Treating our BMW 435i to its first taste of fresh fluids

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Update by J.G. Pasterjak to the BMW 435i project car
Feb 26, 2024 | BMW, BimmerWorld, Engine Oil, Red Line Oil, Oil Change, 435i

Whenever you buy a used car, it’s safe to assume that zero maintenance has been performed. And even if some routine maintenance has been performed, getting things to whatever baseline setting you’re personally accustomed to and comfortable with is always a great idea.

This is particularly true for a car like our BMW 435i, for which regular fluid maintenance appears to be a key to longevity and reliability.

So before we did anything more than casual driving or testing, we decided it was time to freshen all the major lubricants. For the BMW, this meant engine oil, transmission fluid for the ZF 8HP automatic and differential lube.

We checked in with our friends at BimmerWorld who quickly and decisively recommended Red Line products for all these (and more) fluid exchanges. In fact, BimmerWorld will even happily put together a “new to you” kit of fluids for your specific BMW so you can get the fluid services up to date as soon as you bring it home.

Now, look, there’s lots of good oil choices out there. And while choosing the right oil seems to be as dogmatic a belief as what the fastest way to the airport is, BimmerWorld’s James Clay had some definite institutional knowledge to back up his opinions.

The turning point with me for engine oil was the mid-2000s when we were building very unique N52 engines revving over 10,000 rpm for Touring Car racing,” he tells us. “I unfortunately had a lot of data points, and we tried a barrage of oils to try to make things live. Red Line Oil was the clear winner on wear, and we doubled our engine life with this change.

I have similar stories for automatic transmissions, differentials, and cooling systems, and I've been fortunate enough to develop a relationship and learn the science behind the difference, which makes me a fairly entrenched Red Line Oil advocate.”

BimmerWorld also recommended a different weight of oil than the OEM originally did: 10W40 vs. the 5W30 that BMW specs out. BimmerWorld’s Patrick Grace summed up their recommendation thusly: “5W30 is our street recommendation and flows easily even at colder temperatures and with impatient drivers that don't wait for the engine to warm up before revving it or applying high load via a turbo making boost. 

But 10W40 is our high-performance and track recommendation to give more protection to the critical wear components of an engine like the bearings, piston rings and camshafts. Besides, you're an empathetic driver sure to warm your engine, and you live in Florida!”

Yes, Patrick, it’s warm here. And we’ll make sure to get some temperature into that 10W40 before hitting the track.

Okay, that was enough for us. We ordered their full recommended slate of lubricants for our F32 and got to work.

For most cars, fluid changes are fairly simple affairs, but BMWs being BMWs, things can get a bit more complicated in spots. So here’s a few tips we picked up during our fluid renewal adventure.

To freshen the engine oil in your N55, you’ll need 7 quarts of oil, a filter, and basic hand tools.

The drain plug is located behind a convenient flap in the underfloor protector. Yes, we have a leaking oil pan gasket. Because removing the oil pan gasket open up a whole host of “while we’re in there…” opportunities, we will continue to have a leaking oil pan gasket for a while.

We warmed the oil a few degrees and drained it into our collection bucket. We took a sample midway through the drain process to send out for analysis. Frequent oil testing is especially important on BMW engines that have a reputation for being hard on rod bearings.

The oil filter lives under this cap which sits on top of the engine. Building a little rag diaper around it and having a pan ready to receive the cap and the oil filter will reduce the amount of oil that slops around. Notice we said reduce, not eliminate. Yeah, don’t wear a nice shirt for any of these procedures.

The old filter was … okay? Not great, not horrible. Definitely ready for an oil change. No traces of anything shiny or overly gloppy, so that was nice.

The filter housing is going to hold on to a few ounces of old oil, too. Use a syringe or suction pump to remove as much as you can.

The filter cap will need to have its O-rings replaced. The filter kit should come with new O-rings, as well as a new copper washer for the drain plug.

Once you’re all buttoned up and have the new filter in place, time for 6.9 quarts of Mr. Red Line’s finest.

Checking the oil level in a BMW is, of course, needlessly complicated, but you get to look at fun graphics, so it’s not so bad, we guess. Warm the oil, then navigate to the oil checking screen located three menu levels deep in the in-car maintenance interface, and you’ll see if you did it correctly.

Now we can move back to the differential. BMW says that the diff fluid is good for the lifetime of the vehicle, so there’s every chance if you buy a one-owner used car, it’s never been changed. We’re going to fix that with some Red Line 75W90. BMW actually specs 75W85, likely as a lower-friction economy move, and that’s a reasonable choice as well. BimmerWorld likes the Red Line 75W90 for the same reasons they like the 10W40 engine oil, though, so we went with their recommendation.

You’ll need a 17mm hex key to get the drain/fill plug out of the diff. It’s just one plug, so you’ll also need something to suck out the old fluid.

Your fluid sucker needs to be able to get around the corner and down into the bottom of the diff housing. We got a giant syringe off of Amazon that came with a 120º tube adapter, but you could make something out of copper tubing or other hard line.

Once we were all sucked out, we cleaned the syringe of old fluid and used it to refill the diff. Depending on how skilled you are with the extraction, plan on a fluid change being somewhere in the 1.5-to-2-liter range.

You’ll know the diff is full when fluid comes running out of the fill hole. Second reminder to not wear a nice shirt.

Now we’ll move on to what is by far the most horrific part of the process: changing the transmission fluid. We recommend that you put on an even worse shirt and cover your garage floor with cardboard. And not the good cardboard you were saving for when company comes over, but some nasty old crap you were about to throw out.

You’ll start off by removing this protective plastic shield over the transmission. It’s held on by 8mm screws and one 10mm plastic nut.

You’ll also need to remove this heat shield to get the pan off. It’s held on by a few E10 external Torx fasteners, but it also sits really close to the exhaust, so there might not be room for a socket. We found this combination E10/E12 ratcheting wrench to come in really handy in several spots on our 435i, including this one.

Like the diff, BMW doesn’t set a service spec for the ZF8HP45 automatic. At 72,000 miles, ours still has the original pan, which means it still has the original fluid, which is not at all unusual for a one-owner car like ours.

BimmerWorld’s transmission service kit includes a new pan, which includes the integrated filter, as well as new aluminum pan bolts and a new fill plug.

You’ll need an 8mm hex to remove the fill plug, and we implore you to break this plug free before draining the fluid. Should something go awry with the fill plug after you drain the fluid, you’re screwed. Make sure you can get new fluid in before taking the old fluid out.

You’ll use a 10mm hex to remove the drain plug. The drain plug has a one-time use feature. The new pan will have a new drain plug pre-installed.

Once the fluid is drained, break the pan bolts loose by hand with a T40 Torx. These are soft aluminum bolts in a soft aluminum pan, so you want to use some touch here. Don’t go right to power tools until these are broken free.

Drop the back half of the pan to allow as much of the additional fluid to drain as possible before removing it completely. If you have a fluid drain pan with a very wide mouth, this would be the time to pat yourself on the back for your forethought.

When you finally remove the pan, ensure that you got a new filter O-ring, too. If not, you’ll want to fish it out of the filter feed hole before you try to put the new one on.

Before you install the new pan, clean off the mating surface and ensure that it’s smooth. Absolutely do not use any abrasives here. A simple solvent at the most should do the trick.

We’ll be using Red Line D6 ATF for this service. The transmission holds close to 8 liters of fluid in total, but you’ll likely only get a little more than 5 out and back in during this service.

We used our same mega-syringe to refill the transmission pan after our drain. You’ll only be able to get a couple quarts of fluid into the pan before it starts spooging out the fill hole. The fluid will need to be pumped up into the transmission to make room for the full fill.

Once the initial pan is full, hand-tighten the fill plug and start the car. Hold the brake and manually run the transmission through all the gears. This will engage each solenoid and pump fluid throughout the trans. You’ll also need an OBD interface capable of reading the transmission fluid temperature. Once that temp reaches between 104º and 122º Fahrenheit, you can do the final fill on the transmission. Do that fill with the engine running until the fluid once again runs out the fill hole.

Finally, you can replace your undercar protection, change your shirt and go for a test drive in your freshly fluided BMW.

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GTwannaB GRM+ Memberand Dork
2/26/24 9:43 p.m.

Since you are the on the maintenance subject. When it comes time to replace tires, what do you say to a GRM tire test for street performance run flat tires? Most of the tires tests lean towards 200w tires for the track. How about something less race focused?

jgrewe Dork
2/28/24 4:21 p.m.

OK, your next thing should be changing out the charge pipes. The stock plastic ones let go at the cool snap ring/clip that BMW uses on most of the hose ends.


JG Pasterjak
JG Pasterjak Production/Art Director
2/28/24 5:36 p.m.
jgrewe said:

OK, your next thing should be changing out the charge pipes. The stock plastic ones let go at the cool snap ring/clip that BMW uses on most of the hose ends.


Monday afternoon I leave for BimmerWorld to do some wrenching in advance of the SCCA Time Trials Nats even at VIR the following weekend. Charge pipes are absolutely on our list.

Oh, and I finally got around the doing the crank seal guard the other night and I'm officially declaring that BMW stands for Buy More Wrenches. Every time I work on this car I need to order more tools because everythign needs to be a very specific size to fit in the tiny, awkwardly-shaped hell hole that I need to access.

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