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Thread: Mysterious Fluid Leak

  1. #1
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    Mysterious Fluid Leak

    My 97 M3 Sedan has been sitting in my family's garage since January as I've been waiting to bring it up to Michigan until the weather clears. I've been having my dad start the car a couple times a week and letting it run, but it hasn't been driven since I parked it. Today, my dad called and told me there's a sizable puddle of fluid underneath the car near the front of the engine, somewhere between where the water pump is mounted and the front of the radiator. I posted a link to a short video where my dad touches the fluid to show a bit of the fluid's properties. I can't for the life of me think of the fluid that would look and behave like this. My dad says It's almost crystal clear, with a slight green tint to it, and its very sticky and stringy when he touches it and pulls his finger off. Does anyone have any ideas?

    The only things I can think of are:
    1. Power steering rack leak
    2. Possibly coolant, allow me to elaborate: When I drove the car back from NC to Indiana, I stopped at a family member's house to show off the car and then discovered a pin hole leak in the upper radiator hose line that goes to the overflow tank (the one that rest in the top of the fan shroud). When I replaced the hose, I topped off the coolant that had been lost. There were no BMW dealers around and I had no idea what coolant was currently in the car when I bought it, other than that it was green. So I looked up what coolant it took on autozone and bought that (Prestone 50/50 https://shop.advanceautoparts.com/p/...2100/7020013-p). Is there any possibility that mixing the two types of coolant could've resulted in the creation of this strange substance now leaking out of the car?

    My dad's taking it to a local shop next week where they can put it up on a lift and try to identify the leak but in the meantime I thought I'd see if anyone had any ideas. I'd prefer to fix the problem myself, whatever it is, as that's one of the main reasons I bought the car, to learn more about cars and be able to work on them.

    https://imgur.com/gallery/Bw9f8JP

  2. #2
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    Ideally you should use the BMW coolant mixed 50/50 with distilled water as directed, but no mixing other types of coolant isn't going to cause any catastrophic issues like that. It just probably isn't ideal in the long-term.

    It looks more like coolant than dirty ATF from your PS system, but if you get under there you should be able to find the source. If it's the PS you'll almost certainly see signs of a leak coming from the bottom of the reservoir or one of the hoses coming out of it. If it's coolant it could potentially come from any of the numerous connections but popular places are the the expansion tank and its connections as well as the thermostat housing and the connections of the big hoses on either side of that. Look in the top of the engine bay for any sign of dried coolant around the expansion tank, radiator neck, or on the hoses you can see from above, and then do the same thing from underneath.

    For another data point, I recently fixed a small chronic coolant leak on my car which was coming from the connection between the lower radiator hose and the thermostat housing. The hose clamp was on unevenly and had worn away bits of the hose over time causing a small leak. I replaced the hose and clamp, and also the thermostat/housing and expansion tank while I was in there.
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  3. #3
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  4. #4
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    Quote Originally Posted by MauiM3Mania View Post
    Was the source of the leak discovered?
    A "quick" update:

    After my original post, my father placed some cardboard underneath the car to see if he could get a better idea of where the fluid was coming from. Since then it hasn't leaked a drop (go figure). He was planning on dropping it off at a shop last weekend, but we were graced with some warmer weather so he took it out for a drive and got it up to temperature. After driving it around a bit, he parked it over the cardboard and checked periodically throughout the day, reporting that he could see no leaks whatsoever. After doing some more research, I believe there are a few possibilities:
    1. The leak is incredibly slow, and the puddle of fluid found under the car has been accumulating since the car was last driven (approximately 1.5 months). I'm fairly confidant that the fluid is coolant that has evaporated, leaving behind a very sticky, concentrated substance. As to where the coolant is leaking from, I think that given the position, the most likely culprit is the metal thermostat housing that the previous owner installed. I've read that not only have others had problems with them sealing properly, but they also have known porosity defects, being die cast. IF the car is leaking, and IF it's coolant I believe this is the most likely scenario, which leads me to...
    2. The car is not leaking. When I replaced the upper return hose that goes to the expansion tank, I tried my best to clean any coolant off the engine and components that I could. I'm sure that I missed some, considering the leak sprayed directly into the clutch fan and slung coolant all over the engine bay. The fluid on the floor could be some residual fluid that has slowly dripped down from places I couldn't reach. Furthermore, my father has been starting the car a couple times a week and letting it run, and I'm sure he's left the climate control set to whatever I had it at when I drove the car back from NC. I'm guessing the A/C is kicking on periodically to regulate the temperature inside, which could possibly result in some condensation forming in the engine bay on the AC lines. If those lines have coolant on them from the leaky hose, then maybe the condensation and coolant mixed and dripped onto the floor over the past month or so. May seem a bit far-fetched, but I really can't think of any other answers.

    I'm hoping to be able to make the trip this weekend to work on the car a bit and will have the chance to get under it myself (finally bought a jack and some stands). If not this weekend, then definitely the next. I'll update again once I can look at things myself.

  5. #5
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    If you mix OAT type coolant (the orange/red stuff) with regular coolant, you will get some slimy brown stuff if I recall correctly. Honestly you don't need to use the BMW blue coolant, plenty of people have used regular stuff and have had no issues. Just make sure you do not mix incompatible coolants together.

  6. #6
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    Sorry for the delayed update for those following along. I was able to work on the car last weekend and ended up replacing the fan shroud after breaking a small portion off where the expansion tank attaches. Unfortunately, I learned the hard way that the easiest way to install the new part was to remove the radiator, marry the two pieces together, attach the lower radiator hose to the expansion tank and attach the expansion tank to the shroud. In the process, I got a good chance to examine all the radiator hoses at the front of the car. All of the hoses looked good and were still soft. I did find a spot at the bottom track of shroud where the radiator hose sits with a little sticky pool of evaporated coolant. There's a small hole on the underside of the "skid plate" that sits under the radiator, and it looks like the coolant that collected at the bottom of the fan shroud was slowly trickling onto the skid plate and then draining out the hole.
    I ended up having to drain the coolant system and after several drives and top-off's, was unable to find any leaks. I am assuming that the dried puddle of coolant at the bottom of the shroud was the residual coolant that I couldn't clean off of the engine bay after I replaced the upper radiator hose back in January.
    I'll be monitoring it when I bring it up to MI, hopefully in a few weeks, and my dad is checking it every couple of days as well.
    Thanks to all who offered ideas and advice!

  7. #7
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    For future reference the fan shroud can be somewhat easily removed once you remove the fan. You just need to undo a pin/clip at the top of each side and then you can at least move it around. It hooks onto a ledge on the radiator on each side to stay flush. If you want to take it completely off you need to disonnect the long hose that connects to the bottom of the expansion tank and feed it back out through the fan shroud as you pull it off.
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  8. #8
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    Quote Originally Posted by TostitoBandito View Post
    For future reference the fan shroud can be somewhat easily removed once you remove the fan. You just need to undo a pin/clip at the top of each side and then you can at least move it around. It hooks onto a ledge on the radiator on each side to stay flush. If you want to take it completely off you need to disonnect the long hose that connects to the bottom of the expansion tank and feed it back out through the fan shroud as you pull it off.
    Yeah, I found the clips and fed the hose through, but actually just ended up using some side-cuts to cut apart the old shroud and get it out. I realized that about halfway through that taking the fan out would've made things easier, but I was a little intimidated just taking the radiator off and making sure I put it all back together right; I didn't want to risk taking the fan off if I didn't have to and reinstalling it improperly. Now that I know how it all goes back together, I'll probably end up removing the clutch fan and installing an electric fan and new radiator later down the road. All part of learning a new vehicle!

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