Coolant Pressure Test - Failed. Internal Leak
 

Got a new thermostat and temps are still a bit elevated on the OBC (96c)

Did a coolant pressure test and lost 1 psi in the first 5 minutes, and losing more as time went by.

Looked all over and no leaking. Looks to be internal.

Crap! Head gasket? Am I screwed?

What PSI did you pump up the cooling system to?
I would check the small coolant lines and switch valves that run to the heater for a very small leak, first. Then the expansion tank, lines, hose clamps,etc. Our rads seals are a high failure item and will hold what seems like a Qt before dripping.

A quick engine compression test will show head gasket issues. Are you getting any water entering the oil systems and then down to the oil pan? Shows up as white milky stuff everywhere!

I don't which is worse a head gasket or a heater core, both in my book is time to move on and get another car.

A definitive test would be to get a combustion gas in the cooling system test kit.

Are you sure that air is not leaking from the interface between the pressure tester and the car? 1psi over 5 minutes is not much.

Regarding high temp, are you sure there is no air in the cooling system?

Also, which of your two X5's is this on?

Sorry guys, its on the 3.0.

Pumped it up to 15psi.

Heater core is bypassed currently. The heater valve supply line and heater core outlet line are joined via a barbed connector.

No oil in the coolant, no coolant in oil that I can see.

No air in cooling system i believe, its been bled to hell already with a lot of new parts which is why I had it pressure tested. Coolant temps cycle up and down with thermostat activation, temps are slightly elevated though.

No leaks at the pressure tester cap but will check more thoroughly, maybe soap it up and see if there is any slight leak.

Was checking all over the engine and not a drop I could see. Removed the underbody cover and the air cleaner assembly to get a better view of the hoses.

To test for leaking cooling system on the V8, pressurize the system to 22-psi, wait for 2 minutes and the system should not have lost more than 1.5 psi. It's perfectly normal to loose more as time progresses!

X5o, thanks for the info. I had been of the impression that pressure should hold steady?

It never does but the drop should be only 1.5 psi in the first 2 minutes. Here's the official BMW doc on how to test.

BMW Workshop Manuals > X Series E53 X5 3.0i (M54) OFFRD > 2 Repair Instructions > 17 Cooling System (M54) > 0 Coolant, Checking Cooling System > 4 RA Checking Cooling System For Water Leaks > Page 828

Checking pressure drop in cooling system:

- Remove cap on expansion tank. Attach special tool 17 0 002/17 0 005 .

- Build up gauge pressure of 1.5 bar, wait approx. 2 minutes. Cooling system is impervious to leaks if pressure drop is max. 0.1 bar.

From the above, you can infer that pressure drop is expected but only 0.1 bar (1.5 psi) in a span of 2 minutes. And if you wait for 5 minutes, there will naturally be further pressure drop BUT no coolant loss. Conversely, if you wait less than a second, you will not notice any pressure drop :D And if you wait for a whole day, you will see significant pressure loss BUT no coolant loss.

Well it depends what you mean by steady. At 22 psi, dropping < 1.5 psi in 2 minutes apparently is steady enough (I don't know what his reference is for that spec, but I'm not surprised a non-zero pressure drop is acceptable).

That's what I was suggesting above - that your 1 psi in 5 min is not much.

On the other hand, if the pressure drops, the air you pumped in there must be going somewhere. First guess would be at the pressurizing interface. Next would be the pump/gauge itself. Somewhere down on the list of likely scenarios would be that you're forcing coolant past a failed head gasket. Without any other reason to think the worst, I would not expect that one to be true. But if you convince yourself it is toast and want someone to haul it away, PM me!

Good luck finding the problem.