" meters use an oil pressure switch to supply the ground, that way of course the meter is running only when there is oil pressure ...
Exactly.
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Old 15-09-2015, 19:56   #5
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Re: Gauges

Thanks for all the responses folk, unfortunately the BMW D12 engine has neither an oil pump or even a filter. It relies on the old "splash" system which saves on filters for sure ... so I guess it will have to be an electric meter, that will be activated whenever the ignition switch is in the ON position.
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Old 15-09-2015, 21:44   #6
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Re: Gauges

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Originally Posted by Sailorbob8599 View Post
Thanks for all the responses folk, unfortunately the BMW D12 engine has neither an oil pump or even a filter. It relies on the old "splash" system which saves on filters for sure ... so I guess it will have to be an electric meter, that will be activated whenever the ignition switch is in the ON position.
Hmm... something doesn't jell here, in your first post, you described the engine as having an oil pressure idiot light.

Assuming for a moment that is does actually have such a light, this light will illuminate when you initially turn the key on and will extinguish once oil pressure is developed.

If so, I strongly suspect it will have a normally closed oil pressure switch that switches a ground to the idiot light. That is, there is a ground present until oil pressure is developed. In this case, the Hobbs meter circuit as described A64pilot and endorsed by Gordmay will be inappropriate. In this instance you will either have to add a normally open switch to the engine or use a relay to reverse "the sense" of the existing switch so that a relay contact becomes the normally open contact to activate the Hobbs meter.

Quite straightforward, the positive side of the relay coil goes to the key positive and the negative side of the coil goes to the existing oil pressure switch. Thus both the idiot light and relay operate in parallel. Once oil pressure is reached the light extinguishes and relay relaxes. A normally closed contact on the relay then switches a ground to the Hobbs meter. The positive side of the Hobbs meter is feed from the positive of the key switch so that the only time the Hobbs meter is activated is when the key is on and oil pressure is present.

Of course, you initial post may be in error and there really is no oil pressure in the engine; but I got to say, I haven't seen a diesel engine without an oil pump / oil pressure except at antique farm engine display days
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