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Location:
Ipswich
Registered:
May 2002
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Oil pressure sender and idiot light?
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Mon, 22 March 2004 11:58
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I've got a 4AGE, and I want to run an oil pressure gauge, oil temp gauge and the oil pressure idiot light (red light that comes on when low pressure).
Instead of running 3 separate senders, a friend of mine mentioned to me he's heard of a way to make the idiot light work using the oil pressure sender? Something about (he wasn't sure either) using some sort of diode that only allows current through after a certain voltage?
Does anyone know how to set this up?
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Location:
Ipswich
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Mon, 22 March 2004 12:00
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Did a quick search, I think it's called a Zener diode?
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Mon, 22 March 2004 13:08
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Yep, it is. A Zener will only conduct above a certain voltage, consult an electronics book for more details, or just use a combined idiot light/gauge sender 
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Location:
Ipswich
Registered:
May 2002
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Location:
Terrigal
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Mon, 22 March 2004 23:27
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I'm very interested in this, currently only have the gauge which is useless really as you can't always be watching it unlike a light that warns you.
At a guess 15psi you'd want the light to come on at?
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Location:
Ipswich
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Tue, 23 March 2004 00:11
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Actually, stuff trying to pressurise the sender... Just hook up a variable resistor to the signal wire and change resistance until you get the pressure you want it to come on at, and then check that voltage...
Now the only question is what pressure you'd want the idiot light to come on at... Might have a look at the 4AGE book when I get home and see what the normal operating pressure is... Unless someone on here knows it off the top of their head? 
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Club Member
Location:
sydney
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Tue, 23 March 2004 03:14
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60-80 psi from memory, drops as low as 20-25 at idle
use a potentiometer to dial up your required resistance depending on what your doing.. i.e track or road. obviously on the track youd want your pressure to stay nice and high when your at high rpm, cause if it lets go at 6000rpm by the time the pressure drops to around 15psi to turn the light on your engine will allready be on its way to rebuild city.
just find the voltage range of the sensor and buy a potentiometer (with or without an added resistor) to suit the range
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Location:
Ipswich
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Tue, 23 March 2004 03:30
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So... For normal driving 15psi is a reasonable pressure to have the light come on?
Trying to understand what you mean with the potentiometer, I'm guessing to run a potentiometer and the zener diode (of a much lower voltage breakoff) and set the potentiometer high when driving around normally so that the light will only come on at low (ie 15psi) pressure, and then set the potentiometer high for trackwork so that the light will come on at a higher (ie 40psi maybe) pressure?
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Location:
Sydney
Registered:
February 2003
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Re: Oil pressure sender and idiot light?
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Tue, 23 March 2004 09:27
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why not just use a t-piece where the sender mounts to the block?
if its anything like the old 5ME, a t-piece with the factory sender and the gauge hookup will do fine.
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Club Member
Location:
sydney
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Tue, 23 March 2004 10:12
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because T pieces like to snap off leaving a small section in the block under even mild vibration 
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Location:
Ipswich
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Tue, 23 March 2004 14:06
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There is no factory sender  Plus I've got oil pressure and temp I want to hook up, would prefer not to also have to run another sender for idiot light, if I can use the oil pressure sender that would be flash
I'm thinking of running a T-piece, mount oil temp sender (small) on one side, and remote mount the oil pressure sender (big). Hopefully with little stress on it it won't crack or break...
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Location:
Terrigal
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Tue, 23 March 2004 23:44
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Yeah I had a T piece and broke. was a huge pain to get the bit out of the block. Had to get a specalist come and drill it / tap it out and had the headache of wondering if any metal filings fell in inside. Would never run one again.
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Location:
Melbourne
Registered:
May 2002
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Registered:
July 2002
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Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 00:28
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If you want to accurately set an "idiot light" you should look in to a more useful device called a comparator. There are many cheap kits (under $20) in Jaycar and DSE based on these (the LM339 is a common one). Examples of these kits are low fuel warning lights, over temp warning lights etc. most of the kits show how to adapt the kit to another application. A little more elegant than chucking a zener diode on it and due to the high input impedence of a comparator, it wont affect your analog guage at all.
I am pretty sure the VDO type you have will be voltage output.
In a 4AGE with idiot light only a few seconds of cranking is enough to extinguish the light so one would have to presume that it is in the range of 5-10 psi.
With the above circuit, you could also have two settings as suggested, selectable with a switch.
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Location:
Ipswich
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 04:12
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c2888: Thanks heaps for that link, might run that setup
Anthony: Thanks for that... Would the Jaycar kit KA1778 work? That's the closest I can find on their website...
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Location:
Brisbane
Registered:
February 2003
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Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 04:23
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fwiw: check the block near the poil-pressure sender as there might be another take-off point.
My 18R block had a steel, screw-in plug blocking a hole just below the oil-pressure sendor. Both ports opened up to the same oil gallery.
So i have the oil pressure sensor in the lower hole and the upper hole feeds the oil-cooler which feeds cool oil to the turbo.
maybe your block has an alternate port?
Also, i've seen thick, pipe-like brass fittings that have the same female threaded hole and one half-way down the 'pipe' so you could run a hose to this fitting to remote it and have two holes. I'll see if it's still in my collection of plumbing shit when i get home - tho i do recall stuffing it when trying to clean the threads out with a cheapo tap-n-die set.
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Club Member
Location:
sydney
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 05:47
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I have seen the remote T piece set up before and to me its just another easy failure point. Although PVC tubing is fairly rugged it is not uncommon for the connection points to fail, leaving a nice big oil spray around the engine bay
personally id just run a second wire off the factory pickup to the idiot light.
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Location:
Ipswich
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 05:54
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Michael: I see the point you're making. However, for me it's not as simple as running a second wire off the factory pickup point. If you read the above posts you'll see what I mean.
For a start, my sender doesn't screw into the factory pickup (different thread) so I'll need to use an adaptor anyway. Secondly I have 2 senders to feed - temperature and pressure. Therefore I either need two seperate points on the block to feed from, or run a T-piece - remotely or otherwise.
Does anyone know what the other hole in the block is (next to the factory oil pressure sender)? If I'm not mistaken (I briefly saw it the other day, didn't investigate) there is a bolt through it. Does it lead to the same oil gallery? If so I might be able to put the temp sender on there with an adaptor (it's only small and light after all) and just run a flex line from the factory point to the oil pressure sender, remotely mounted. That way I don't need to run a T-piece.
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Club Member
Location:
sydney
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 06:34
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there are plenty of places to pick up a second line.. goto Bill Sherwoods website and look for the oil flow diagrams , i think club4ag has them too and you can easily see where the other pickup points are.. you can also drill and tap at a couple of points.. youll see the flat machined spot where to do it on the block when you cross reference the pictures
you can buy short adapters that fit the sender so that the weight is still close to the block.. the other option is to use a T piece but make a supporting brace off the block to help stabilise it.. if done correctly it can help.
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Location:
Ipswich
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 06:39
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Ta for that, I'll go look for those oil flow diagrams tonight...
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Location:
Adelaide
Registered:
May 2003
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Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 06:52
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That bolt next to the oil sensor is the coolant drain plug, not a hugely great idea to loose that.
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Location:
Ipswich
Registered:
May 2002
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Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 07:08
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Ah dang. Oh well, thanks for the info, saves me taking it out and finding green stuff instead of black stuff
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Location:
Sydney
Registered:
May 2002
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 Re: Oil pressure sender and idiot light?
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Wed, 24 March 2004 11:08
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I had this problem when I changed the dash for one with extra instrumentation with the new electric oil guage I still wanted the idiot light as well. I found the voltage at the sender was lo with the motor stopped and went up over a volt as engine started and oil pressure went up. I used this voltage to switch on a small transistor that disabled another pulling on the idiot light, so that when oil pressure low or non-existant idiot light came on.
Cost of bits close to zero.
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