504 radiator switch
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  1. #1
    Fellow Frogger!
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    Default 504 radiator switch

    I know this topic has been well covered but I have a 1974 504GL (automatic, no A/C), standard radiator with good flow, electrostatic fan that works. Typically runs 1/3 into the midrange (black) of the temp gauge except in highway traffic on a hot day when the temp will go up to, nearly into, the red zone. To give myself a little more headroom I obtained a crossflow radiator plus fan shroud from an '85 505GL to potentially replace my original 504 radiator (photos below, not the actual old radiator on left but same style). Also grabbed the electric AC cooling fan from the same vehicle. The options would be 1) replace the electrostatic fan with the electric fan and keep the original radiator (or maybe have 2 fans?) 2) replace the radiator and keep the original fan 3) replace both the radiator and fan. Here’s the question/issue. The new radiator has (according to the 505 owners manual) a very odd 12 lb screw cap vs the conventional 4lb cap on my old radiator (see below). Not sure if I can find a 4lb screw cap and am worried about pressurizing my system to 12 lbs. Also not convinced that the new radiator (tested to have no leaks and good flow) will improve my situation that much. Alternatively is there any chance my car would run cooler with a lower range temperature switch in my existing radiator (unknown range, unsure how to tell)? Any thoughts would be appreciated.

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    504 radiator switch-setup.jpeg504 radiator switch-old-rad.jpeg504 radiator switch-new-rad.jpeg504 radiator switch-fan.jpeg

  2. #2
    1000+ Posts BIGRR's Avatar
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    Radiator fan switch will be stamped on one of the nut flats (you may need to use a bit of emery on it).

    My 1973 Ti runs standard 504 radiator with 75C thermostat along with a 92C/82C radiator fan switch. No problems .

    Have no idea about attaching 4lb cap to 505 radiator, but you should only run 4lb in radiator of 504 (Sleeve seals might fail!)

    Qs:

    Are you sure the engine is timed correctly? (say 8 BTDC static).

    Are you sure the welch plug in the head behind the water pump impellor is in position?

    Good Luck
    Present fleet:-
    Peugeot 93' 205 Gti 16v
    Peugeot 73' 504 Ti from new
    Peugeot 08' 407 Hdi Coupe from new

    Previous fleet:-
    Peugeot 95' 605 Sv
    Peugeot 92' 205 Gti
    Renault 72' 16TS from new
    Renault 69' 10
    Renault 71' 10s
    Renault 68' 10 from new

    "Be reasonable do it my way!"


  3. #3
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    When you say good flow how did you test it?
    It sounds like the radiator tubes are partially blocked so the efficiency is reduced

  4. #4
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    As you know 504s are fine when the cooling is perfect but it doesn't take much to upset their little applecart, coolingwise. A bigger radiator will give the headroom and will be ok with the standard fan which unusually still functions perfectly. The electric fan could be triggered off the same sensor so both come on together but you will think that you have hit a brick wall powerwise! Or try the electric fan only after disconnecting the standard one. Neil

  5. #5
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    Hmm, very interesting. Pretty sure it's not a welch plug problem as I do not have antifreeze in the oil or vice versa. The timing is also set at 5BTDC but I can double check that. I will also check the stamp on the radiator fan switch. But yes, if there is anything amiss it is either the fan which works but maybe not perfectly? Or more likely the radiator which is a salvaged replacement for the original and was stated after some unknown test at the radiator shop to have OK flow (which in retrospect was maybe faint praise). I do think the 505 radiator might help even with the stock fan but I am really leary of subjecting my heater core and everything else to 12lbs of pressure. Really don't want to exchange an annoyance for a major problem. I have read on this site of others who run the crossflow 505 radiator in their 504.

  6. #6
    1000+ Posts jo proffi's Avatar
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    Apart from good tyres and an occasional oil change, the best investment you can make in an old car is a new radiator and some decent coolant.

    These days radiators are usualy rather cheap and the difference it makes compared to an old radiator is profound.

    There was a time when I stuffed around with old radiators and like your story, the car would always freak me out in slow uphill traffic.


    Jo

  7. #7
    1000+ Posts BIGRR's Avatar
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    Trial advancing timing to 10 BTDC.

    The welch plug spoken about is actually water both sides and is only able (to my knowledge) to be viewed by removing the water pump, see pic "x" marks the plug.
    Attached Thumbnails Attached Thumbnails 504 radiator switch-pump-chamber.jpg  
    Present fleet:-
    Peugeot 93' 205 Gti 16v
    Peugeot 73' 504 Ti from new
    Peugeot 08' 407 Hdi Coupe from new

    Previous fleet:-
    Peugeot 95' 605 Sv
    Peugeot 92' 205 Gti
    Renault 72' 16TS from new
    Renault 69' 10
    Renault 71' 10s
    Renault 68' 10 from new

    "Be reasonable do it my way!"


  8. #8
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    BIGRR, it looks like the plugless head.

  9. #9
    1000+ Posts Beano's Avatar
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    Why do you think this, 2pac ? His car is a 1974 model, which is pretty early ! Even my 1983 505 had a welsh plug behind the water pump, though my 1985 model was a plugless head.

    Mr Pieper, the plug in question is as RR says : water on both sides.
    When the welsh plug (behind water pump) has eroded away, the car overheats after some time (not quickly), as it affects the way water flows through the head. It seems to me that this may well be the problem, as you say it happens on the highway.

    I have always maintained that the integrity of this plug needs to be a known quantity....because sometimes it comes out and flips to one side, locking up the water pump. This then causes the fan belt to break, and the car will need to be towed home.
    There are descriptions elsewhere of how to replace it by screwing in a circular brass or aluminium piece (using stainless steel screws ONLY, as they are very very strong).

    Don't....whatever you do....ever pressurize your cooling system to 12 lbs. I have run completely UNpressurized systems in 504s and 505s for years. (But then also, I do not use air-conditioning).
    I have seen too many good engines ruined by a hose blowing, and people not noticing the overheating till too late. Even if you do it temporarily, it is better than pressurizing to 12 lbs. As someone else said....you risk blowing the seals at the bottom of the cylinders....between water and oil.
    Last edited by Beano; 24th August 2014 at 02:27 PM.

  10. #10
    1000+ Posts BIGRR's Avatar
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    Quote Originally Posted by 2pac View Post
    BIGRR, it looks like the plugless head.
    Blow the photo up you will see the (rusty steel) plug! See pic below of one repaired about 1990!

    I have wired a (spare) warning light in the dash in parallel with the radiator switch on my car. I also can switch on the fan if for any reason the motor got hot (I used to tow a trailer and car in Sunday afternoon city traffic) usually at the bottom of hills so fan did not cut in up the hill (more power for the hill).
    Attached Thumbnails Attached Thumbnails 504 radiator switch-dsc01083.jpg  
    Last edited by BIGRR; 23rd August 2014 at 11:50 PM.
    Present fleet:-
    Peugeot 93' 205 Gti 16v
    Peugeot 73' 504 Ti from new
    Peugeot 08' 407 Hdi Coupe from new

    Previous fleet:-
    Peugeot 95' 605 Sv
    Peugeot 92' 205 Gti
    Renault 72' 16TS from new
    Renault 69' 10
    Renault 71' 10s
    Renault 68' 10 from new

    "Be reasonable do it my way!"


  11. #11
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    Quote Originally Posted by Beano View Post

    Don't....whatever you do....ever pressurize your cooling system to 12 lbs. I have run completely UNpressurized systems in 504s and 505s for years. (But then also, I do not use air-conditioning).
    I have seen too many good engines ruined by a hose blowing, and people not noticing the overheating till too late. Even if you do it temporarily, it is better than pressurizing to 12 lbs. As someone else said....you risk blowing the seals at the bottom of the cylinders....between water and oil.
    beano, what do you mean by pressurized and unpressurized cooling systems?

    anyway, according to 505 haynes the pressure cap is either 0.8 or 1 bar.
    Last edited by 2pac; 24th August 2014 at 02:54 AM.

  12. #12
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    OK, some updates. Car is at 5 degrees BTDC and runs pretty well. Hoses and tranny fluid level good. Welsh plug, crimony I just replaced the water pump maybe 4 months ago and although i didnt specifically check i didnt notice anything unusual in the Welsh plug area and the old pump certainly didnt have any impellers bent or broken off. It was a pain to remove the pump so I'm sorry beano, for now the integrity of the plug will have to remain an unknown entity. Radiator fan switch was new maybe a year ago, 68-82 degree range. I pulled it out and when dipped in hot water i did hear a click. However when testing with an ohmmeter there was a lack of continuity even in hot water i.e. no electrical connection, no fan engagement. This is puzzling because I have seen the fan run and heard it clunk on although perhaps this is only being triggered sporadically. I would have thought these switches were more solidly built. Anyway picking up new one tomorrow, same range. If this doesnt help I'll check the welsh plug (argh) and after that it will be the radiator. Agreed with the concerns about 12lbs of pressure but the 505GL that donated the radiator with the 12lb cap had an XN1 engine just like my 504. Did Peugeot modify the XN1 and/or the heater core in the 505 to accommodate higher pressure?

  13. #13
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    Noone has mentioned that the 505 radiator has the external expansion bottle where the 12lb cap is. I have this set up in 2 504s currently running and I have not even had the temperature climb above half way whether towing a tonne of gravel up a hill or inland Australia.
    On both cars I have fitted an aftermarket wet bulb fan switch into the top radiator hose as well as the original radiator switch as a backup.
    Now, with the plastic radiator cap on the expansion bottle, there are two little plastic covers hiding 2 little valves....one for pressure release and I think one for allowing air back in I think during cooling.
    What I did was to cut these little springs to make them a lot softer to halve the pressure in the system. It is a bit of guesswork but I have had no problems with head gaskets or cooling systems.
    Good luck Bob

  14. #14
    1000+ Posts Beano's Avatar
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    Quote Originally Posted by rpieper View Post
    Did Peugeot modify the XN1 and/or the heater core in the 505 to accommodate higher pressure?
    Yes....but I can't remember what my mechanic friend told me was upgraded. But he was very emphatic about only using a 4 lb cap. As others have been too.


    Quote Originally Posted by 2pac View Post
    beano, what do you mean by pressurized and unpressurized cooling systems?
    Well, I guess you know what a pressurized system is....the 4lb cap, the 12lb cap etc. This is so that the engine can run hotter (more efficiently) without boiling off the coolant.

    Unpressurized means that you have a cap which simply blanks off the radiator cap hole. There is no spring or rubber bit inside. Then from the overflow, a hose runs to an overflow tank. Coolant can run to and from this tank as necessary. It's atmospheric pressure only. There is much less chance of a hose blowing and causing you to lose all your coolant (and not noticing till too late) because there is no pressure in the system. Renault 12s had this standard.
    You don't really need a pressurized system unless it runs hot like modern cars. If you have air con, it will cause the car to run hot. But no air con = no need for pressurization.
    I just check the coolant level regularly. Oh...and I run a 504 thermostat in my 505 (slightly cooler)
    Last edited by Beano; 24th August 2014 at 02:25 PM.

  15. #15
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    the pressure cap is on the radiator or on the expansion bottle or both?

    what i had in my previous radiator is a cap of this sort, and a tube running from the orifice down to the road.
    504 radiator switch-p1030787.jpg

  16. #16
    1000+ Posts BIGRR's Avatar
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    Seeping head gasket?

    Before removing water pump.
    Compression blowing into cooling water under load? Any bubbles in radiator water:- remove cap, warm up motor, have someone put load on engine, drive against hand brake, look for bubbles?


    There are tests that can analyse if there is CO2 in your cooling system water.

    Just more thoughts.
    Present fleet:-
    Peugeot 93' 205 Gti 16v
    Peugeot 73' 504 Ti from new
    Peugeot 08' 407 Hdi Coupe from new

    Previous fleet:-
    Peugeot 95' 605 Sv
    Peugeot 92' 205 Gti
    Renault 72' 16TS from new
    Renault 69' 10
    Renault 71' 10s
    Renault 68' 10 from new

    "Be reasonable do it my way!"


  17. #17
    1000+ Posts Beano's Avatar
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    And they're very good thoughts, BIGRR. In fact this happened to my 505 not too long ago. I had thought the radiator was clogged. I can't remember what caused me to finally suspect the gasket. There were no bubbles coming up into the water. I drove it like that for months, and when I took off the head, was amazed that the gasket had not actually blown. But I could see where the gases had been blowing/seeping across. Usually gaskets blow (completely) fairly rapidly after this kind of thing, but not mine.
    And the symptoms were the same. Sorry I had not thought of this earlier.

    Mr R Peiper : I suggest that you go to a garage and get a tiny sample of your coolant tested. They do it in a small bottle with reagent added to your coolant.....similar to those swimming pool water testers.
    Oh...and they test for CO (carbon monoxide) in the coolant. Not CO2
    Last edited by Beano; 24th August 2014 at 06:03 PM.

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