Welcome to Tech Talk, where our resident BMW tech Nick Owen answers all your pressing BMW technical questions, frustrations, and issues. Have a question for Nick? Email him at techtalk@roundel.org. Let’s get into it.
E90 335xi Rear Suspension Creak
I have a 2008 BMW 335xi (E90, automatic) that I use for both street driving and occasional HPDE events. About two years ago (only ~2000 miles ago) I refreshed much of the rear suspension, including:
- KW V1 coilovers
- New rear shock mounts (FCP Euro E9x RSM kit)
- New bump stops and dust boots
- M3 rear suspension arms (except I retained the stock non-M rear camber arm)
- UUC 25 mm rear sway bar with polyurethane bushings
- Hotchkis adjustable rear sway bar end links
- New lower shock mounting hardware
I’m now chasing a persistent rear creaking noise. The symptoms are:
- Initially, there was creaking while entering my driveway diagonally. I found the right rear sway bar bushing bracket was loose (about a 1 mm gap to the subframe). Tightening it significantly reduced that particular noise.
- The remaining noise occurs primarily when both rear wheels cross a wide crack or expansion joint simultaneously.
- It sounds as though it comes from high in the rear of the car, possibly near the rear shock towers or trunk area.
- The noise seems to occur during both compression and rebound.
Here’s what I’ve already checked:
- Tightened the rear upper shock shaft nuts.
- Verified the lower shock mounts are tight.
- Lubricated the upper shock mount/body interface as a diagnostic test.
- Lubricated the rear spring isolators.
- Lubricated the sway bar bushings.
- Inspected the rubber suspension bushings; they still appear essentially new.
The noise could not be reproduced by slowly jacking each rear wheel individually while the car was on a QuickJack. None of the recent lubrication or tightening changed the remaining “wide crack” creak.
Has anyone seen something similar on an E90, particularly after KW coilovers or suspension upgrades? Are there known causes I should investigate before I begin removing components?
Jeff Rosedale
Well, that noise is interesting… Did it start after the suspension components were installed or did it develop over time?
My very first diagnosis step would be to disconnect the sway bar on both sides; this is easy and eliminates at least one thing.
It was definitely the rear sway bar. Disconnected both end links and rotated the sway bar, squeaking with stick-slip. A bear to clean the bushings without lowering the subframe, but was able to disconnect the left (driver’s) bracket, although I didn’t leave clearance to remove the bracket, but enough room to push and pull the bushing back and forth along the sway bar to clean it and re-lube it with Superlube/PTFE. The right side was much harder—just able to loosen it a little and get some lubricant on it. Also, the brackets may have been too tight to begin with so I was able to place a 1 mm washer between each bracket and the subframe. Also, this job needed extra-long (12”) 10mm and 12mm ratcheting wrenches to access the bracket bolts. Tightened all bolts according to the German “gütundtight” standard. Finally reset the adjustable rear end links at ride height using a jack under the right lower shock mount with the other three wheels on the ground. Test drive = no more creak.
Engine Oil and Battery Question
I currently own a 2021 X3 M40i and a 1988 325is. I am old school and once my “free” oil change ended on the X3, I started to change the oil every 5000 miles with the factory oil (0/20) and filter. My BMW Indy shop did one change using Mobil 1 5/40, but I have been my own changes since and back to the BMW’s 0/20. I have read other M40i folks using 5/30. Since I plan to keep this X3 for a long time, would using a heavier weight oil like 5/30 provide better protection? I live in California and in an area with moderate climate. I spend 90 percent of my driving time in economy mode and about 70 percent in the city streets; I only use sport mode to prove my point with other drivers who think they can cut me off.
My other question is deciding to replace my 325is’ battery; flooded or AGM. Are there any benefits with AGM and would the old charging technology impact it? Current battery almost 10 years old.
Bob
For the B58 oil, the specified weight should be disclosed under the hood. Personally, I think you should stick with the recommended weight due to the tolerances of the VANOS units and oil pressure specs. Some B58s require 5-30w, some 0w-20 and some others 0w-16. If the aftermarket has proven otherwise, it might not hurt anything to try a different weight oil…
As for the battery, an AGM battery is overkill for an e30 electrical system. I don’t think anything negative will come of using it but the earliest car I’ve ever seen use an AGM battery is from 2002.
BMW Car Preservation Tips/Guide?
I have a few BMWs that I drive one to three times a year—only in the late spring, summer, and fall when there is no danger of salt—and otherwise have them stored in a large pole barn with a concrete floor and windows that could result in direct sunlight onto the cars covered up. The vehicles are a 2011 1M that was my first garage queen, a 2005 E83 Z4 with 250,000 miles that was my first BMW daily driver for 16+ years before undergoing a new paint job and soft top replacement, and now a 2026 Z4 Handschalter that I just added.
I keep them on battery tenders and I don’t disconnect anything from the battery. I do let them sit off battery tender for about 1 to 3 weeks after a drive.
In the past, I would make sure the gas tanks were topped off before winter, but I am questioning if that is the right thing to do or if it would be better to keep a lower gasoline level to ensure that I’m changing over the gasoline with my annual driving. I’ve never added Stabil, and I am a little hesitant to put anything other than gasoline in the tank given that my cars were produced after ethanol was in existence, I don’t know if the Stabil would have more of a detrimental effect on any parts more so than just the gasoline and ethanol. I wonder what the experts think?
I’ve heard talk about tire flat spots, but after driving one of my vehicles 1 to 3 times per year over the last 10 years I’ve never had an issue with flat spots on the tires. Now the front tires on the 1M are the original 2011 tires, and the rear tires are only a year newer, but perhaps given the different sizes, maybe they are both the original tires that just happened to straddle the year end production runs. The tires are on my list of things to replace this fall or next spring, whenever I have it out again. I keep the tires filled to the suggested pressure—and really there is not much air to ever add. Are flat spots just not a problem with modern tire compounds?
I had been doing annual oil changes on my first collector car for seven years with about 500 miles put on each year. Now I’m down to about 250 miles/year and I decided to do every other year for the oil change, but I’m wondering if perhaps just timing the oil change with the brake fluid change would be appropriate enough. I haven’t changed any of the other fluids, but I do know that brake fluid in particular accumulates moisture so I am aware of the need to change that.
In terms of interior preservation, I’ve seen some people connect the seat belts on the back seats and leave them connected. My mechanic recommended that, so that is how my car with rear seats has been sitting for the last few years. I’m just wondering if that is correct or not? Any ideas on leather conditioning frequency or rubber/plastic care?
Any advice would be much appreciated. I’ve searched for some things online, but I never know what to actually believe.
Drew
I have to say I like what you’re doing so far. In my opinion, UV light is the most detrimental element to vehicle maintenance. Keeping the tires and rubber seals from constant UV exposure and extreme temperature changes (seasonal for example) is the best way to preserve their life span.
When it comes to fuel, I say keep it at or below a quarter tank. I don’t think topping off then sitting for months is the most ideal way to ensure only fuel is in the tank. But in reality, there is no way you could hurt the car by doing it another way. Generally speaking, as long as the fuel hasn’t been left to sit for years, it’s fine to sit over winter. When it comes time to drive the car again, top off with a fresh tank and the “old” fuel will dilute and burn up with the fresh tank.
If you’re using conventional synthetic engine oil, I have yet to see an issue changing it annually or every other year as long as there have not been many miles on it. I’ve serviced vehicles that sat for much longer but only went a few hundred miles and the engine oil looked really good. I’m sure there is some water content in there somewhere but for the most part, it won’t hurt the engine if you need to drive the car somewhere. It’s tough to say if the brake fluid needs to be changed every two years because it really isn’t used much with the number of miles you drive annually. Not a bad practice to change out, however.
I’ve never seen any case evidence or “standard way” of buckling in a seat belt in the buckle helps preserve its lifespan. The job of the seat belt is to prevent you and your passengers from flying forward at an undesirable rate should a rare circumstance arise. Therefore, the tension on the seat belt is the same, whether it’s buckled in or not. Interior wear can only really be judged by use over time.
