R8 fuel gauge sender unit access
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Thread: R8 fuel gauge sender unit access

  1. #1
    Too many posts! JohnW's Avatar
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    Default R8 fuel gauge sender unit access

    The bad news is that the fuel gauge sender, of some years of occasional sulking, seems to have decided to call it a day.

    The next bad news, following my trusty manual, was that I couldn't get the rear parcel shelf trim off because it is held in by seat belt mountings, partly the baby seat from 1977. Those mounts won't come out because the bolt heads are, of course, only accessible from the engine side, that is in front of the panel between fuel tank and engine. This is starting to sound like a Citroen story.

    I don't remember exactly but I don't think I had to take the engine out to install the seat belt mountings. Surely I'd remember such pain. However, I definitely can't get the panel out with the engine in place. This is partly because the 10S head has its temperature warning light switch poking out the back of the head, almost touching that panel. There just isn't enough space to get it out with the cylinder head still on the engine. Hmm. There isn't enough room to unscrew the sender unit either.

    So, getting the old (and surely in need of replacement) trim out with a Stanley knife, I then find the manual is wrong, completely, and there is no access hatch to the fuel gauge sender unit. I'd not expected that, but maybe should have. There is one in my 4CV! Checking the factory parts manual, sure enough no access hatch is shown on Renault's excellent line drawings. Bugger. There are two types of fuel tank, with sender units in different places. I'm not above cutting a hole to get at it, but reluctant.... I'm not 100% sure which tank mine has. Although being a late 1964 car, a late R1130, I suspect it is the later, bigger tank. So I might have to cut two holes, maybe three, to get the right place. I guess a drillhole big enough to get a neat fibre-optic camera in to have a look would answer that question. Even then, would a hole in the parcel shelf floor allow removal of the sender unit and the arm with the float? Don't know....

    My options are:

    1. Forget the fuel gauge and reassemble the car, albeit tidying up the trim professionally and replacing the hopeless old sound-deadening matting.
    2. Start cutting holes
    3. Pull out the whole transaxle, and the fuel tank, to replace the (probably faulty) sender unit.

    Clearly 1. is the pragmatic solution and also I should carry a small spare fuel container. After all, VW beetles were like this for years.

    I'm reluctant to do 2. but the mood might take me sometime!

    3. is quite unacceptable. Next time the transaxle and cross-member is out (it never has been out, ever, mind you) I can easily change the sender unit.

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    The final risk is, of course, that it isn't the sender unit at all. It might be a connection, although I'd put my money on the unit being at fault.

    The good news is that I've found a few things that need a bit of attention in the course of this partial dismantling. So I can keep ahead of them easily.

    Any ideas?

    Cheers

    John
    Last edited by JohnW; 17th October 2015 at 03:01 PM.
    JohnW

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  2. #2
    My Supermodel 63-1092's Avatar
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    4th option, sell me the car cheap and I'll worry about fixing it.
    John
    Александър Кристоф Шанел

  3. #3
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by 63-1092 View Post
    4th option, sell me the car cheap and I'll worry about fixing it.
    They say every man has his price. In this case, my daughter might not speak to me again if I sold the R8 after 42 years. That is a price too high.

    Option 1 looks attractive right at this moment.
    JohnW

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  4. #4
    Fellow Frogger!
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    The senders do wear out the resistive "windings" get worn through
    What's the big deal about dropping the engine and transaxle out
    I have only had an early 8 and it had removable rear panel so you could do it solo

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    JW..Option 2=fail..
    Every day when I wake up I reach up in the darkness with my eyes shut and if I cannot feel anything that resembles a wooden lid I know it will be a good day. No lid today.

  6. #6
    1000+ Posts renault8&10's Avatar
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    There is definitely a hatch on the r1132 shell. I'll take a photo of location just in case you're looking in the wrong spot.
    Even with the hatch off the access is pretty tight, but I did change the sender on the green R8 in situ.

    Are there other tidy up jobs you could do if you pulled the engine?
    After us telling Forzamachi how easy it is, you can hardly baulk at it now?

    Edit - it should be a ridge or two right of the centreline, as you kneel on the back seat facing out the rear window (if it's there).

    KB
    Last edited by renault8&10; 17th October 2015 at 04:32 PM.
    KB


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    Too many posts! JohnW's Avatar
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    Quote Originally Posted by renault8&10 View Post
    There is definitely a hatch on the r1132 shell. I'll take a photo of location just in case you're looking in the wrong spot.
    Even with the hatch off the access is pretty tight, but I did change the sender on the green R8 in situ. Are there other tidy up jobs you could do if you pulled the engine? After us telling Forzamachi how easy it is, you can hardly baulk at it now? KB
    Very funny. I could pull it out of course, but it isn't a priority that ranks at all given the time involved and other things to do.

    I'd really appreciate a photo, that is for sure. I haven't all the trim backing off, but there isn't an obvious hatch that I've found.

    Cheers
    JohnW

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    Too many posts! JohnW's Avatar
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    Quote Originally Posted by 59 Floride View Post
    JW..Option 2=fail..
    I agree. We did do it once, on the Citroen BX floor, as an alterative to huge dismantling to refit one rubber hose! Cut hole, fixed problem, welded up floor. Definitely a fail at one level, but she is a working girl not a show car.
    JohnW

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  9. #9
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by Sherman View Post
    The senders do wear out the resistive "windings" get worn through
    What's the big deal about dropping the engine and transaxle out
    I have only had an early 8 and it had removable rear panel so you could do it solo
    I suspect the float, as it has been getting less keen to return to full on the guage for a few months now. The big removal isn't a big deal other than time taken that could go into more useful things, including sleeping. My cross member has never been removed so some bolts will be a wee bit tight.

    So, take you point of course, but it doesn't appeal.
    JohnW

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  10. #10
    1000+ Posts renault8&10's Avatar
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    John,
    I've edited my post above with photos for you.

    Don't forget, it will be pretty much covered with bitumen paint. So look for an obvious indentation.
    KB


  11. #11
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    Quote Originally Posted by renault8&10 View Post
    John,
    I've edited my post above with photos for you.

    Don't forget, it will be pretty much covered with bitumen paint. So look for an obvious indentation.
    Thanks Kevin. Just what I needed. I have no bitumen paint (R1130) but a bitumen sheet over the whole area, cluttered with seat belt mountings attached to a large piece of steel under the shelf.

    Anyway, you are exactly right. I have a similar panel in the same place - in the only place I hadn't lifted the disintegrating bitumen sheet between the seat belt mount bolts. All four screws undid successfully, revealing the sender unit. Now for the fun!

    I found a sensor wire about to break in the course of trying to get the rear panel out, and in the course of resoldering the tag the nylon line to the oil pressure gauge snapped at the engine end, and the brass sealing nipple has taken 1 1/2 hours to persuade back onto the snipped off line - I can still remember that being difficult in about 1975 when I fitted the gauge. Very tight fit and of course half buried in the engine bay.... Still better it broke when being flexed than fatigue-failed half way to somewhere.

    Bit of water coming through the rear window seal too by the look of it. Recent and no rust happily.

    Cheers, and thanks again.
    Last edited by JohnW; 17th October 2015 at 07:59 PM.
    JohnW

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  12. #12
    1000+ Posts renault8&10's Avatar
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    Glad I could help John. Now the fun starts for you!
    KB


  13. #13
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    Can you not remove the sender from the back of the head then take the head?
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  14. #14
    1000+ Posts renault8&10's Avatar
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    Getting it back in and sealed might be the issue there. I know what John is saying, it is a tight squeeze in there with that setup, a bit like a 12 engine in an R8 or 10
    KB


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    Too many posts! JohnW's Avatar
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    Ah well, some pain later, it is fixed.

    The problem, as suspected, was the death by drowning of the cork float. I modified the float arm and replaced the old unit, keeping the new and second hand spares for the later failure of the resistance unit.

    Calibration of the system? Hopeless. I've done 70 km since a fill-up and it shows only a bit over half full, exactly half full with the new sender unit. Hmm. When nearly new, the gauge only showed 7/8 full when brimming. At least I will know now when it really is empty, as the low level on the gauge corresponds with high resistance (about 500 ohms) at all of the senders. When "full" at the sender unit, the resistance varies from 1.5 to a bit over 5 ohms, depending upon which sender unit I measured up. Hmm again. These were never particularly accurate of course.

    All three of the sender units in my workshop have the same part number on the top (85467 001). However, also in another line (with H246 on all three) there are three different numbers: J3 (old unit), J6 and 12V/6V on the brand new unit and G5 on the old one I've had for years. Any ideas? The old unit is 1.5 ohms and the new unit 5 ohms respectively with the arm in the full position.

    Many thanks for the advice Kevin. It was fairly easy once I'd found my 7 mm x 1/4" drive socket.

    Cheers

    John
    Attached Thumbnails Attached Thumbnails R8 fuel gauge sender unit access-fuel-gauge-sender-unit-exposed.jpg   R8 fuel gauge sender unit access-fuel-gauge-sender-unit-floats.jpg   R8 fuel gauge sender unit access-fuel-gauge-sender-unit-removal-7-mm-bolts.jpg  
    Last edited by JohnW; 18th October 2015 at 01:42 PM.
    JohnW

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    Good result...
    Every day when I wake up I reach up in the darkness with my eyes shut and if I cannot feel anything that resembles a wooden lid I know it will be a good day. No lid today.

  17. #17
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    You can trim the "readings" with the appropriate 5 watt resistors
    I did that on Xantia V6 that I had put Xantia turbo fuel pump in
    ( the pump and sender are integral)

  18. #18
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    Quote Originally Posted by 59 Floride View Post
    Good result...
    Thank you Graham. Beat Option 2, didn't it!

    I hoped Kevin would come through exactly as he did. Gutting the back interior is good too, as I now know I must get the rear window better sealed and will get the rear parcel shelf re-trimmed. I've ordered the new soundproofing too and it is on its way. I found a rare type of tapered lock washer too, so that is now in the stash.

    Trying to get in the other way revealed some things to fix, and they are duly fixed, so a good weekend really. I've even painted the splash guards for the first time in, well, decades, which will improve things.

    She's nearly ready for Griffith 2017 already.

    Cheers
    JohnW

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  19. #19
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    Quote Originally Posted by Sherman View Post
    You can trim the "readings" with the appropriate 5 watt resistors
    I did that on Xantia V6 that I had put Xantia turbo fuel pump in
    ( the pump and sender are integral)
    Good thought for which thanks. I've done that with my temperature gauge as it happens. I need negative ohms though, as the thing is under-reading when practically full. I need to fill it properly before worrying further of course.
    JohnW

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  20. #20
    1000+ Posts alan moore's Avatar
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    If you bend the float arm in the middle so that it sits lower towards the bottom of the tank, it will show full for longer and be closer to correct at half full. Perhaps you can experiment with the gauge reading with varying amounts of float arm travel whilst it is out in your hand, to work out how much bend it needs in the arm to be a more accurate.

    Generally the resistance should be virtually zero at full to give a full scale deflection of your fuel gauge.
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    John,
    Only if you want.............seeing that the old sender unit was more accurate and you were used to its readings, why not use it again?
    I had an identical issue on my car with the soaked float. I did not have a spare unit so I bought a 230V bedside lamp/globe, about 30W and the shape of a candle. The glass part is about 70 -80 mm long and about 25 dia. I'm sure you will know what I mean.
    Then I removed the old cork completely and cleaned the wire arm thoroughly and soldered the globe on to the arm so that it is in the same position as the cork used to be. The globe is vacuum tight and being glass, it should last forever.
    Regards
    Frans,
    Old enough to know better
    Young enough to do it anyway.

  22. #22
    Too many posts! JohnW's Avatar
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    Thanks Alan,

    That's a good idea and I'll play once I have the car full of petrol. At fully "up" the sender unit has about 1.5 ohms (and the new one a few more ohms than that). So I guess I need to start by connecting it when out of the tank (and be careful regarding sparks and playing. At least with everything inside dismantled, this is relatively easy. I'll let you know how I get on.

    Cheers

    Quote Originally Posted by alan moore View Post
    If you bend the float arm in the middle so that it sits lower towards the bottom of the tank, it will show full for longer and be closer to correct at half full. Perhaps you can experiment with the gauge reading with varying amounts of float arm travel whilst it is out in your hand, to work out how much bend it needs in the arm to be a more accurate.

    Generally the resistance should be virtually zero at full to give a full scale deflection of your fuel gauge.
    JohnW

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  23. #23
    Too many posts! JohnW's Avatar
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    Thanks Frans.

    I'd not thought of the light bulb idea. I'd say you get the prize for the lateral thinking, and not for the first time! My thoughts were the same actually, as I've kept the old sender unit and bent the end to hold the plastic float that came attached. So I am using the old sender unit. As I replied to Alan (you two should meet!) I will play further once I've filled it with petrol.

    Cheers

    John

    Quote Originally Posted by Frans View Post
    John,
    Only if you want.............seeing that the old sender unit was more accurate and you were used to its readings, why not use it again?
    I had an identical issue on my car with the soaked float. I did not have a spare unit so I bought a 230V bedside lamp/globe, about 30W and the shape of a candle. The glass part is about 70 -80 mm long and about 25 dia. I'm sure you will know what I mean.
    Then I removed the old cork completely and cleaned the wire arm thoroughly and soldered the globe on to the arm so that it is in the same position as the cork used to be. The globe is vacuum tight and being glass, it should last forever.
    Regards
    Frans,
    JohnW

    Renault 4CV 1950 (R1062)
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    Quote Originally Posted by JohnW View Post
    Thanks Frans.

    (you two should meet!)

    Cheers

    John
    Now that is an idea worth bottling, imagine those two go-fast Renault brains left to their own devices..the mind boggles what might eventuate from that...
    Every day when I wake up I reach up in the darkness with my eyes shut and if I cannot feel anything that resembles a wooden lid I know it will be a good day. No lid today.

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    Quote Originally Posted by 59 Floride View Post
    Now that is an idea worth bottling, imagine those two go-fast Renault brains left to their own devices..the mind boggles what might eventuate from that...
    One must visit the other, or both! I am in awe, personally.
    JohnW

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