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BMW Cooling System Leak Test
 
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Pelican Technical Article:

BMW Cooling System Leak Test

Nick Czerula

Time:

1.5 hours

Tab:

$50

Talent:

**

Tools:

Cooling system pressure tester, flathead screwdriver

Applicable Models:

BMW E90 3-Series (2006-11)
BMW E91 3-Series (2006-12)
BMW E92 3-Series (2007-13)
BMW E93 3-Series (2007-13)

Parts Required:

Parts will be determined once leak is found.

Hot Tip:

Check for leaks with engine warm and cold.

Performance Gain:

Repair coolant leaks

Complementary Modification:

Replace associated hoses and cooling system seals.

Pressure testing your BMW cooling system is the best way to find leaks. However, not everyone has a pressure tester. I would suggest owning one if you plan to maintain your own vehicles, it can save quite a bit of time when locating a cooling system leak. You can also check for leaks without a pressure tester, but results are less accurate and the procedure is time consuming. I will cover pressure testing in this tech article, as well as some tips on checking for leaks without using one. Always start with a cool engine, if you do not find the leak, warm the engine with the pressure tester installed. At times, leaks will surface as parts expand from engine heat.

A cooling system pressure tester is used to pressurize a cooling system and hold at a specified pressure while looking for leaks. Coolant leaks can be internal (ie: head gasket) or external (ie: radiator), it is important to take these things into consideration when looking for a coolant leak. If you are losing coolant, but not seeing any on the ground, this would likely be an internal coolant leak. Puddles of coolant found under your vehicle would be from an external leak. Remember to properly clean any coolant that gets on ground and properly dispose of it. Place a drain pan under suspected areas of leaks to minimize coolant spills.

When pressure testing a cooling system, be sure the vehicle is cool and lacks pressure before removing the coolant expansion tank cap.
Figure 1

When pressure testing a cooling system, be sure the vehicle is cool and lacks pressure before removing the coolant expansion tank cap. (green arrow)

Once the cap is removed, install pressure tester adapter to the coolant expansion tank.
Figure 2

Once the cap is removed, install pressure tester adapter to the coolant expansion tank.

Pressurize system to 1.
Figure 3

Pressurize system to 1.5 bar (21.8 psi). Pressure should not drop more than 10% over a two minute time period. If pressure drops right off, that is a sign of a leak. Look for coolant on the ground. If no coolant reaches ground, you could have an internal leak. If you suspect head gasket leak, you need to test cylinder sealing via a leak down test. If coolant leaks externally, use a flashlight and follow coolant to source. Coolant leaking down the right side of engine could be water pump or thermostat. These are the two most common areas. From the bottom of engine, coolant will leak down from the cluster of cooling system components. Coolant leaking down the left side of engine can be from coolant hoses or from the oil filter stand / housing. Coolant leaking down radiator could be from radiator or a radiator hose. Inspect the side tanks on the radiator for signs of leaks or fresh coolant. Use a mirror to inspect the bottom of hoses and connections at the radiator.

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Comments and Suggestions:
William Comments: My 2008 E90 has a coolant leak. I took it to the BMW dealership and they said that it was the radiator that was leaking. I had the radiator replaced but it is still leaking but I can't find the leak. What could be the problem?
November 29, 2016
  Followup from the Pelican Staff: It could be anything in the cooling system from a hose to the engine. I would pressure test the cooling system and inspect the engine and cooling system for leaks. - Nick at Pelican Parts  
Ndo Comments: Is der a way of running a pressure test at home without having the actual pressure test tools, like a home made pressure test?
November 4, 2016
  Followup from the Pelican Staff: Not that I know of. - Nick at Pelican Parts  
Ndo Comments: Thanx a lot, il hav it pressure tested.
November 4, 2016
  Followup from the Pelican Staff: No problem. - Nick at Pelican Parts  
ndo Comments: Is der any damage dat might happen if I dont pressure test, but just keep on adding coolant every time that light pops up?
November 4, 2016
  Followup from the Pelican Staff: Yes. You could over-heat, damage the catalysts or engine, etc. - Nick at Pelican Parts  
moapys Comments: Hi Nick 'not a good week for my Bimmers; the '06/E90 decided to show low coolant, yet no sign of leakage. Refilled...two days later, low - maybe half quart - again. Did pressure test on system, held 20psi for 5+ mins. My experience looks like Brians same car, below. Guess I try cylinder leak down test next...?
October 31, 2016
  Followup from the Pelican Staff: No reason to suspect the cylinder head if it isn;'t smoking.

- Nick at Pelican Parts When the system is under pressure, wiggle hoses and connections. You may have a leaking o-ring or hose.
 
Ndoh Comments: E90, 2006, 330i. I noticed water coming out of the engine and the coolant light came on l. This was aftrr iv topped up water abt 3 days ago. Also I just made a service on da car abt 3000km ago and it wanted to b topped up with a litre of oil. Wat cud b da issue here?
October 29, 2016
  Followup from the Pelican Staff: Sounds like a leak, I would pressure test the cooling system. - Nick at Pelican Parts  
sam Comments: Hi Nick thanx for the response, the car is building pressure without even starting, the other night i left the cap open in the morning the water raised right till the top almost overflowing, when check water when its cold it releases what ever pressure it has if i check watef after 2 hrs there is pressure again
October 27, 2016
  Followup from the Pelican Staff: I can't imagine how that is possible. Unless there is a oil mix issue and other fluids are coming into the cooling system. Even then, when the engine is off, nothing should be moving around to build pressure. - Nick at Pelican Parts  
SAM Comments: BMW E90 330CHANGE WATERPUMP & THERMOSTAT ON 20/10/2016,OPEN THE WATER BOTTLE ON FRIDAY IT HAD PRESSUR IN IT SO IT THREW THE WATER OUT,CHECK ON SAT SAME THING-DROVE TO DBN AND BACK 1000K NO ISSUE CHECK WATER THIS MORNING THIS MORNING IT DID THE SAME THING, I HAVE NO PROBLEMS WITH THE CAR EXCEPT THIS,ECAN YOU HELP ME SORT THIS PROBLEM
October 24, 2016
  Followup from the Pelican Staff: If the engine is at operating temperature, the system will be pressurized. This is normal. - Nick at Pelican Parts  
Sar123 Comments: Good day, I have a 2008 e90 330i, theres a leak by the drivers wheel. I have to fill coolant every 2nd day. What could be the problem?
August 26, 2016
  Followup from the Pelican Staff: Sounds like a leak. I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty.- Nick at Pelican Parts  
Al Comments: Hi !
A friend buy for me a 320i E90 and now him tell me when start the engine find a crack on the plastic part of the radiator where leaking.
I intend to change the radiator but now i think what is the cause of that crack. Is posible after i change the radiator to crack again ?
Thank you !
August 6, 2016
  Followup from the Pelican Staff: Maybe. Just check if the thermostat and water pump are OK. if it is not overheating after replacement, you should be OK. - Nick at Pelican Parts  
Ariffin Comments: If the the coolant indicator lamp on with the red in color, the engine can not start. What should I do?
May 4, 2016
  Followup from the Pelican Staff: You didn't mention your vehicle type. It could be an overheating issue or a communication issue. Depends on the vehicle.

I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
ahmad Comments: I have bmw 325 2006 ' I noticed that the coolnet tank losing water about half leter weekly ,,what's the reason ?
April 30, 2016
  Followup from the Pelican Staff: The reservoir may be leaking. I would pressure test the cooling system. - Nick at Pelican Parts  
Alex K Comments: Hi, I have a 2010 328i wagon, Low coolant light came on... driver side footwell is wet. My guess is Heater Core- since I did a flush 2 months ago! possible a hose? How to tell if its a Denso or Valeo? Please Help Tnx.
March 28, 2016
  Followup from the Pelican Staff: I would assume heater core. The part brand can be determined using your VIN. Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Tdizzle Comments: Sorry, this is happening on a 2007 335i
March 23, 2016
  Followup from the Pelican Staff: Got it, thanks. - Nick at Pelican Parts  
Tdizzle Comments: I fill up my expansion tank because the coolant is low, I get immediate leaking on the passenger side of the engine and it drips down the engine side of the water pump and drips behind on the steering rack. Can not see down that far to observe the leak but the leaking occurs immeadiately and in a large amount. The water pump was replaced 5k ago.
March 23, 2016
  Followup from the Pelican Staff: I would assume it is a hose, thermostat or a connection to the water pump. There is a cluster of coolant hoses and components on that side of the engine. - Nick at Pelican Parts  
Chicksickofbeingrippedoff Comments: Hi my bmw 320i 2005 radiator hose came off and it came back with 3 pressure leaks on average how much would this cost to fix? From a student worrying ive been very much ripped a new one😤
March 22, 2016
  Followup from the Pelican Staff: I am not sure what the repair will cost in your area. Call a few shops and ask for a quote. It is also a good idea to have them confirm what the issue is.
- Nick at Pelican Parts
 
Evan Comments: Very useful article. I have an 07 e90 335xi that started to leak coolant down the passenger side of engine. I haven't found where exactly the leak is coming from but I am wondering which is the left and right side of engine you had mentioned. Which side of engine would passenger side be. I hope it's just a hose and not a costly pump. Thanks
March 17, 2016
  Followup from the Pelican Staff: Side of engine is as viewed when sitting in the driver seat. - Nick at Pelican Parts  
Ai Comments: I have a 07 335xi and I've have to keep on filling my cooling system every week. There no leak and my head gasket is good so I don't know to look for
March 1, 2016
  Followup from the Pelican Staff: I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty. - Nick at Pelican Parts  
Josh Comments: I have replaced the thermostat and tranny cooler due to both being cracked, it appeared that problems were fixed, now when driving and appears to be under pressure, I have a new coolant leak that appears to be coming from above front of transmission area not 100% sure could be blow back. Also fan kicks on right away from when car is cold started. Also when driving vehicle overheats within 10-15 mins of driving and expansion tank is bone dry. Please give me some advice
December 30, 2015
  Followup from the Pelican Staff: Could be a faulty radiator or hose. I would pressure test the cooling system. - Nick at Pelican Parts  
Al Comments: I have a 2009 328i BMW when you start the and while ideling engine runs fine but after driving It for 10 min and the park it idels higher run a little rough and had a slight whistling noise I flush the coolant system and bled it and still happens
May 2, 2015
  Followup from the Pelican Staff: Sounds like you have a vacuum leak. I would check the engine for vacuum leaks or cracked intake ducts. - Nick at Pelican Parts  
Nate S Comments: re: comment below: One other detail... It's not losing any pressure during the coolant cap pressure test. Wondering if that may indicate something in particular?
April 27, 2015
  Followup from the Pelican Staff: Ok got it. I responded to your other question. - Nick at Pelican Parts  
Nate S Comments: Thanks for the great write-ups! Looking for some input on a 2008 335xi 110k miles I bought used... Car was running rough and put into limp mode. Had it scanned to find P0016 cam/crank correlation. Replaced VANOS solenoids and cam sensors, did not fix. Before I could replace the crank sensor there is now a bad coolant leak. Took a look underneath to find coolant drip near both inlet/outlet of intercooler, can't tell if its coming down from radiator or from intercooler connections. Did a cap pressure test to find nothing coming from radiator at 20-25+ psi. Is there a chance that something like thermostat could be preventing pressure for getting to radiator or do I need to come to terms with fact I have an internal leak. Thinking head gasket, or turbo, or other??? Any suggestions on steps to diagnosis? THANKS!
April 27, 2015
  Followup from the Pelican Staff: Unlikely the thermostat won't block coolant flow. You probably have a leaking radiator. - Nick at Pelican Parts  
mdc Comments: Assenmacher BMW 350 adapter seems to be the one for E90.

Check this link:

http://asttool.com/detail_page.php?from_search=y&tool_number=BMW%20350&total=6&offset=0&stype=bymanf&manf=BMW&category=Cooling%20System%20and%20A/C

Click the blue button "Click here for applications" to the right of the image for listing of all models applicable.

BMW 345 description specifically says it is not for E90, but for older models.
February 20, 2015
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
Nate Comments: In the pictures, it looks like you're using Assenmacher Specialty Tools BMW 345 Radiator Pressure Adapter for BMW. I have a 2008 BMW 335xi, and I need to perform a cooling leak test, but the 345 adapter per Assenmacher's website and Amazon listing is only compatible with 1988-2005 BMW models 3, 5 and 7 series. Assenmacher has another BMW adapter BMW 350, but it's only listed as working with 2006 BMWs. Any idea on which adapter works with the e90? I've emailed Assenmacher, but no response thus far
January 20, 2015
  Followup from the Pelican Staff: I am not familiar with Assenmacher's part number scheme. If they say the 350 works, I would go with that. I am sure our parts specialists can figure it out with you. Give our parts specialists a call at 1-888-280-7799. They can help you find the right tool. - Nick at Pelican Parts  
46m3csl Comments: Hello, today my low coolant light came on for the 335i, removed the coolant and found almost no coolant. I added coolant but also found some brown sludge on the coolant cap, and then found the coolant hose that goes to the. Leaking near the clamp. What are your thoughts on testing this?
December 28, 2014
  Followup from the Pelican Staff: Start by pressure testing the cooling system. You could have an external leak. - Nick at Pelican Parts  
Nadir Comments: Hello,

I notice coolant between the cooling system flange, and the oil filter housing. however today only I noticed a large puddle at the bottom engine cover. in the same general area.
October 17, 2014
  Followup from the Pelican Staff: Could be a bad gasket on the flange. - Nick at Pelican Parts  
Brian Comments: Hello, my 2006 330xi seems to be going through coolant at a disturbing pace. I haven't noticed any liquid coming from beneath the car or under the hood. Are you aware of any other reasons this could be happening aside from a leak?
July 3, 2014
  Followup from the Pelican Staff: Could be a faulty head gasket. I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty. - Nick at Pelican Parts  
oz Comments: I have a 2006 bmw 330i I noticed antifreeze coming out from a grove in the expansion tank when I removed the cap. Is the expansion tank has like a release valve for overheating?. The car was parked with cool engine when that happend
November 18, 2013
  Followup from the Pelican Staff: The system is designed to release pressure if it gets too high. If there is not external leak the your coolant level is fine, this is likely what you saw. - Nick at Pelican Parts  

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