Water Pump and AC Compressor Leak Symptoms

rt7085 · Yesterday, 05:20 PM

In 2022, I replaced my failed water pump on my 2008 E91 328xi wagon. The pump was an all aluminum Pierburg version. I also replaced ALL coolant system hoses (except the ones that go to the cabin heater core) and the thermostat. My 'touch a hose you replace a hose' rule on a car of this age.

A few weeks ago I started developing a new coolant leak. After a considerable amount spent with mirrors, borescopes and removing the reinforcement plate to get a good look I have observed 2 leaks in fact.

I *think* the water pump is leaking the blue coolant from the seam between the impeller housing and the e-motor section. See the picture below. Is this a common failure of these pumps? Note: It leaks when I pressurize the coolant system to approx. 20 psi. It is a fast dripping, about once every two seconds. It stops when the pressure is relieved. I think the seal has let go. And I made sure none of the hose connections is leaking by cleaning and pressurizing the system.

Name: pierburg_waterpump.jpg
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Name: pierburg_waterpump.jpg
Views: 27
Size: 400.4 KB

The second leak is from the AC compressor. I think it is leaking the refrigerant oil. It appears more green. See the picture below. It is very slowly dropping. Is this also a common failure for these compressors?

Name: mehle_ac_compressor.jpg
Views: 27
Size: 700.1 KB

Name: mehle_ac_compressor.jpg
Views: 27
Size: 700.1 KB

Thank you for your insights!

rt7085 · Today, 08:20 AM

What replacement shall I buy for the AC compressor: Nissin, Denso or BMW? And advice and experience?

mainbearing · Today, 01:42 PM

If you bought the pump from FCP then replace it under their lifetime policy. Was the AC compressor also from FCP? Then get a warranty claim. Neither of them should leak like that.

For AC compressor get a Denso. According to Rockauto's catalog it is the OE manufacturer for the vehicle. $345 on Rock. UAC and GPD are low cost aftermarket compressors if you want to try them. The GPD on Rock looks like a fave item along with Denso.

I am not sure if the desiccant bag is still removable on that model year, but change it if you can.

AC compressor:
https://www.rockauto.com/en/catalog/...ompressor,6628

Desiccant bag:
https://www.rockauto.com/en/catalog/...+element,16858

Just in case your leak may be caused by over-pressure from a plugged up condenser :
https://www.e90post.com/forums/showthread.php?t=2147099

Yesterday, 05:20 PM	#1
rt7085 Private 31 Rep 74 Posts Drives: E91 328xi / Merc GTS / RS6 Join Date: Mar 2016 Location: West Newton, MA iTrader: (0)	Water Pump and AC Compressor Leak Symptoms In 2022, I replaced my failed water pump on my 2008 E91 328xi wagon. The pump was an all aluminum Pierburg version. I also replaced ALL coolant system hoses (except the ones that go to the cabin heater core) and the thermostat. My 'touch a hose you replace a hose' rule on a car of this age. A few weeks ago I started developing a new coolant leak. After a considerable amount spent with mirrors, borescopes and removing the reinforcement plate to get a good look I have observed 2 leaks in fact. I think the water pump is leaking the blue coolant from the seam between the impeller housing and the e-motor section. See the picture below. Is this a common failure of these pumps? Note: It leaks when I pressurize the coolant system to approx. 20 psi. It is a fast dripping, about once every two seconds. It stops when the pressure is relieved. I think the seal has let go. And I made sure none of the hose connections is leaking by cleaning and pressurizing the system. The second leak is from the AC compressor. I think it is leaking the refrigerant oil. It appears more green. See the picture below. It is very slowly dropping. Is this also a common failure for these compressors? Thank you for your insights! Last edited by rt7085; Yesterday at 05:26 PM..
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Today, 08:20 AM	#2
rt7085 Private 31 Rep 74 Posts Drives: E91 328xi / Merc GTS / RS6 Join Date: Mar 2016 Location: West Newton, MA iTrader: (0)	What Brand AC Compressor What replacement shall I buy for the AC compressor: Nissin, Denso or BMW? And advice and experience?
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Today, 01:42 PM	#3
mainbearing Lieutenant Colonel 1126 Rep 1,733 Posts Drives: BMW 328i Join Date: Apr 2019 Location: LA iTrader: (0)	If you bought the pump from FCP then replace it under their lifetime policy. Was the AC compressor also from FCP? Then get a warranty claim. Neither of them should leak like that. For AC compressor get a Denso. According to Rockauto's catalog it is the OE manufacturer for the vehicle. $345 on Rock. UAC and GPD are low cost aftermarket compressors if you want to try them. The GPD on Rock looks like a fave item along with Denso. I am not sure if the desiccant bag is still removable on that model year, but change it if you can. AC compressor: https://www.rockauto.com/en/catalog/...ompressor,6628 Desiccant bag: https://www.rockauto.com/en/catalog/...+element,16858 Just in case your leak may be caused by over-pressure from a plugged up condenser : https://www.e90post.com/forums/showthread.php?t=2147099
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