Archive | December, 2015

’91 BMW 318is Upper Oil Pan Replacement

11 Dec

WARNING: This post has nothing to do with audio. If that’s all you’re here for then carry on. However, when I was searching for similar guides online when I had to perform this procedure, I found very little information so figured I should contribute what I have since learned to the grand how-to database that is the Internet.

As the title suggests, I recently had to replace the upper oil pan on daily driver, a 1991 BMW 318is. This car is surprisingly hard to find consistent documentation on regarding repair procedures for, as it is a bit of a Frankenstein. This is the last year BMW used the e30 body style for the US 3 series before switching to the e36 in 1992 (I think there may be an exception for the convertible which stayed e30 into 1992, but whatever). Anyhow, the 318i was originally based around the venerable M10 4-cylinder engine. Having been in production since 1962, the wonderfully designed M10 was clearly showing its age. In 1988, BMW replaced the M10 with the M40. Being a 4-cylinder, SOHC engine, the M40 was very similar in output to the M10, so not a very exciting change other than being a more “modern” engine with features such as hydraulic tappets (I’m simplifying this history quite a bit, but you get the point. If you want a full history and description of every BMW engine variant, wikipedia has a surprisingly rich amount of info on the topic).

In 1989, BMW seemed to realize the 318 could be a lot more fun with a little added excitement under the hood. Enter the M42, a 4-cylinder DOHC 16 valve engine. While I haven’t actually read this anywhere, it seems BMW had planned this engine for later vehicles (the e36 chassis), but decided to go ahead and throw it in the e30 and introduce the 318is starting in 1989. Why do I think this? If you look at any e30 repair manuals–Chilton’s, Bentley Publishing, etc.–you will not find even a mention of the M42 (nor the M40, for that matter). So the lucky owners of the e30 318is (and the 1988-92 318i) get to reference two breeds of repair manual: e30 manuals cover the suspension, electrical and body while we must consult the e36 manuals for engine maintenance and repair. So that’s fun.

The M42 features a two piece oil pan, lower and upper, with paper gaskets between the two pans and between the upper pan and the crankcase. Among what seems like a gazillion bolts holding the pans in place are six bolts inside the upper pan holding the front of it to the crankcase. Due to extreme temp changes and vibrations, combined with low torque specs due to the aluminum’s rigidity, or lack-thereof, these bolts often come loose, allowing the pan to shift and lose its seal, sucking air into the oil pickup. That’s bad. Your oil pressure will drastically drop and the engine will be starved for lubrication. You can probably figure out what happens next.

Anyhow, I decided to take my lower pan off to check these bolts. About half way into removal, I notice some of the bolts were not stock and even a completely different size. The ones that were stock came out way too easy and had thread shavings in them. Uh oh. Great…my upper pan has stripped bolt holes and the previous owner just shoved bigger bolts in and/or overtightened others. Awesome. Well I was already invested in this so couldn’t turn back. Got the pan off and checked the upper bolts. Some good news, all were perfectly tight. I’ve heard horror stories of people finding these bolts just laying in their lower pan, so I got lucky there.

Well, after much deliberation, I decided to try and helicoil the stripped bolt holes to get the lower pan back on. Having never done that before, I was quite pleased with myself after successfully repairing 6 of the 16 holes. After patting myself on the back, I put a new gasket on the lower pan and proceed to mate it to the upper. Oh no…

It was only once I got the lower pan up there and all the bolts in finger-tight that I realized a spot on the upper pan gasket mating surface was warped. Looks like someone had whacked it with something and there was no way this was going to seal. Upon further inspection of the old gasket, it was clear the previous owner had botched this job by just squirting a bunch of RTV gasket sealer in there to keep it from hemorrhaging oil.


You can see the jacked up mating surface on the lower left. Not to mention the cracked corner top left.

Okay, no way around it. Upper pan needs replacement. I began scouring the internet for a step-by-step guide. Lots of vague information like, “oh, it’s easy, just lift the engine and pull it out,” which was less than helpful to a relative M42 n00b. The big problem is that the upper pan straddles the front sub-frame, so there’s no room to get the pan out without something moving to free up space. The e36 manual had a procedure listed, but it involved dropping the front subframe which didn’t exactly sound fun. I consulted some friends and the Reddit community (r/e30) and decided to try lifting the engine.

I rented an engine hoist ($20 a day from General Rental here in Springfield, MO) and enlisted my buddy Orin, who knows very little about cars but is always in the greatest of spirits (thanks, Big-O!), to give me a hand.

First thing was to prepare the engine to be lifted. We needed to lift it about 6 inches to get this thing out, so a few things had to be removed. Firstly, the hood, as that was kind of between the lift and the engine, y’know, this BMW is still from the glory days of front-hinged hoods. You’ll have to drain your washer fluid to remove the hose that runs from the pump to your hood for the windshield jets. After that we removed the clips holding the radiator fan shroud. You can just leave the shroud floating there, it just needs to be able to move a little so the fan doesn’t run into it when lifting the engine. The dipstick tube also needs to be removed. Mine was incredibly bent down inside the pan (damn you, previous owner!) and was quite the chore to get out. Orin had the idea to use a long screwdriver inside the tube to straighten it out, which helped greatly. Once you remove the bolt holding the tube to the engine, it should just pull out with some convincing. There should be an o-ring where the tube enters the upper pan. Mine was missing it (argh!), but yours should have it, so make sure you pull that out, too, as you’ll need to put a new one in upon reinstallation. Lastly, loosen the engine mounts. Completely remove the bolts holding the two engine mounts to the subframe, as these mounts will move enough they will completely leave their mounting locations, and those suckers are like $90 a piece, so you don’t want to rip them. I also loosened the two mounts under the transmission where it meets the driveshaft, as I figured that would move some, too, and didn’t want to rip the mounts. Those you can just loosen to the ends of their threads and leave the nuts attached.

Now we didn’t do this until after we lifted the engine, but you should also remove the power steering pump mounting brackets, as they attach directly to the upper pan. There’s a tensioner bracket and then a bolt that holds the pump itself to the pan. Once removed, just use a bungee cord wrapped around the pulley to hook it to the alternator bracket and let it hang there out of your way.

Lifting time! There’s a handy little lift point at the front of the intake manifold. Use common sense and be careful (I’ve obviously left out some parts at the beginning like make sure the car is on jack stands, have your E-brake on and chock the rear wheels, etc. etc., but I figure if you’re tackling this you’ve been under your car before and should know better). We lifted the engine until the rear of the intake manifold ran into the plastic housing at the top-rear of the engine bay just under the windshield, as that’s as far as we could take it without removing anything else.

Remove the rest of the pan upper pan bolts including the two that hold the oil sump inside the pan. All are 10mm hex bolts except for three 10mm star bolts that bolt the transmission bell housing to the upper pan. Don’t forget the two 10mm hex bolts inside the bell housing. You’ll need a skinny little wrench extension to get the wrench in there around the sway bar.

With the engine lifted this much, the upper pan should slide out pretty easy. Watch out once you break it free from the crankcase–some leftover oil was sitting in the middle of mine and poured all over me when I first pulled it off. Once free, slide the pan forward and out over the subframe.


Removing the upper pan revealed a delightfully clean crankcase.

You’ll see there’s a little rubber plug at the rear of the upper pan that keeps gunk out of the transmission bell housing. Remove that and install in the new pan. Put a new gasket on the upper side of the new upper pan using a very small bead of gasket sealant. This is also a good time to clean all of the upper pan bolts to make sure the threads are in good condition and ready to be used again. With the gasket on the upper pan, I then applied another small bead of sealant around the top side of the gasket where it mate to the crankcase. That stuff sets up fast so once you get the bead on you want to get the pan back in quickly. Carefully sneak the upper pan back in over the crank case making sure not not nick or tear the new gasket. I decided to use some blue threadlock on the upper pan bolts as they only get torqued to 89 in-lbs (about 7.4 ft-lbs) and bad things happen when they fall out, especially the bolts inside the pan. I left the sump and its two bolts off until we got the dipstick tube back in, just to give us a little more wiggle room

Now put the engine back on its mounts so its not just hanging there while you work beneath it. Re-tighten the engine mounts to 31-ft lbs. Now you can also reinstall the power steering pump. You’ll need to remove the threaded stud that holds the belt tensioning nut from the old pan and put it in the new one. Once that’s done the pump goes on pretty easily. Torque the power steering mount bolts to 16 ft-lbs. Now you can reinstall the dipstick tube. Put the new o-ring on the tube (there’s a little lip that it rests against from the bottom) and just slide it down into place and reinstall the mounting bolt at the front of the engine.


New upper pan (without sump installed) with dipstick tube.

After you reinstall the sump and gasket, also torquing to 89 in-lbs, you’re now ready to close up the bottom of the engine by reinstalling the lower pan. Same deal with the gasket…clean mating surfaces and install the new gasket. There are lots of opinions on gasket sealer, but again, I used a very small bead around the gasket on both sides. Mate the lower pan to the upper and put in a bolt in each corner to make sure it’s straight, then go ahead and get the rest of the bolts in finger tight before torquing once again to 89 in-lbs.

At this point you’re pretty much done, just put the fan shroud back on its clips, reinstall the hood and drop the car. If you haven’t done so already, put in a new oil filter and fill the engine with oil (another controversial topic among the M42 community, but her in Missouri, I feel Mobil 1 15w50 fits our climate and this engine well).

The car fired up beautifully and the oil pressure light went off after a couple of seconds, with the chattering valves quickly calming to a purr once the engine had circulated that synthetic liquid gold. While the car idled and reached operating temp, Orin and I continued to walk around the car, peeking under the engine to spot any leaks, but saw not a single drip. I’ll keep a close eye on the oil level and the garage floor, but for now, it seems that all is well and time for a drive.