2004 Z4 2.5 M54 Compression Test

[BMW Spartanburg SC]

See attached the results of compression test on a 2004 BMW Z4, E85, with 2.5, M54 engine. 126,000 miles. The engine was dry and cold. The pictures are labeled with cylinder number. I thought I would post this. The compression test is a simple test and not too time consuming. Remove all the plugs and pull the fuel pump relay. I bought this car recently and wanted to check the compression before proceeding with other repairs.

Oh my the water pump, there is a support frame directly in front of the water pump, so you must loosen the left motor mount and slightly raise the engine to get the water pump out. Clearly an oversight, I think. At least it has an electric radiator fan, so there is nothing mounted to the front of the water pump. Cheers!

2004 bmw z4 2.5 m54 comp test cyl 6 view 2.jpg (87.33 KiB) Viewed 289 times

2004 bmw z4 2.5 m54 comp test cyl 5 view 2.jpg (81.23 KiB) Viewed 289 times

2004 bmw z4 2.5 m54 comp test cyl 4 view 2.jpg (79.02 KiB) Viewed 289 times

2004 bmw z4 2.5 m54 comp test cyl 3 view 2.jpg (90.19 KiB) Viewed 289 times

2004 bmw z4 2.5 m54 comp test cyl 2 view 2.jpg (80.77 KiB) Viewed 289 times

2004 bmw z4 2.5 m54 comp test cyl 1 view 2.jpg (87.95 KiB) Viewed 289 times

[raymond.harper]

There is no attachment to your post. You need to give any documents time to upload before you post.

[Mike6]

I always thought a compression test had to be performed on a hot engine

[j3nks79]

What are you trying to find out?

[BMW Spartanburg SC]

Dear Mike6, my understanding is that a hot engine would potentially give the best readings since metal parts have expanded. If I wasn't satisfied with the 'cold' readings, I would proceed to check with hot engine, putting small amount of oil in cylinders, etc.

Dear j3nks79, since I recently bought this car, I was trying to test that the engine was 'healthy' and no low compression on any one cylinder. I didn't do a leak-down test since its more involved, need compressed air and some extra fittings...

2004 BMW Z4.jpg (129.29 KiB) Viewed 236 times

[Joez4]

I always thought a compression test had to be performed on a hot engine

I'm no expert but I always thought removing plugs from a hot engine isn't a good idea due to the potential of stripping the threads

[BumpyZ4]

I always thought a compression test had to be performed on a hot engine

I'm no expert but I always thought removing plugs from a hot engine isn't a good idea due to the potential of stripping the threads

Nope, the aluminum heads expand more than the steel spark plugs when hot so should come out easier.

[grannyknot]

Those numbers look pretty good for a cold engine, did you also remove the spark plugs and wire the throttle open? Doing that eliminates any resistance to the incoming and out going air and gives a more accurate reading.
A reading on a hot engine will give you the most accurate numbers of that engine but a cold reading should still show if the readings are consistent, yours are.
A wet test, squirt of oil in each cyl will just let you see how worn the rings are, a leakdown is done if you find a cyl with low numbers and want to pin point where the leakage is happening.

[BMW Spartanburg SC]

Thanks you all,
I did remove the spark plugs but didn't wire the throttle open.