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2003 E46 325i, stroked to 3.0
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Discussion Starter · #1 ·
Background:
  • Drove car to break in engine after rebuild and conversion to 3 litres.
  • Entire cooling system refreshed except the transmission oil cooler (missed out on this as I was following Mango's guide).
  • Coolant low light popped up on the dashboard but temperature was at the middle.
  • Decided to stop the car in a parking lot. Coolant light remains lit, and temperature was still at the middle so I exited the vehicle to check for leaks.
  • Opened hood and found leakage right below the expansion tank and transmission oil cooler.
  • Went back into the car and saw the temperature has reached the red part and the red light was on. I am uncertain as to how long was the gauge at this point but I estimate I was looking at the leaks for around 30 seconds to 1 minute max.
  • Immediately shut off the engine.
  • After approximately 20 to 30 minutes of leaving the engine off, I checked the temperature on the gauge cluster test and it shows 124 degrees Celsius.
  • Towed vehicle to my mechanic and he replaced the transmission oil cooler. Pressure tested the cooling system, no leaks found.
  • Drove for 20 kilometres so far and temperature remained stable and no leaks spotted. Performance remain somewhat the same, but there may be a placebo effect in thinking that there is some sort of performance loss.

Questions:
1. I have seen contradicting views on overheating M54s. Some say that you face damage upon reaching overheating, while several others had experienced no issues despite overheating for around 2-3 minutes. Based on the chronology I have shared, how likely is the engine damaged?

2. Since the result of pressure testing the cooling system is fine, is it safe to assume that there was no damage to the engine?

3. I will check the coolant level first thing in the morning tomorrow. If coolant level remains at max, safe to assume no damage?

4. Am I correct to say that engine damage symptoms will show up easily and very quickly if there IS damage? Approximately how many mileage will the symptoms appear? And what are the symptoms?

5. Do I still need to perform a compression test after cooling system pressure test is ok? Any other test to check engine health?

6. Since I have gotten this engine rebuilt, will there be any degradation in performance since it has already overheated once?

7. Since I stopped the car before the temperature gauge reached red, and it only turned red while idling, is it safe to assume that there is no or minimal engine damage since the engine is not being pushed.

Sorry for the list of questions, I have searched through numerous topics posted in this forum as well as on bimmerfest but everyone's experience seems to be slightly different.

Quite disappointed that I have refreshed almost every part but never thought the transmission oil cooler would have been the cause of a coolant leak.

Appreciate any answers or opinions. Thank you.
 

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1. I have seen contradicting views on overheating M54s. Some say that you face damage upon reaching overheating, while several others had experienced no issues despite overheating for around 2-3 minutes. Based on the chronology I have shared, how likely is the engine damaged?
There is a chance that the head bolts threads in the block weaken, then combustion gas will enter the coolant in the future.
2. Since the result of pressure testing the cooling system is fine, is it safe to assume that there was no damage to the engine?
Inconclusive. Coolant tested at 18 psi, but combustion gas is around thousand psi, so you just have to wait and see if the hoses got hard indicates gas entered the coolant.
3. I will check the coolant level first thing in the morning tomorrow. If coolant level remains at max, safe to assume no damage?
See 1. But continue to check for next few weeks and hope for the best.
4. Am I correct to say that engine damage symptoms will show up easily and very quickly if there IS damage? Approximately how many mileage will the symptoms appear? And what are the symptoms?
Extra hard coolant hoses; misfire with coolant entering combustion chambers, more white smoke at tail pipes.
5. Do I still need to perform a compression test after cooling system pressure test is ok? Any other test to check engine health?
It's hard to check because the leak can be very small, but it will get worst with more mileage.
6. Since I have gotten this engine rebuilt, will there be any degradation in performance since it has already overheated once?
Only the head and block threaded holes are affected. Can be fixed easily.
7. Since I stopped the car before the temperature gauge reached red, and it only turned red while idling, is it safe to assume that there is no or minimal engine damage since the engine is not being pushed.
See 6.
 

· Registered
2003 E46 325i, stroked to 3.0
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122 Posts
Discussion Starter · #9 ·
Then maybe someone added grease on the cap o-rings for smoother installation. If no substance like mayonnaise in the tank then no sign of engine oil in the coolant, yet.

But wait - show pic of the cap bottom side below the oring.
Bottom of the cap is fully clear.

Checked dipstick and engine oil cap and no mayo too.
 

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11,962 Posts
I don't think it was the bad tranny cooler, but a bad connection popped out and dumped the coolant on ground.
The cooler is held on to the bottom bracket by the locking clip, and this clip was not in the groove and the hot higher coolant pressure pushed the cooler away from the 2 ports, leaked. Man, little thing over looked leaded to headache, no fun.
 
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