AlexB 24 Report post Posted September 8, 2023 Hi All, Time for my annual post with an annoying issue. A Friend of mine recently made a purchase of (against my strongest recommendation) An E89 Z4 with the infamous N54 power plant. Along with this came reliability issues as one could imagine. Being the mechanic/BMW guy of the friend group I have been left with the task of repairing said issues. First the roof gave up and that only took 18hrs and 2x boxes of beer to fix. Then along came a coolant leak, wondering if any N54 / E89 gurus on here could lend some advice. The car drops almost all of its coolant after a good thrash, it leaks from the passenger side under the radiator right where the drain is. Being a tight engine bay its almost impossible to see anything down there or get a hand down to check for loose pipes/ connections while hot, let alone the 3rd degree burns you'd get. I've had the car in at my workshop on a hoist and pressure tested the system up to 20psi (a little over operating pressure) hot and cold, no leaks. Once returning from a long/hard drive turning the car off, the car starts leaking, sounds as though the electric water pump stays on which I can imagine it should to try cool the turbos, although it sounds like its under a lot of load. It drops almost all of the coolant and once its all leaked out, pump stops. Assuming the radiator drain was the issue I replaced it today as it did have worn o-rings, hoping to rid this issue and return it to the owner. But once I got home in it this afternoon it decided to F**k my Friday night again... I immediately got it on the scan tool to see live values of pumps and thermostat etc. but by the time it loaded it had finished its leak cycle. I tried to force activate the pump and electric fans however nothing happened. At this point i'm very lost in the diagnosis as it doesn't seem to be pressure related issue, in fact I can remove the coolant tank cap completely while its leaking and it doesn't stop. Very lost on this one, any help is massively appreciated before, out of confusion and anguish I sell her a whole new cooling system... Quote Share this post Link to post Share on other sites
