I recently purchased a used M4 and after a bunch of diagnosing and sleepless nights I have decided to share my story/progress and entertain you fine people. *This vehicle was purchased from Copart*. And while I can certainly afford a new or used M4 from better sources than Copart who doesn't love a good project car? My thought process was if I buy a reasonably cheap M4 by the time I’m in used car territory I'll have a built or at least have a FBO car.
The previous owner of this fine piece of German engineering seems to have been a 20 year old kid from Iowa with a questionable driving history. I say that with confidence because upon delivery of the vehicle in the trunk I found a repair estimate of a 2017 Mercedes Benz C300 which judging by the estimated repair cost I assume was totaled out by insurance. There was also a letter from his insurance which in summary was them informing him that they were nearly tripling his monthly premium. Then an estimate for fixing passenger side quarter panel damage to the M4 which was now in my possession.The newest damage to the car came in the form of a nearly destroyed front bumper in desperate need of replacement, a bent control arm and a destroyed oil cooler. I figured suspension work would be straight forward. I ordered the control arm from my local BMW dealership and was able to install it no problem. I ordered a new oem bumper online and arranged to get it painted at a local shop and removed the old one.
This is where my trouble began. Somewhere between the copart lot and my home in New Jersey they keys to the vehicle were lost by either someone at copart in davenport Iowa or the driver of the truck who delivered the car and so after not being able to get the car into neutral I used wheel dollies to push the car into my driveway. I'm leaning towards copart error in loosing the keys at this point but I ordered a new key from BMW, charged the battery with the fancy c-tek lithium charger needed for these cars and after letting it sit overnight I threw in new plugs gaped to .020 and new coils in the car. After receiving the new key I got all excited to start her up and was quickly disappointed when she didn't start up.
No problem a little diagnosis never hurt. (Side note the oil cooler is still not here at this point however it is bypassed using a hose and hose clamps to the inlet and outlet hose for the oil cooler.) I get in the car, scan for codes and find nothing, but I do see that the oil change is due in 2000 miles. No problem I'll change it now. I pull the drain plug and instantly realize there is coolant in the oil.
I let it drain for a good hour, change the filter and figure lets see if this is as bad as it seems. I’ll put oil in, crank it a few times to get oil circulating, and then drain the oil again, and see if there is less coolant(milkshake looking oil) that comes out.
Fast forward to the next day and a few cranks later the oil looks slightly better? Still coolant in there but probably less. At this point I take a step back to research if there is an oil to coolant heat exchanger in the M4. That's an obvious no so I figure there was coolant left in that hose and other areas of the engine that could cause the oil to still look like a milkshake after cranking the engine a few times but i start to accept the fact that I'm probably looking at a serious engine rebuild and maybe even a new motor at this point. But what could it be? The oil filter housing has coolant passages that could mix oil and coolant but why would that randomly fail at 40k miles? A head gasket on an s55 failing?? Never heard of that one.., A completely wrecked motor that cant be rebuilt or saved maybe?? A trip to the auto parts store later and I'm ready to do a compression test.
This is where things get really bad. I disconnect the injector wire, pull the new spark plugs, and hook up the compression tester. I crank the engine over 6 times, look at the psi and its reading 0. After checking to make sure it was connected properly I try again and get 0 psi. Then on a 3rd try I manage to get 90psi. That’s really low obviously and I start thinking i have valves stuck open, maybe valvetronic doing things only BMW engineers understand. But why would it read 0 a few times and suddenly read 90 psi? Who knows but lets continue testing this thing. Long story short basically every cylinder had random 0-10psi readings and then a few 90-130 psi readings but at this point I know there’s something weird going on. I’m still unsure if there is a special compression test procedure for the S55 motor but at this point I understand that unless my timing is way out causing no compression my piston rings are fried and cylinder walls likely destroyed,(this explains the low compression but not the coolant in oil) the head gasket is very very blown (which does explain coolant in oil and could explain the low compression but in my experience compression never gets that low from a head gasket) or my motor is blown and destroyed in ways I can’t fathom (that explains everything from no start to little to no compression and coolant in oil). Here’s the really weird part of the whole coolant in oil situation, there coolant tank is FULL. We will see for sure when I’m home next week and drain the oil for the 3rd time. I guess a leak down test never hurts but this thing is a lot more confusing than the m52 I remember and loved so much. I welcome all input and ideas as to what’s going on with what is currently a very overpriced paperweight. Here are some pictures of the car I'll add more photos as work on it continues.
https://photos.app.goo.gl/jHHYU3om9igtX4RTA