Found coolant leak/temp fluctuation I've been chasing... looking for thoughts

[sapote]

I think the DME sampled the temperature and averaged out every 5 seconds or so, as there’s no benefit to do the average calculation faster than that. Obviously it doesn’t display the raw noisy sample data. But I thought the M3 don’t use buffering for the gauge as non-M cars.
As about the leak affected the pressure and temperature, I thought you had a very small leak that very hard to find, which should not change the pressure. A small leak as 10cc in 30 minutes should not change the operating pressure or temperature.

[heinzboehmer]

Go take a look at the inside of your water pump pulley with a mirror. My pump leaked through the bearing and there were a lot of specks of coolant on the inside of the pulley. Could also be the gasket between the pump and block.

[Obioban]

Coolant mist spray is very often the pump. I bet when you pull it, it’s not OE.

[JustAWhisper]

I think the DME sampled the temperature and averaged out every 5 seconds or so, as there’s no benefit to do the average calculation faster than that. Obviously it doesn’t display the raw noisy sample data. But I thought the M3 don’t use buffering for the gauge as non-M cars.
As about the leak affected the pressure and temperature, I thought you had a very small leak that very hard to find, which should not change the pressure. A small leak as 10cc in 30 minutes should not change the operating pressure or temperature.

I think you are correct on the DME, but I did look into the buffer issue a while back and I learned the M3 is buffered, just in a much smaller range, 90-100C. Non-M's are 85-115C iirc. Without knowing the cooling system design and doing the math, it's hard to say for certain if a small leak is enough to cause the temperature difference I'm seeing in the gauge or not. I just know it's theoretically possible and it makes sense to me. You may be correct and it's just gauge issue. Once the cooling system is completely fixed I'll be able to find out for sure.

Coolant mist spray is very often the pump. I bet when you pull it, it’s not OE.

That's what I'm thinking, too.

[sapote]

I think you are correct on the DME, but I did look into the buffer issue a while back and I learned the M3 is buffered, just in a much smaller range, 90-100C. Non-M's are 85-115C iirc.

Interesting. If M cars have buffering (quantization to be correct) as you said, say needle stays at 12 o'clock for actual temp in [90:100C] range, then it jumps to the next position, say 1 o'clock for [101:110] then we should see a jumpy needle and not a continuous moving needle. Do people see a smooth moving needle to jumpy needle?

[JustAWhisper]

Interesting. If M cars have buffering (quantization to be correct) as you said, say needle stays at 12 o'clock for actual temp in [90:100C] range, then it jumps to the next position, say 1 o'clock for [101:110] then we should see a jumpy needle and not a continuous moving needle. Do people see a smooth moving needle to jumpy needle?

It's smooth. The needle pins 90-100C to 12 O'clock, but outside of the range it has some sort of sliding scale.

Also, I got the water pump out. It's a Geba (not OE).

[heinzboehmer]

Also, I got the water pump out. It's a Geba (not OE).

Was it the source of the leak?

[sapote]

It's smooth. The needle pins 90-100C to 12 O'clock, but outside of the range it has some sort of sliding scale.

Also, I got the water pump out. It's a Geba (not OE).

1) So in order to see the needle jumps, the temp must had changed from 100 to 103 or 105, and not just 100 to 101. 3 or 5C is not small.
2) did you feel any radial or axial plays on the old pump?