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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Tue, Apr-23-2019, 02:11:11 PM   #1
zl
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Default Coolant Leak From Rear Passenger Side

Long story short, I have a leak that is coming from the rear passenger side of my engine block. At this point, I feel like it can be one of two things--either the coolant hose that goes from the heater core to the back of the engine block, or the head gasket. There is coolant ALL over the upper oxygen sensor and below that on the exhaust manifold that I found when going to drain the engine block of coolant. Here is a picture (for reference, the drain plug for the engine is behind the oxygen sensor at the top of the picture, and it is taken looking directly up):

https://i.imgur.com/KctJc7K.jpg

My next plan is to remove the intake manifold since I can't for the life of me see what is going on back there. If its the hose, I should be able to replace it at that point, and if it is the head gasket... well... remove the intake manifold is the next step anyways. Am I on the right track here? I'm not sure if the heater core could crack and cause what I'm seeing as well.

Right now I have the coolant system removed from the car and I'm going to replace most components/hoses (radiator, tank, gaskets etc). I started this project because of a slow coolant loss issue I've been having that seems to have been getting worse, and there was definitely a small leak coming from the thermostat housing. I found pitting on the cylinder head where the gasket is supposed to seal, so I went ahead and put some JB weld in there and sanded it down (still not done sanding though). Pics of that:


https://i.imgur.com/KctJc7K.jpg

https://i.imgur.com/NQWsAaj.jpg

Last edited by zl; Tue, Apr-23-2019 at 03:50:55 PM. Reason: picture size
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Old Tue, Apr-23-2019, 03:21:16 PM   #2
Texaz3
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Default Re: Coolant Leak From Rear Passenger Side

Do you have coolant mixing with the oil? Check the inside of the oil cap for white "mayo" like substance. That would confirm head gasket failure. If not - then likely the hose.
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Old Tue, Apr-23-2019, 03:30:10 PM   #3
JitteryJoe
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Default Re: Coolant Leak From Rear Passenger Side

If the heater core then you should see/smell coolant inside the cabin especially with the heater on. It tends to fog up the windshield with defroster on.
Changing the heater core is a PITA so hopefully not that and just a bad hose.
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Old Tue, Apr-23-2019, 03:43:03 PM   #4
zl
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Default Re: Coolant Leak From Rear Passenger Side

Great questions, forgot to add some extra information:

The oil is not milky at all. There is no junk when I take the oil cap off.
I don't notice any coolant smell inside the cabin, nor does the windshield fog up.
There is no white smoke coming out of the exhaust.

So, I'm assuming if there is a failure in the head gasket right now, it is simply a leak from the coolant channel to outside of the block. Either way, I think today I'm going to remove the intake manifold.

Edit: Also, here is another post of someone who had the leak I'm describing: https://www.bimmerforums.com/forum/s...1#post23860971
Hopefully I can get a better look at it--its in such a terrible spot.

Edit 2: Went in and removed some more things to get a better look. I dropped some water on top of the hose connection at the back of the head and the water seemed to fall in the general area I found coolant before, so I think I'm going to just replace that hose and see what happens.

And a picture of the car!

https://i.imgur.com/Et13UY7.jpg

Last edited by zl; Tue, Apr-23-2019 at 10:11:45 PM.
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Old Sun, May-12-2019, 09:23:53 PM   #5
zl
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Default Re: Coolant Leak From Rear Passenger Side

So, for an update:

I replaced the hose that connects on the rear of the engine block. The hose looked like it was in good condition.

I filled with all distilled water and a UV dye, bled the system (that was a huge pain after draining the block too!), and took it for a few short drives to make sure it was completely full. Didn't see any leaks after several heat cycles and a full system, so I took it for an hour+ long spirited drive on some twisty back roads, making sure to really put some heat into the engine. I immediately jacked the car up and took a look with the UV light--no leaks!! I drained the radiator, and put about a gallon of straight coolant back in to have the right mix.

Long story short, I think the leak came from the pitting where the thermostat housing couples with the cylinder head. The dried coolant on the exhaust probably came from the leak traveling backwards from wind? I'm not sure. Either way, the problem seems to be fixed!
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Discussing Coolant Leak From Rear Passenger Side in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)