'73 SM Coolant Leak
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Thread: '73 SM Coolant Leak

  1. #1
    Tadpole
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    Default '73 SM Coolant Leak

    Hey all - I have a 3 litre SM - which has been running superbly the past few months.
    However I have a coolant leak and I can't find it...
    Here's what happened:

    1. 1 month ago, the interior windows started getting white haze on them over a couple days of driving - this is still happening which is really weird. This may be completely un-related.
    2. 2 weeks ago, the heater stopped working - it gets chilly in the morning here in San Francisco! Now it won't come on at all - the air con still works fine.
    3. About the same time I noticed the coolant low and topped it up.
    4. Last Thursday the leak had emptied the expansion tank - I topped it up on the way to work -and 90 miles later it's gone. It takes about a litre to top it up again.

    So - the annoying thing is that there are no apparent leaks under the car hot or cold and no wet carpets - nothing. I've made a video of the back of the engine and there's maybe a hint of a leak from the hole below the water pump cover that is in the end cover casting.

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    https://www.youtube.com/watch?v=uCizaz5AD6U

    Any ideas? I'm going to take the driver side cover off the dash this weekend to look at the thermo valve - I'll post a video of that too..

    thanks!

    John

  2. #2
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    Just a little general knowledge - true for any car.

    1. Vinyl polishes (eg ArmourAll) will volatilize in hot sun and create deposits inside windows - so probably unrelated. OTH, glycol does leave a white residue when it evaporates...

    2. If heater stops working, stop immediately and investigate. Most likely cause is low coolant - without hot fluid flowing, you get no heat.

    3. When level has been so low as to stop heater working, all but the most basic cooling systems will need bleeding - there are likely to be air bubbles trapped in your cooling system.

    4. If you can't locate a leak, think internal - ie blown/leaking had gasket. Coolant can be drawn into one or more cylinders and be quietly evaporated. In this case you may notice more steam than usual from exhaust while engine is warming up. Basic checks - remove spark plugs - if one (or more) plugs are very clean, this can be caused by steam cleaning . Do a compression test while plugs are out.

    Cheers

    Alec

  3. #3
    Real cars have hydraulics DoubleChevron's Avatar
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    Does it have a plastic header tank .... Make sure the tank itself isn't split as well. A tiny crack in a hose that will only spray a fine mist of coolant under pressure (but not leak when there is no pressure) is exceedingly difficult to find..... but will also leave you with constant coolant loss.

    seeya,
    Shane L.
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  4. #4
    Tadpole
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    Thanks Armadillo - I'll check the plugs at the weekend...and get a pressure test on the system too...

  5. #5
    Fellow Frogger! marc61's Avatar
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    The brass header tank is similar to the DS EFI one and they can spring a leak and need brazing up. If the clamps on all of the water hoses are tight, try adding some K Seal, Radweld or similar to the water as it may just be a small hole somewhere.
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
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  6. #6
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    I would be looking at possible heater core leak. Any moisture inside vehicle ? Noticed any coolant odours inside car?

    Cheers
    Andrew

  7. #7
    Fellow Frogger! citroenthusiast's Avatar
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    If you suspect a heater core coolant leak (coolant smell in the cabin) remove the driver's side bolster (don't forget the hidden nut behind the three-gauge cluster) and check for wetness around the heater valve. The heater core is very robust, so if you have a coolant leak at the heater core, it is probably at the valve.

    The stain around the weep hole at the top of the engine is troubling. Water weeps out of that hole only if the lower weep hole is occluded. That means water is/was accumulating between the water pump seal and the jackshaft oil seal, forcing water out of the top of the engine, so you MUST clear the obstruction in the lower weep hole to restore proper function. This can only be done from below.....

    '73 SM Coolant Leak-water-pump-weep-hole.jpg



    A slight wetness from the lower water pump weep hole at the back of the engine is normal, as long as it is not a stream of water, which indicates a failed water pump seal. How long have you had the symptoms? Have you changed anything in the cooing system, like the radiator cap? Changing to a cap that has more than 2psi rating will cause the MKI water pump seal to become the pressure relief valve so you will lose coolant every time the engine heats up.

    Further explanation here: http://www.citroen-sm.org/wiki/image..._seals_ABX.pdf
    Last edited by citroenthusiast; 28th June 2018 at 02:56 AM.
    JohnW likes this.
    Cheers,
    John T.

    54 TAV Legere; 61DS19 LHM BVH (son's); 71DS21 BVH; 73SM 3.0; 73SM EFI (Megasquirt); 73SM 3.0 (other son's)

  8. #8
    Tadpole
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    Thanks John - no changes to the water system since I got the car last September - the cap looks fairly new... The leaking from the weep hole in the video is from the upper part of the rear cover - just below the water pump - the very hole you marked in your photo. I've cleaned it off and we'll see if any more comes out.

    I've done 200 miles this week and of course the leak has stopped! Still no heat out the heater though.

    No smells in the car of coolant. I took the left hand bolster off today and all looks like brand new - there's slight rust on the valve top cover - but that could be 30 years old!

    Apart from the coolant getting everywhere - is it OK to remove the hoses and the valve from the heater core and try and free up the valve off its seat with gentle persuasion through the inlet hole?
    '73 SM Coolant Leak-fullsizeoutput_3d73.jpg'73 SM Coolant Leak-fullsizeoutput_3d72.jpg'73 SM Coolant Leak-fullsizeoutput_3d74.jpg

    Also checked the plugs - and none of them steam cleaned! Which is good I suppose. I changed the plugs Sep 2017 at 72k miles - and now just turned 76,200 miles.

    '73 SM Coolant Leak-img_3594.jpg

    John
    Nothing to see here...

  9. #9
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    That plug is a beautiful sight !

  10. #10
    1000+ Posts Ken W's Avatar
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    The steel pipes that come through the firewall can rust up badly. Maybe some rust has come loose and blocked up the heater radiator. Are you getting any heat in the pipes to the heater valve? Be very careful with the seal on the valve as most of them these days do not shut off properly and you end up with the heater on all the time after you have fiddled with them. But it sounds like you have to check if there is coolant flow through the heater matrix.

    Cheers, Ken

  11. #11
    Tadpole
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    I'll check heat to the inlet pipes in 2 weeks - off to China tomorrow for work, so more updates after the 14th....
    Nothing to see here...

  12. #12
    Fellow Frogger! citroenthusiast's Avatar
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    Failed-closed is a very common problem with the SM heater valve. The connection between the pull-off spring and the valve fails (the plastic finally cracks), which means the valve stays closed under the pressure from the closing spring.
    Cheers,
    John T.

    54 TAV Legere; 61DS19 LHM BVH (son's); 71DS21 BVH; 73SM 3.0; 73SM EFI (Megasquirt); 73SM 3.0 (other son's)

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