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Cooling System Leak Test

Pelican Technical Article:

Cooling System Leak Test

Nick Czerula


1.5 hours






Cooling system pressure tester

Applicable Models:

BMW X5 (2000-06)

Parts Required:

Engine coolant and additional parts will be needed 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 X5 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 the ground and properly dispose of it. Place a drain pan under suspected areas of leaks to minimize coolant spills. Six-cylinder models can develop coolant leaks toward the front of the engine, in places like the radiator outlet sensor, water pump and thermostat. Late 8-cylinder engines can have the same leaks as 6-cylinder models, with the addition of the leaking valley pan of the engine. A leaking valley pan on an 8-cylinder engine, will usually leak coolant down the rear of the engine, coming down around the bellhousing of the transmission. A pressure tester is the quickest way to find these leaks.

When pressure testing a cooling system, be sure the vehicle is cool and lacks pressure.
Figure 1

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

Once the cap is removed, install a pressure tester adapter (green arrow) to the coolant expansion tank.
Figure 2

Once the cap is removed, install a pressure tester adapter (green arrow) to the coolant expansion tank.

Pressurize the system to 1.
Figure 3

Pressurize the 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 the ground, you could have an internal leak. If you suspect a head gasket leak, you need to test the cylinder sealing via a leak down test. If coolant leaks externally, use a flashlight and follow the coolant to its source.

Coolant leaking down the right side of the engine could be the water pump or thermostat.
Figure 4

Coolant leaking down the right side of the engine could be the 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. The water pump has a weep hole where coolant commonly leaks from. It can be viewed using an inspection mirror. Coolant leaking down the left side of the engine can be from coolant hoses or from the oil filter stand/housing. Coolant leaking down from the radiator could be from the radiator or a radiator hose. To check a radiator hose, pressure the cooling system, then wiggle the hoses. While wiggling the hoses, check for a drop in pressure or a coolant leak. When looking for leaks at the radiator, inspect the side tanks on the radiator for signs of leaks or fresh coolant. Use a mirror to inspect the bottom of the hoses and connections at the radiator. If searching for the valley pan leak on M62 8-cylinder engines, I like to pressurize the cooling system, then inspect the areas under the intake manifold (green arrows). When the valley pan is leaking, there will be coolant puddled in this area. Mostly toward the rear, however I almost always see signs of it toward the front of the valley pan (inset).

Comments and Suggestions:
Ty Comments: ok thanks. i have already ordered a replacement coolant recovery tank/bottle. awaiting shipment of it.
January 22, 2018
  Followup from the Pelican Staff: No problem, let me know how it works out. - Nick at Pelican Parts  
Ty Comments: nick this is Ty with the 2006 BMW X5 E53 3.0i sport activity vehicle. I took car to shop for service to have two things done. One being the coolant flush and change of said coolant so there would be no air pockets within my system. the other was oil change done. while guy was pressurizing system doing check we discovered its leaking from bottom of the housing unit if looking at engine lower right portion of the housing unit is where leak ishe said it could be 1 of 2 things either the seals aren't seating properly or the housing unit itself is not good. I am about to order oem brand new coolant recovery tank. I am at a loss as to what are the seals for this entire system and more specifically what does the seals look like an is there any video or pictures which shows a properly sealed coolant recovery tank? thanks any insight would be greatly appreciated....
January 20, 2018
  Followup from the Pelican Staff: If the coolant reservoir is leaking, replace it. You can't repair it. - Nick at Pelican Parts  
Donnie Comments: I just happened upon your Site and what a great sites it is. I love the tech stuff aided with pictures and all of the parts you offer.

Your Site has been added to my favorites.

Keep up the great site. I will return.


BMW owner
March 27, 2016
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
sam rasphorn Comments: hi,congratulation...!i had job well done by yr. video,thanks for yr.helping by vedeos
October 5, 2014
  Followup from the Pelican Staff: Thanks - Nick at Pelican Parts  

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Page last updated: Fri 2/23/2018 02:35:22 AM