Pressure Test - Cooling System - ? PSI

[Jimmy535i]

I have a slow leak somewhere in my cooling system on my 1990 735il. (250k miles). I want to run a system pressure test in order to find the leak and have borrowed the tool from my brother to do it. Anyone know what is the correct PSI to use for running this test? Any other advice would be great too.

Thanks
Jim
90 535iA 141k
90 735il 250k

[Rick L]

Correct psi is 30 to 45. I usually max out at 50 to 55 psi (slightly overcharged). Make sure you don't put more than 70 psi! Also, make sure you check it with engine running and A/C on. Also, you must check it at low-pressure port which is the one that runs to A/C compressor.

I have a slow leak somewhere in my cooling system on my 1990 735il. (250k miles). I want to run a system pressure test in order to find the leak and have borrowed the tool from my brother to do it. Anyone know what is the correct PSI to use for running this test? Any other advice would be great too.

Thanks
Jim
90 535iA 141k
90 735il 250k

[shogun]

Right expansion tank cap?
Just check it, there was an exchange. I had my radiator 'exploded' by too high pressure.
click here

[Jimmy535i]

Right expansion tank cap?
Just check it, there was an exchange. I had my radiator 'exploded' by too high pressure.
click here

[Jimmy535i]

Rick, Thank you. I will try 30-45 psi and listen for leak with engine off first.

[Bill R.]

then it pops off and release pressure at 2 bars.... Bmw specs for testing pressure is 1 bar on the 735 or 14.5psi and 1.5 bars on the 750 or 21 psi..
I would test it cold and then warm it up and test it warm... sometimes leaks that occur when cold don't show up when hot and vice versa.. When warming it up leave the expansion tank cap loose so it doesn't build up pressure

I have a slow leak somewhere in my cooling system on my 1990 735il. (250k miles). I want to run a system pressure test in order to find the leak and have borrowed the tool from my brother to do it. Anyone know what is the correct PSI to use for running this test? Any other advice would be great too.

Thanks
Jim
90 535iA 141k
90 735il 250k

[Bill R.]

You're talking about the engine cooling system and Rick is talking about the air conditioning , 2 entirely different things.

Rick, Thank you. I will try 30-45 psi and listen for leak with engine off first.

[Jimmy535i]

Bill: Thank you for the information.

I was talking about the cooling system. I was planning to test this weekend also.
I replaced the upper radiator hose last year and the thermostat last week.
I have a new water pump that I got from BMA - not installed yet.

My AC sysem is fine. I converted it
to R-134 2 years ago and it will freeze you out it is that cold.

[Jimmy535i]

735 - 1 Bar 14.5 psi - Thats the ticket - Thank you

[Jimmy535i]

I ran the pressure test and found the source of my slight coolant loss.
It turns out I needed to replace the hose from the thermostat housing to coolant reservoir. (it had a small crack) I ended up replacing a few other hoses and the system is now leak free. I replaced the thermostat also and bled the air from the system. The car ran fine for about 10 days (needle dead center) Yesterday when driving in slow traffic with the AC on the needle started moving above center again. (outside temp was about 90F)
It looked like I was ready for an overheating episode. I pulled off and
shut car off before temp went past 3/4.

Could my waterpump be kaput ?
Could my fan clutch be kaput ?

I have both parts on my shelf. Got them from BMA.

Any insight would be appreciated.