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M30 Guys: Coolant expansion tank details needed

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    #16
    Originally posted by CorvallisBMW View Post
    So here's my thinking on this: It's not that the air is going down through anywhere, it's that the coolant is pushing up. If there's 1.5" of fluid in the thermostat above the fluid in the expansion tank, that fluid is going to exert a downward force (called head pressure). It will push, albeit with a fairly small force, through the coolant passages of the engine and in to the expansion tank until the levels equalize. Meanwhile the air that's trapped in the expansion tank is going to push backwards through the vent line and in to the top of the radiator (this is what's different between my system and your bike; your reservoir is sealed, so the air cannot go anywhere. In mine, that vent line allows the air to move, which in turn allows the fluid to move. It's a straw with a finger only partially covering the top. If you drilled a tiny hole in your reservoir cap, the fluid would backflow down the line. Maybe I need to cap off my vent line???). Now with the engine off all of the pressures are equalized and the only force acting on the system is gravity. As such the fluid level is going to try and equalize itself everywhere in the system. Therefore the only way to keep air out of the engine is to ensure the fluid level in the expansion tank is at least as high as that point or higher.

    I understand that description. Does the vent line from the radiator really dump into the air of the coolant reservoir?

    A reservoir that dumped the rad vent below the coolant level would also solve that issue.

    Capping the line might be good idea to try to see if that is what is happening.
    Lorin


    Originally posted by slammin.e28
    The M30 is God's engine.

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      #17
      Originally posted by LJ851 View Post
      I understand that description. Does the vent line from the radiator really dump into the air of the coolant reservoir?

      A reservoir that dumped the rad vent below the coolant level would also solve that issue.

      Capping the line might be good idea to try to see if that is what is happening.
      The line actually seems to split. There is a small weep hole that bleeds above the coolant level. With the engine running and the cap off you can clearly see coolant coming out of it. But there's also a tube that goes down below the coolant level. If I blow air through the line, I can both hear it going through the weep hole and create bubbles from the bottom of the tube. It's quite odd.

      Maybe that weep hole isn't supposed to be there? Anyone else with the same expansion tank able to confirm by running there engine with the cap off and seeing if coolant sprays in from a small hole in the neck?

      edit: you can kind of see it here:
      Capture2 by Darin Schnoor, on Flickr

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        #18
        I don't have a late model expansion tank anymore, but that weep hole is present on quite a few other BMW models- it's how they "self bleed".
        1989 Zinnoberrot M3 Build Thread
        1990 Brilliantrot 325iS Build Thread

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          #19
          that's where the air from the radiator comes out.

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            #20
            Originally posted by AWDBOB View Post
            I don't have a late model expansion tank anymore, but that weep hole is present on quite a few other BMW models- it's how they "self bleed".
            Originally posted by LowR3V'in View Post
            that's where the air from the radiator comes out.
            Ya, but there's also a black plastic tube that goes down below the cold coolant level. If you remove the vent line at the radiator and blow in to it, bubbles come out from that tube. It's just odd that there's two ports for that vent line; one above the coolant level and one below.

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              #21
              Got a new tank cap, replaced the vent line with all new hose (just in case) and managed to raise the tank by fabbing some basic sheetmetal brackets. I can now fill the tank to the cold fill level with the bleeder screw cracked and fluid just barely starts to dribble out. So that's amazing, because now it means my fill level is above the highest point of the engine. Fingers crossed...

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                #22
                I got my fingers crossed for you as well.
                Lorin


                Originally posted by slammin.e28
                The M30 is God's engine.

                Comment


                  #23
                  I am using the stock b34 tank that attaches to the firewall, I also lowered the radiator more since it is an e36 M3 rad and has a shorter profile than the e34. I crank the heat and park with my car flat or slightly nose down to nudge air towards the higher tank. Crack the housing bleeder and that's all it ever takes for me. My issue right now is needing another fan for really hot days when the 16" spal won't cut it.

                  I plan to redo everything when I drop the engine out for a refresh while it's getting boost added. I can say it's at a shop now since not many look here in the m30 section.
                  ~ Puch Cafe. ~ Do business? feedback ~ Check out my leather company ~

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                  Current cars:
                  ~ '87 325 M30B35 swap
                  ~ '87 535
                  ~ 01 540 Msport 6spd
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                    #24
                    Originally posted by F34R View Post
                    I am using the stock b34 tank that attaches to the firewall, I also lowered the radiator more since it is an e36 M3 rad and has a shorter profile than the e34. I crank the heat and park with my car flat or slightly nose down to nudge air towards the higher tank. Crack the housing bleeder and that's all it ever takes for me. My issue right now is needing another fan for really hot days when the 16" spal won't cut it.

                    I plan to redo everything when I drop the engine out for a refresh while it's getting boost added. I can say it's at a shop now since not many look here in the m30 section.
                    How do you have your 16" pusher mounted? Is it directly on the radiator or spaced out a bit? I found that mine was spaced out around 1/2" and a lot of the air was just hitting the radiator and bouncing off instead of going through. Spal makes fan gaskets though, installing one of those made a HUGE difference.

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                      #25
                      i got one of those too.

                      i was thinking of even making like a tube with thin abs that goes around the fan to the grill so it gets air from the outside.
                      might help maybe not but in traffic my shit overheats in the summer.

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                        #26
                        Seems odd that your car overheats. How high are the ambient temps were you are? Is it humid? Are you running AC?

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                          #27
                          Originally posted by CorvallisBMW View Post
                          How do you have your 16" pusher mounted? Is it directly on the radiator or spaced out a bit? I found that mine was spaced out around 1/2" and a lot of the air was just hitting the radiator and bouncing off instead of going through. Spal makes fan gaskets though, installing one of those made a HUGE difference.
                          I need to get a fan gasket and see how that improves that cooling. Right now it is flush to the radiator and hard mounted to the core support with brackets and a foam between the fan and radiator. I wanted to get a smaller puller fan(10") then mount it inside the bay offset to the bottom passenger side.
                          ~ Puch Cafe. ~ Do business? feedback ~ Check out my leather company ~

                          Instagram: @BWeissLeather

                          Current cars:
                          ~ '87 325 M30B35 swap
                          ~ '87 535
                          ~ 01 540 Msport 6spd
                          ~ '06 X5 4.8is

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                            #28
                            i have the thinnest pusher 16'' spal makes.
                            once it gets to like 20mph it'll drop. not a cooling issue just
                            the fan is a baby. usually when it gets into the 90s.

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                              #29
                              Originally posted by F34R View Post
                              I need to get a fan gasket and see how that improves that cooling. Right now it is flush to the radiator and hard mounted to the core support with brackets and a foam between the fan and radiator. I wanted to get a smaller puller fan(10") then mount it inside the bay offset to the bottom passenger side.
                              Originally posted by LowR3V'in View Post
                              i have the thinnest pusher 16'' spal makes.
                              once it gets to like 20mph it'll drop. not a cooling issue just
                              the fan is a baby. usually when it gets into the 90s.
                              You can fit a 10" puller in front of the alternator, or probably something larger down by the AC compressor if you've removed AC.

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                                #30
                                ya maybe.
                                just shift the pusher to passenger side and put the puller all the way to the driver.

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