This prevented the damage from being worse - bent valve, that sort of thing. I came out in the morning, the piston raised as the valve closed, and the coolant filled the combustion chamber and the engine hydro-locked on the starter motor. My working theory is that while my head was cracked, I just by chance turned the engine off when the valve was closed, then one day I turned the car off with the valve open and there was nothing to keep the coolant from being sprayed into the cylinder as the engine cooled. You will see a photo of a crack at the valve seat of an Exhaust Valve where the crack is between the seat and a water passage. You should Google BMW M50/M52 CRACKED HEAD, then click on the Images tab. One morning I went to start my car and the piston hit a hard stop because the cylinder had filled with coolant over the weekend. I had no other symptoms, except for the mysterious loss of coolant. When I had a cracked head, I noticed that I was adding about half of the expansion tank about 4 to 6 weeks apart. BUT, if you have a cracked head, it wold become apparent through repeated need to fill the radiator. The only affect you would see in the early stages would be coolant loss that would be so slight as to not even produce steam at the tailpipe. A crack in the head would allow coolant to seep directly into the exhaust stream, no coolant would go to the oil, and no oil would go to the coolant. I didn't think it was the head, especially since the oil cap had no yellow sludge on it and the levels all seemed to be right. Yep, I topped off the tank with a 50/50 mix of BMW coolant and will make sure to check it more regularly. You might smell it, but you will not see it. You will see pictures of a small crack that happens to a wall that separates an exhaust valve seat from a coolant passage, coolant goes directly into the exhaust stream and you cannot see it. Google, BMW M50/M52 CRACKED HEAD, then click Images. I took the plugs out and a cylinder full of coolant came out of the #3 cylinder. One morning my engine hydro locked during Engine Start. No overheating or anything, just coolant loss. I made repairs to the cooling system, but noticed over the next several months that I was consuming coolant. It lasted about 6 miles to the summit of the mountain and I coasted to the bottom of the hill so AAA could come get me. I had the cooling system explode one night on a mountain road and I went a 1/4 to a 1/2 mile where I could put the upper hose back on and fill with water. My car had the famous Cracked Head, it took months to figure put why the coolant was leaving. The radiator cap has a pair of o-rings that get flat sides and they do not hold the fluid in very well. If you are going below the line but it takes several tanks of gas for this to happen, then you have one problem, but if you are below the line every weekend and a tank of gas or so, then you have a different problem.īut, the specific answer to the question is that the coolant should be at the KALT line when the engine is stone cold. If you have not topped up for several weeks, or months, then being low is not a big deal. If you are frequently topping up to the line, then you need to figure out why. On a cold engine, the level should be at the KALT line. Having the coolant below the line isn't as important as how quickly, or how often, it gets there.
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