Coolant leak--can't track it down

[usinjin]

I know this has been asked about a thousand times--I have a coolant leak, and I can't figure out where it's coming from. I'm trying to figure out if there's a place that poses a higher failure rate than others. I'm not sure I can afford a complete cooling system overhaul at the moment, though I probably need one. Car has 144k miles.

Anyways, here's what happens--Coolant will leak out over the course of about 2 days of driving, but it will only fall to a certain level. At this level, the car runs fine and the temp needle remains centered. The only indication I get is the low coolant light cycles on and off. It'll be on for about 5 mins, then off for 30. Something like that. If I take the cap off the expansion tank, it's dry. I fill to the proper level, bleed the system, and it's good for 2 more days.

I cannot for the life of me find where the leak is coming from. Under the car looking up, and looking under the hood, I can see nothing.

The car has a new OEM lower radiator hose, and a slightly dubious used radiator from a Ci. (rolls eyes) I've replaced the expansion tank like 3 times over the 3 years I've had it.

My question is, after the expansion tank, is there another likely failure spot that I could start with replacing?

[sillieidiot]

Pretty much everything along the cooling system is suspect lol Usually it's the tank, upper/lower hoses, water pump, and radiator. I guess you could start with the hoses since those are the cheapest.

[usinjin]

Pretty much everything along the cooling system is suspect lol Usually it's the tank, upper/lower hoses, water pump, and radiator. I guess you could start with the hoses since those are the cheapest.

Rats. Is there some sort of safe dye I could put in the coolant to try and make the leak more apparent? Gently pump air in and listen for hissing?

The water pump has never been replaced. I replaced the radiator about 10k back with a beautiful new one, and my then-mechanic broke the fan shrowd and destroyed the radiator, so he replaced it with a used one. So it could be the radiator. RIP car

[Vas]

The o-ring on the temp sensor that sits in the lower radiator hose is prone to leaking. Also the water pump can leak but you won't be able to see it unless you remove it.


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[sillieidiot]

Rats. Is there some sort of safe dye I could put in the coolant to try and make the leak more apparent? Gently pump air in and listen for hissing?

The water pump has never been replaced. I replaced the radiator about 10k back with a beautiful new one, and my then-mechanic broke the fan shrowd and destroyed the radiator, so he replaced it with a used one. So it could be the radiator. RIP carThe coolant itself is already colored. Probably best that you try to really clean all the areas down then look to see if you can find the leak. You'll see either the coolant or if dry, it'll be white flakes. I would definitely replace the water pump if it's never been replaced. This things don't last long at all.

I think you'll have to look for dry residue of the coolant. It sounds like the coolant is evaporating somewhere.

[usinjin]

Sounds like the pump is a good place to start. The coolant sensor and o ring is actually also fairly new forgot to mention.

[Oli77]

Are there not coolant lines that go under the intake to feed into the interior radiator (for cabin heating)? Could those be leaking as well?

I think you could see if there was a leak at the water pump.

[BMWM3186]

I have to top mine off every month or 2. Everything looks clean and dry... very frustrating. Cooling system was changed 40k ago.

[3ZHP]

Pull your belt and pulley to check your water pump weep hole. You may want to rent or borrow a pressure tester while doing the inspection

https://youtu.be/9476cw9ByRk

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[Fried_Chicken]

Spray the entire engine with water; let it dry, then drive it like you stole it. Look inside the engine after and find out where the blue cruddy shit is.

[JohnnyGraphic]

Don’t forget to check under the thermostat housing.

There are other hoses that go on the drivers side back to the firewall. But it’s under the intake etc. those don’t leak as often. The areas that are prone to leaks and FAILURES are the ones already mentioned. I wouldn’t drive too much without getting it fixed. Youve got a ticking time bomb.

You’d see the bluish white residue wherever there is a leak.

[usinjin]

Thanks for all the great suggestions. I am doing my best to find it, as at this point it now leaks fast enough that if I drive it briskly enough it will lose the coolant in the first 20 mins of driving or so. Will report back findings!

[Fried_Chicken]

Thanks for all the great suggestions. I am doing my best to find it, as at this point it now leaks fast enough that if I drive it briskly enough it will lose the coolant in the first 20 mins of driving or so. Will report back findings!

You will definitely find blue cruddy shit wherever the leak is.

[JohnnyGraphic]

Thanks for all the great suggestions. I am doing my best to find it, as at this point it now leaks fast enough that if I drive it briskly enough it will lose the coolant in the first 20 mins of driving or so. Will report back findings!

What coolant are you using? If you’re using BMW coolant, then you should see the blue/white residue. If it’s aftermarket, then that changes things.

Let us know so we aren’t sending you on a wild goose chase.

[usinjin]

What coolant are you using? If you’re using BMW coolant, then you should see the blue/white residue. If it’s aftermarket, then that changes things.

Let us know so we aren’t sending you on a wild goose chase.

BMW coolant. So far I'm only seeing flecks appear around the expansion tank (near the top rim). Again, tank isn't that old, and nor is the cap.

School has got me busy but when I get time I'd like to replace the water pump regardless of if the seal is leaking. 145k miles and it's the original.

Yesterday I noticed some fluid pooling under the car near the middle, but I had to leave and couldn't see if it was coolant or not.

[SureShot434]

BMW coolant. So far I'm only seeing flecks appear around the expansion tank (near the top rim). Again, tank isn't that old, and nor is the cap.

School has got me busy but when I get time I'd like to replace the water pump regardless of if the seal is leaking. 145k miles and it's the original.

Yesterday I noticed some fluid pooling under the car near the middle, but I had to leave and couldn't see if it was coolant or not.

There are two pipes that run under the intake that are prone to cracking. I just rebuilt my motor and when I removed them parts of the ends actually broke off in the head and back of the timing chain cover. One of the pipes goes from your head to your heater core valve via a rubber hose, and the other goes from the back of the water pump to the expansion tank. These pipes should be replaced by 100k miles. You have to removed the intake to replace these coolant pipes but it is well worth it. While you are at it you could replace your heater core hoses, and the CCV.

These are the two pipes.
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