Lost Oil Pressure? Don't Lose Hope
I know with M5x and S5x engines there has been some documented issues with the oil pump nut backing off and causing loss of oil pressure and in most cases that include non-enthusiast drivers they continue to drive the car with the bright red oil dummy light on until the engine "starts actin' funny."
Now I am here to share my recent experience with a 2001 330i I purchased that had this exact problem to reassure those with similar issues that not all hope is lost.
If you were smart enough to shut your engine down as soon as the red oil light came on then kudus to you, simply repair your oil pump and keep truckin' but if you, your wife, gf, mom, previous owner were not so diligent then read on and be prepared to do some wrenching.
1. DO NOT attempt to repair the oil pump to restore pressure just to see how it will run. Most likely you have metal shavings setting on your bearing surfaces that will do more damage if you restore pressure and circulate them!
2. Perform a compression test. Healthy M54 compression should be at least around 180psi or greater.
3. If you have access to a boroscope then check the condition of your cylinder walls.
4. Drain all your oil and check for metal.
Here's where it begins to suck.
5. Pull your oil pan, remove the oil pump and windage tray.
6. Pull rod caps and main bearing caps to check for damage to bearing surfaces. If they are ok apply assembly lube and reinstall. Be aware that rod bolts are one time use so you will need to purchase new rod bolts. (My rod bearings were burned up but my main bearings were ok.)
7. Pull your valve cover and inspect your cam bearing surfaces / caps and lifters (In my case the bearing surface / caps 6 & 7 on the intake had completely scored up my intake cam shaft turning the caps black from the heat and cracking one in half not to mention just about all my lifters had collapsed.)
~ At this point if your compression test is healthy and you have not found any evidence of damage to any bearing surface or metal in your oil then wash down your valve train with a quart of fresh oil, repair your oil pump and button everything backup. Otherwise you have 2 choices. Replace the entire engine or rebuild it. (I chose to rebuild it)
SO YOU FOUND DAMAGE AND/OR HAVE BAD COMPRESSION
8. Pull the cylinder head off the engine and at the very least have it cleaned in a parts washer to remove all metal shavings. Make note of any damaged parts and order replacements.
9. Remove the pistons and rods.
10. Purchase a 89mm Flex-Hone 240 Grit cylinder hone. Use this with a power drill to de-glaze your cylinder walls and restore crosshatching.
*Be sure to use hone oil or a light conventional oil and clean the bore many times with soapy water when you finish.
11. Install pistons with new rings, rod bearings, and rod bolts.
12. Reinstall your oil pump, windage tray and oil pan.
13. Reinstall your cylinder head using a new head gasket.
14. Assemble the remainder of the engine using new gaskets, seals, and orings. (This is also a good time to do other maintenance such as the oil filter housing gasket, VANOS seals, etc.)
15. In preparation for breaking in your new rings and bearings install a new oil filter and fill your crankcase with a conventional oil that has a high Zinc (ZDDP) content, (I used Shell Rotella T SAE 30).
BREAK IN PROCEDURE
This tends to be an issue that mechanics argue back and forth about. So here's my take.
16. Start your engine and allow it to warm up.
17. Rev your engine to 2-3k with a few 10-20 second revs to 5-6k in between for about 20-30 minutes.
18. Immediately change your oil and filter still using the same conventional oil you used for the initial break in.
19. After about 500 miles change your oil again to the synthetic oil of your choice.
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