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Discussion Starter · #1 ·
Hey everyone, need some help; i know coolant leaks are common on on E39's, done a lot of reading here and i'm still coming up empty. I have 2002 540i M sport 6 gear, 154000 kms (95 miles); car has been going down on a coolant, not a huge amount, about a cup every two weeks. Pressure tested system, found a crack in the rad; replaced rad and tank. Started driving the car again, still going down on coolant. Pressure tested system, didn't drop any at 15 psi for an hour. No external leaks, nothing on the driveway. Put dye in the system, drove the car for a day, looked high and low, nothing. Should I be suspecting a poss head gasket? No smoke, car runs like a champ with good power,no codes, not overheating....completely stumped. Suggestions???
 

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Before I'd suspect a head gasket leak (not very common), I'd check out the valley pan for a leak. They tend to leak (in a USA car) on the right/passenger side, towards the back of the engine (closest to the firewall).
What happens is coolant leaks out slowly, and evaporates before you'd see an drip out.
If you can straighten out a coat hanger & slide it down in that corner, you'd see coolant on it if the valley pan is leaking there. It's kinda an awkward area to get to see back in there.
 

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Discussion Starter · #3 ·
Thank you for the quick reply.I've been suspicious of the VP gasket, but wouldn't I still lose pressure from the test? Or does the VP start to leak once the car is screaming hot?
 

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The valley pan would leak when cold when you did a pressure test if it was bad.
Sure you got all the air out when you replaced the radiator and expansion tank?
It's common for the level to drop some for a few days after you replace parts. How much coolant have you had to add?
 

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Discussion Starter · #5 ·
I have gone through close to 4 litres in a month and a half. I agree about the level dropping after I did the work, that's why I didn't panic at first. I haven't suspected it being air locked as the car makes good heat, gauge doesn't fluctuate, no gurgling sounds, etc. Safe to say I'm baffled...

On a different subject, what are you running on your for shocks and springs? Really like the look of your ride height!
 

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If you have good heat then you don't have an air pocket.
4.5L is a lot of coolant. Sure you don't see any leaks or steam coming out of the exhaust?
Can you connect the pressure tester and then start the engine to warm it up, then pump it up to ~15 PSI to check it hot?

I dropped the car using H&R 50464 springs. I also have Koni FSD's but they don't have anything to do with dropping the ride height.
I later raised the front 1/2" using spacers so I wouldn't scrape going over speed bumps.
This pic is without the spacers.
 

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Discussion Starter · #7 ·
No leaks that I can see, no drops on the driveway. Put dye in the system, drove the car for a day then went over it with a black light, couldn't find anything other than old residue from when I replaced the rad and reservoir. No smoke/steam from the tailpipe, doesn't run rough, starts good when cold...only other thing I can throw out there is there is a light smell from under the car after it's screaming hot; front of the cats are getting hit with something, but I just had the car undercoated as it's going into storage soon.

Are the 50464 on all 4 corners or just the front?
 

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Can you check the coolant for signs of hydrocarbon? That would tell you if it was a head gasket or cracked head.

Yes, all 4 corners. The H&R's were advertised to drop the front 3/4", however it was actually 1.5".
That's why I raised it up 1/2".
 

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Good idea, I'll give it a try.

Did you stick with the stock tire size when you dropped the ride height?
My experience with the H&R springs is the same; it could use another 1/2" of height to make it perfect.
 

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When I still had my car my coolant manifolds would leak on the back of the block. Both behind the valley pan and inside the bell housing.
Yes, that is another possibility, and the OP may want to put the car on a lift and check from below with a flashlight. If the cover inside the bell housing is leaking, there should be traces of coolant leaking out the bottom of the bell housing. The crossover pipe above the bell housing might also have coolant traces if leaking
 

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Before I'd suspect a head gasket leak (not very common), I'd check out the valley pan for a leak. They tend to leak (in a USA car) on the right/passenger side, towards the back of the engine (closest to the firewall).
What happens is coolant leaks out slowly, and evaporates before you'd see an drip out.
If you can straighten out a coat hanger & slide it down in that corner, you'd see coolant on it if the valley pan is leaking there. It's kinda an awkward area to get to see back in there.
My money is on the VP. I had the same problem. Did a cooling system overhaul and was still losing about a cup every two weeks. Finally I said F it!!! Has to be done at the mileage anyway. Problem was solved. Hope this helps
 

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Discussion Starter · #16 ·
Yeah, I'm starting think valley pan too... took the car to well known cooling specialist where I live and they came up with nothing also; they pressure tested to system to 15 psi both hot and cold, didn't drop at all. They rechecked for leaks with a black light as I had put dye in the system, zero...Had them bleed the system again for my own peace of mind. This is going to drive me to drink!
 

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Yeah, I'm starting think valley pan too... took the car to well known cooling specialist where I live and they came up with nothing also; they pressure tested to system to 15 psi both hot and cold, didn't drop at all. They rechecked for leaks with a black light as I had put dye in the system, zero...Had them bleed the system again for my own peace of mind. This is going to drive me to drink!
VP for sure bud. Thank us later:D
 
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