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300Tdi Coolant Level Sensor
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Mud Obsessed


Joined: 06 Feb 2006
Odometer: 4337
Location: Norfolk


1995 Land Rover Defender

PostPosted: Tue Nov 14, 2006 6:32 am    Post subject: 300Tdi Coolant Level Sensor Reply with quote

As suggested, this is a new thread to bring together some of what has been learned in the Discovery Coolant Level Sensor thread.

Synopsis:
The Range Rover has a coolant cap which incorporates a level sensor to warn the driver when there is coolant loss. This is a very useful feature on the 300Tdi engine because the water pump is mounted so high that even a little coolant loss can result in the pump running dry and catastrophic engine failure.

After much discussion we now think that the RR coolant cap has a magnetic reed-switch which is closed when the coolant level is correct and wired in series with the reed-switch within the coolant cap is a resistor of 560 or 680 ohms. This means that we need to indicate a fault (low coolant) when the switch is OPEN and the switch can not supply enough current to reliably operate the coil of a relay. Simple circuits (described on Difflock and elsewhere) which use a relay will not work unless a very sensitive relay coil is used.

Don has found a found a circuit module here which looks like it could act as the interface between the coolant cap and whatever warning device is needed. I have lashed up a different circuit to do a similar job using an opto-isolator. However neither of us have the coolant cap to do a proper test.

We are still looking for the part number of the RR coolant cap.
--
Tim.

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reedx
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PostPosted: Tue Nov 14, 2006 7:04 am    Post subject: Reply with quote

Tim, is this it (from John Craddock), or is the cap a separate part?

Part Number : PRC7925
SENSOR LOW COOLANT LEVEL RANGE ROVER VIN
NO. GA ON
£31.00

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Colin Reed
www.REEDX.net/landrover
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dpcwright
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PostPosted: Tue Nov 14, 2006 9:10 am    Post subject: Reply with quote

According to my parts book this is the cap used on both diesel and V8 engines.
David Wright
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Mud Obsessed


Joined: 06 Feb 2006
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1995 Land Rover Defender

PostPosted: Tue Nov 14, 2006 9:20 am    Post subject: Reply with quote

Thanks Colin and David,
I have ordered one from my local dealer (list price is £40 with the VAT).
I wouldn't normally "waste" so much on something I could get from the breakers or make myself but this seems the only way to sort out the problem once and for all.
--
Tim.

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mr_e
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PostPosted: Tue Nov 14, 2006 8:06 pm    Post subject: Reply with quote

Hi Tim,

Sorry I didn't know you were waiting on the cap part number, I thought you had read my original post, (300tdi may seriously damadge your wealth) where down the line I furnished the thread with all the part numbers for my set up.
Thanks for the infomation on resistance, I understand the coil resistance now.
I thought the cap resistance was due to a poor contact conection Rolling Eyes
I think I made the right choice becoming a mechanical development engineer Smile
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Mud Obsessed


Joined: 06 Feb 2006
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1995 Land Rover Defender

PostPosted: Wed Nov 15, 2006 9:08 am    Post subject: Reply with quote

mr_e wrote:
Part number for cap is PRC7925 £33.92 +vat ...

You did indeed give the part number in this thread and I missed it, probably because at that time I was thinking about doing my own design of switch.
mr_e wrote:
I think I made the right choice becoming a mechanical development engineer

As it happens in the end the solution to the problem looks to be simple enough. It has seemed more complicated because neither Don or myself have had a switch to look at which means we have been speculating based on second-hand information. As always, contributions from everyone are useful, but it sometimes takes a bit of effort to sort the wheat-from-the-chaff.
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Tim.

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mr_e
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PostPosted: Fri Nov 17, 2006 6:13 pm    Post subject: Reply with quote

Hmm, whats it the black box Tim???
Have you got your cap switch yet?

Regards

Mark....
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Mud Obsessed


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1995 Land Rover Defender

PostPosted: Fri Nov 17, 2006 6:24 pm    Post subject: Reply with quote

I picked up my Range Rover float switch (part number PRC7925) today but haven't yet had time to check it in the Defender header tank. I can confirm that my one has a reed-switch in series with a 680ohm resistor.
The picture tells the story ...
The white plastic float supports a ring magnet. The float has about 10mm of free movement before hitting a stop. As it rises up the shaft the reed switch closes. The assembly is sealed so I can't dismantle it without damaging something, and at £40 I'm not going to.

So, 680ohms between the contacts means all is well, whereas an open circuit means low water.

Mike has a test circuit and will report back in the fullness, if all is well I will post the circuit here (it is very simple).
--
Tim.

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mmgemini
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PostPosted: Fri Nov 17, 2006 6:48 pm    Post subject: Reply with quote

Yes little black box with wires sticking out arrived today.

If it's fine I'll fit it tomorrow.

That Range Rover float switch is different to mine.

I'd like to run the vehicle for a few days just to make sure.

Peter.
Could this post be nailed to the top untill all the tests have been done please.

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mmgemini
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PostPosted: Fri Nov 17, 2006 8:52 pm    Post subject: Reply with quote

Tim
You have a PM

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110cswdefender
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Joined: 30 May 2004
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PostPosted: Fri Nov 17, 2006 9:02 pm    Post subject: Reply with quote

Hi all.

Interesting to see the photo of Tim's switch.

Mine (which is marked 'Land Rover', has no internal resistor and is 'on' when the float is down') is almost identical, but the section that is black on Tim's is white on mine, and that section appears to be a little shorter on mine.
(The total height of mine is 115mm).

Don
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Mud Obsessed


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1995 Land Rover Defender

PostPosted: Sat Nov 18, 2006 1:01 pm    Post subject: Reply with quote

My cap is nearly 160mm long, it physically fits in the header tank and the float is free to move.

The tank normal coolant "full" level is 84mm below the gasket surface of the cap and my switch operates with when the float falls to 118mm below the cap gasket, so a 34mm loss of coolant will trigger the switch.

I have done a test drain of the header tank; the switch tripped after the loss of about 850ml of coolant. However, because of the shape of the header tank and the location of the drain I could only drain another 100ml, so it is a fairly close call. In the real world, I don't think this is a problem because movement and vibration will probably allow more coolant to be withdrawn or at least jiggle the float switch to trip earlier.
Nevertheless, I would like to raise the trip level a bit. Moving the position of the magnet and increasing the travel of the float doesn't look too difficult, this could raise the trip level by 10-12mm.

I'm glad everything doesn't turn out to be this time consuming.
--
Tim.

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110cswdefender
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Joined: 30 May 2004
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PostPosted: Sat Nov 18, 2006 2:43 pm    Post subject: Reply with quote

Hi all.

I just did a little investigation of my cap.... Shocked

I found that by grasping the screw cap in one hand and pulling the lower section (with a bit of a sideways waggle) the switch assembly popped out quite easily.
Unfortunately I don't have a camera with macro capability, but will attempt to describe what is in front of me.

The top of the cap (the bit with the spade connectors) has a strip of metal that goes down towards the magnet. The reed capsule is soldered to the bottom of this, and a wire from the lower end of the reed capsule goes up to the other spade connector. (the reed capsule is N/O).

Speculation Exclamation : presumably the magnet on the 'standard' cap is aligned with the reed contacts when the float is 'high' and falls below the contacts when the float is low, thus releasing the contacts. IF the reed could be lowered a little the maybe switching action could be reversed ?.
Maybe the resistor could also be shorted ?.

Better yet... my cap is definitely NOT a figment of my imagination, surely someone can identify the part number.

Don.

******* DISCLAIMER.. Arrow I AM NOT ENCOURAGING ANYONE TO TAKE THEIR CAP APART. *******
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mmgemini
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PostPosted: Sat Nov 18, 2006 3:11 pm    Post subject: Reply with quote

YIPIEeeeeeeeeeeeeeeeee.................

The little black box works.Well while the car is sitting still LOL

It's cold and getting dark and I still have some soldering to do.

The batteries in my camera are flat so I've put them on charge hoping that we migh have some pictures tomorrow.

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mr_e
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PostPosted: Sat Nov 18, 2006 4:43 pm    Post subject: Reply with quote

Hi There,

One thing I've found with my set up is the need to fill header tank about 20mm higher than normal, to stop nuisance tripping if braking hard or cornering a bit enthusiasticly Wink
Looking forward to seeing the end result.

Regards

Mark.......
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mr_e
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PostPosted: Sat Nov 18, 2006 4:50 pm    Post subject: Reply with quote

Hi Don,
Just seen this on E-bay


http://cgi.ebay.co.uk/Vauxhall-Opel-Carlton-Sen...dZ1QQcmdZViewItem

Is it the same as yours?

Mark........
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110cswdefender
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PostPosted: Sat Nov 18, 2006 7:03 pm    Post subject: Reply with quote

Hi Mark.

It looks identical, based on the single e-bay photo.

Mine is definitely marked 'Land-Rover' by the connectors, but was made by VDO.

I am not sure that mine will work properly if the coolant level is maintained at the 'official' level, I haven't actually tried mine in the vehicle (yet).
I don't see why the header tank couldn't be maintained at a higher coolant level Question , but I invite other opinions.
The level doesn't seem to vary a great deal between cold and hot in my experience.

It may have the same electrical characteristics as mine or IT MAY NOT.
It is also possible that the two pressure valves (one for in, one for out) that are built into the cap may operate at other pressures.

May contain nut traces, the value of your investment may go down as well as up... please add any other disclaimers that seem appropriate ! Wink .

Don
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Mud Obsessed


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1995 Land Rover Defender

PostPosted: Sat Nov 18, 2006 8:16 pm    Post subject: Reply with quote

Don,
Mine is also made by VDO and labelled Land Rover and is of exactly the same construction as the eBay picture, with separate in and out pressure valves. From the plastic mould marks it looks as if the central portion of the stem can be made in different lengths.

I would be a bit concerned about raising the coolant level by much. I suspect if it is raised more than an inch or so above the cold level it will simply vent. However, I can't see that it will cause any harm (as long as the vent works) to try it and see.

I have just sketched my circuit which I'll post shortly.
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Tim.

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Mud Obsessed


Joined: 06 Feb 2006
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1995 Land Rover Defender

PostPosted: Sat Nov 18, 2006 8:48 pm    Post subject: Reply with quote

Since Mike has confirmed my circuit works for him, here it is for anyone who wants to make the same.

My bit is in the central dashed rectangle, there are only 5 components. The design is not optimised, it was simply made from bits in my 'junk-box'. I've drawn it more-or-less as you would see it rather than in proper schematic format. The input from the cap switch is on the left, the output to a lamp/buzzer is on the right and power at the top, ground at the bottom. I used an opto-isolator, but it would be equally acceptable to use a small-signal NPN transistor with a base current limiting and pull-down resistors. The smart FET is a tough device and requires no further protection even when driving inductive loads, it will easily handle more than 5 amps, so you could drive a VERY LOUD sounder!

The +12V connection should be to a fused ignition live circuit. Do not connect directly to the battery as there is a small current drain all the time.

Operation:
When the coolant level is correct the cap switch is closed, allowing current to flow through the green LED (to show system is OK) and through the opto-coupler. The output of the opto-coupler is used to short the input of a smart FET to ground keeping it OFF.
When the coolant is low, the cap switch opens thus switching the green LED off; this allows the smart FET turn ON via the 10Kohm pull-up resistor.

I have tested the circuit under normal automotive fault conditions, reversed battery (-12V), double battery (+26V) and also with the cap switch input connected directly to +12V. If you were using a cap switch without a built-in resistor OR wished to miss out the green LED, I suggest increasing the 680ohm resistor to at least 1Kohm.

In the bottom left is a little extra test circuit which Mike has tried. Pressing the 'normally-open' push switch should light the auxiliary green LED AND sound the coolant alarm.

The parts are available from RS Components (RS number shown), but there are plenty of alternatives, the circuit is not critical.
SmartFET: VNP10N06 (RS:313-2986)
Opto-coupler: ISP817XB (RS:453-0640)
Green LED (RS:247-1735)

This information is offered in good faith, but as usual I'm not accepting any responsibility for how you use it!
--
Tim.

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Last edited by :) on Sun Nov 19, 2006 6:14 am; edited 1 time in total
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mmgemini
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PostPosted: Sat Nov 18, 2006 9:26 pm    Post subject: Reply with quote

I think we should all say a very big thanks to Tim.
This is his bread and butter and he has given this for free.

For those who don't want to have to press a button each time they start the car and don't want a green LED on all the time.I'm sure that you could fit a timer relay instead of the push switch.
I took my Defender out in the dark and the green LED didn't bother me while driving.

Comments please Tim.

Again Tim THANK YOU VERY MUCH.

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reedx
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PostPosted: Sat Nov 18, 2006 9:44 pm    Post subject: Reply with quote

Tim, if possible could you pm or email me a larger copy of your diagram? I'm not sure if it's the forum maximum image size causing a problem but I can't make out some of the detail.

P.S. I looked up the RS part numbers you quoted. I like the LED manufacturers name Wink

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Colin Reed
www.REEDX.net/landrover
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:)
Mud Obsessed


Joined: 06 Feb 2006
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1995 Land Rover Defender

PostPosted: Sun Nov 19, 2006 6:03 am    Post subject: Reply with quote

Colin,
For others: the LED manufacturer's name which Colin is referring to is a typical Chinese one "Kingbright"; another one which used to amuse me was "Lucky Goldstar", but they renamed themselves just LG - who, I expect, most people have heard of.

reedx wrote:
I'm not sure if it's the forum maximum image size causing a problem but I can't make out some of the detail.

Err, probably more likely my scribble (I've had severe toothache recently, so I'll blame that then) ...
I resampled the above to 800 pixels, so as not to cause the 'wide-page' phenomenon, but didn't do a good job, I'll see if I can replace the image with a better one and I'll email you a copy of the original.

Anyone else who would like a better image please PM me with your email address.
--
Tim.

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mr_e
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PostPosted: Sun Nov 19, 2006 10:31 am    Post subject: Reply with quote

Hi Tim,

Looks good Very Happy Thanks for doing this for your fellow landy lovers.
I've sent you a PM with my e-mail address if you could send me a copy so I can get my one made up. Will I need some more circuit board? and roughly how big is it, as my water proof box is 3"x5"x 2.5" deep Confused

Regards

Mark.......

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mmgemini
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PostPosted: Sun Nov 19, 2006 11:26 am    Post subject: Reply with quote



Range Rover Classic sensor for brass header tank.




As fitted to me Defender

]



Temporary fitting to top of dash.How temporary remains to be seen Laughing

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Mud Obsessed


Joined: 06 Feb 2006
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1995 Land Rover Defender

PostPosted: Sun Nov 19, 2006 2:08 pm    Post subject: Reply with quote

Based on the PMs I received this has caused a fair bit of activity.

To answer some queries:
I didn't solder the components onto a board. Instead I stuck them together as a 3D wire-frame and then (to make sure nothing moved) I encapsulated it with a two-part epoxy potting compound. I'm sure it could be mounted on a bit of veroboard if desired.

The potting box I used is equivalent to RS:509-024 and is 30x20x15mm in size. The encapsulant is equivalent to RS:199-1402.

I didn't really intend the green LED I mounted on the box to be on permanent show, it's more of an installation/diagnostic check. If you want to change the brightness either fit a low current LED or reduce the resistance of the 680ohm resistor.
--
Tim.

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john
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PostPosted: Mon Nov 20, 2006 9:42 am    Post subject: 300 TDi coolant switch Reply with quote

I can't be the only one surely. Having followed this post through all its trials and tribulations it seem that the problem is now solved. however, for all us electrical novices is there going to be any easy way out, because the circuit diagram shown is just gobledygook to me. I am now so concerned that I am driving round with one eye constantly on the temp. gauge. Is there going to be some kind soul who may put some of these devices together for a few beers? Sad
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discoverytdi
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PostPosted: Mon Nov 20, 2006 9:53 am    Post subject: Reply with quote

Same with me John, green to brown brown to green blue to bit's Brick wall
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mmgemini
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PostPosted: Mon Nov 20, 2006 1:28 pm    Post subject: Reply with quote

John.
The standard temperature gauge will hardly shew the temperture rise that tells you of the loss.
Why do you think I paid all that money for a proper temperature gauge.

I don't drink beer Twisted Evil

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john
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PostPosted: Mon Nov 20, 2006 5:10 pm    Post subject: 300 TDi coolant level sensor Reply with quote

Thanks Mike but I think you missed my point. Whilst I am a qualified engineer in things mechanical, electrics just ain't my forte. At the moment my temp. gauge as fitted is all I have to rely on, be it acurate or not. Which is why I asked the question, is anyone with the knowledge likely to put some of these units together for us non sparky types (please) or do I have to go to evening classes to get a qualification in auto electrics.
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110cswdefender
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PostPosted: Mon Nov 20, 2006 7:21 pm    Post subject: Reply with quote

Hi all.

I think that the relay module that I identified earlier would probably do the job AND would be within the capability of most people, but I'm afraid that I don't have either a 'standard' cap switch or the relay module, so can't be SURE that it would work.

The module has screw terminal suggestions, I would recommend soldered connections for reliability.

Don
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