Rebuilding M54B25 on a 2001 525i (E39)
It all started when my E39 overheated when I was warming it up. At first I thought I got a thermostat failure since the temperature on the upper hose and lower hose were different, indicating the coolant flow is not right (the temperature on the upper and lower hose should be around the same). I called my friend, who is a mechanic, and he said the same thing: probably my thermostat had failed. He brought me a new thermostat, then installed it. However, the car still overheated when I warm it up. My friend brought me another thermostat and the problem still not solved. At the end, he told me it will be better to remove the head and get it checked whether it's warped or not.
After we removed the head, we checked it, and turns our my head has been warped. That's why something is going with my engine's coolant flow, as most of the coolant went to the combustion chamber and burnt away. But it doesn't end there, as two of six cylinders suffering compression loss, so we have to deal with it as well.
I was thinking, since I had my engine's head removed, it'll be better for me to do total engine rebuild to save me some money for repair in the future. We were checking the head and the block whether those can be repaired or not. Fortunately, my engine's head can be repaired, but my block can't be saved. The cylinder walls were too heavily damaged, and it will be cheaper for me to replace the entire block rather than repair it. Other than that, we're going to replace everything such as head gasket, valve cover gasket, vanos seals, piston rings, intake gasket, everything. The only things that left untouched are the camshafts, crankshaft, piston rods, and valves.
Looking for engine block replacement is not easy. Since the engine has been discontinued, we have to look it at junkyards. We have to remove it from the car, took it to the shop, and get it checked. If the block is not good enough, we returned it to the junkyard (yes, they accept full refund). Finally itt took us a month to found an engine block that still in a good condition. After that, we clean it and moved the engine's number from my old block to the new one. Then, we get things going. First, we're doing the engine block's first, get the piston rings replaced, timing chain (including the plastic thingy inside it), and everything else until the block is in a prime condition.
After the block finished, we're doing the head. First, we have it resurfaced so it is not warped anymore.
On January 22nd, finally the engine has been completed and properly installed under the bonnet of the E39. I start it up and let it sit for an hour, the temperature gauge stayed in 12 o'clock. Couldn't be more happier.
Unfortunately, there is another problem. Even though the engine is now perfectly healthy, the extra fan (which is the electric one) stuck at maximum speed. It sounded like crazy. Last time the extra fan stuck in this speed was when I drove this car for the last time before it's overheated. I think somehow the extra fan stuck in this speed thinking that my engine is still overheated. So, I'm going to check the electrical gremlins that connected to the extra fan. But for now, I am very happy that my car is now mended and I couldn't wait to drive it!