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By Fox 3
I have a 20 year old BMW X5 with the straight six M54 motor. 205,000 miles. For first 80,000 miles it burned zero oil.

Recently it was burning 1 qt every 600 miles and then I switched to Torco ring sealing oil and consumption was cut in half.

The engine was running rough at idle with shakes at stop signs for the last 50,000 miles, I replaced everything including motor and tyranny Mounts, no dice, then I recently had a check engine light on a long drive and a code for a misfire on cylinder 6. The mechanic said the plugs were fouled and recommended replacing the ignition coils and plugs. The ignition coils were 20 years old. Plugs replaced on schedule every 100,000 miles.

Now the engine is purring smooth as a kitten, no more shakes at all. But the mechanic did cylinder compression tests before replacing the coils and plugs and all the cylinders were at 175 except for cylinder #1 which was at 150. Seems like a big delta.

Should I ignore this or do something preemptively?

TIA. Checked various forums and could not find a straight answer.
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By N_Jay
Have it rechecked wet and see if it is rings or valves.

Rings are just wearing out and you can drive it till it runs unacceptably.

Valves will burn, so get the head done before it becomes unserviceable.
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By Scott at Team Harco
It might be worth checking again 'wet', as N_Jay suggests. If compression comes up in #1, it would be clear indication of worn rings. That is the most likely cause, as it is. There's pretty much nothing that can be done preemptively. Frequent oil changes and maybe a step up in viscosity can help. I.e. if using 40 wt oil, go to 50w.

A leak down test will be even better than another compression test. It will identify where the compression loss is going. It may be valves or rings.

Maybe dump in some 'piston ring in a can'. :byewave:
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By XR4Tim
That's a little bit more variation than you'd typically like to see on cylinder 1, but 150 PSI is still plenty to produce adequate performance. I would concur with a leakdown test to indicate where the lost compression is going and determine the course of action.
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By Fox 3
Been doing some research about the M54 engine. This guy made a pretty interesting post:

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The above points to one of the reasons the older style rings fail to perform their primary duty (oil control ring shown above) by what is largely considered a design flaw.
In a perfect world, the oil always gets hot, it is changed often, the car always runs within 1-2° of center fuel trims etc. The oil control ring will not clog up ("Coking") and will retain good tension to wipe the oil down towards the sump with each and every pass.

In reality the coking starts to happen incrementally and because of the added layer of hardened oil, as it starts to build up and the upper and lower edges of the oil control ring do not seat fully against the cylinder bore. As the buildup increases more and more of the ring is pushed away from the bore. This in turn lets minuscule amounts of oil get past.
This becomes a vicious cycle of blowby and the problem starts to accelerate.
The two upper rings are for compression and while they will wipe some oil, it's not the design or function of those two and they don't do a very good job of controlling oil past the rings and into the combustion chamber.

For most trying to combat oil consumption we suggest Liqui Moly Engine flush (sometimes multiple applications are needed) followed on with a couple of rapid (lets say 2,000 miles each) With Liqui Moly Leichtlauf 5-40. This oil was developed with engines like the M54 engine family in mind. It has an additive that aids in cleaning out deposits such as those found on oil control rings.
Once cleaned, just maintain with the same oil.

Not everyone will be successful with the above cleaning process, but because it does NOT require any engine tear-down, what do you have to loose?

Unfortunately the oil coking on the oil control rings is NOT uniform. It builds higher in some spots and lower on other spots around the circumference of the ring. Over time the spots with little to no buildup still continue to have contact with the bore and continue to wear. Conversely the spots with high buildup are isolated from touching the bore.

Cleaning the engine with additives (in the above) can see the ring become clean. However now the ring sometimes no longer perfectly true. (the longer you wait, the worse this can become) With some spots having 100% contact, and with the spots that were touching before (no buildup) being worn. The ring is now free, but no longer round and true. Hence why it's important to get to the issue of keeping the inside of the engine clean from an early time and NOT waiting until you consume a liter of oil every 400 miles.

This is but one of the reasons a M54 engine consumes oil. (Yes there's two folks) The other being a completely functioning and healthy CCV system. That's more than the CCV itself and the two hoses attached to it. It's also the drain-back tube and a clear outer perimeter of the oil dipstick tube.

In addition for the CCV system is it's ability to function: There are no wires or electric drives attached to the CCV.
It runs on one thing ONLY; Engine vacuum. If you have a vacuum leak even a brand NEW CCV system will NOT function correctly. It relies on healthy vacuum to have it function.

EDIT: The newer style rings have much larger holes, to allow for better shedding of oil after the engine shuts off. Most of the "coking" will happen within an hour or two of engine shutdown.


Anyone use the Liquid Moly or other cleaners? Someone else also commented on Marvel Mystery Oil being really good. Lately I have been using Torco ring sealing oil and it seems to have cut consumption by maybe 50% over Mobil 1. Not sure how it works. I'm slightly nervous about pouring something directly into my engine's oil system.
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By Scott at Team Harco
I was going to suggest Marvel Mystery Oil, but have not used it for this specific issue. The Liqui Moly treatment seems reasonable. If it were me, I'd search out more information and if no major complaints, I would consider trying it.

Sea Form is another option. Do more research regardless of your direction.

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