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Friday, December 19, 2014

Doug's Domain

Doug Vetter, ATP/CFI

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July 9, 2006

Power Steering Flush

Ever since I realized that BMW's recommendation for "lifetime" fluid on both the transmission and the power steering system was based more on marketing rather than engineering, I decided that I would flush the fluid at an interval BMW recommended before the advent of "free" scheduled maintenance, or around 30K miles.

In the process of creating my BMW Maintenance Schedule Worksheet, it dawned on me that it had been almost 30K miles since I replaced the steering rack and had the power steering fluid flushed. Flushing the fluid is easily a DIY project, so I bought the necessary tools and materials and did it myself. The lessons learned are in a DIY article.

Replacement of Fuel Tank Stone Guards

If you've ever looked under a BMW, you may have noticed some out-of-place plastic strips about a foot in front of each rear wheel. They are about 6" wide and extend about 1" below the bottom of the vehicle. The reason I noticed mine more lately is that they were broken almost in half and hanging down.

(Image: Stone Guard Replaced)I must admit I speculated a while about the true purpose of these things. My initial thought was they had something to do with deflecting the water stream that forms behind the front wheels in deep water, but they didn't seem positioned properly to serve that role. I quickly gave up and asked my technician for the scoop. He told me they serve two roles...

Apparently, BMW research revealed that the vast majority of flat tires occur on the rear tires because the front tires pick up whatever debris is on the road (like a stone or nail) and tend to rotate it to the vertical, pointy edge facing upward, just in time for the rear tire to run it over. The guards act as a vortex generator of sorts and create localized airflow turbulence necessary to help deflect the debris. Always the amateur aerodynamist, I'm seen my share of vortex generators and I know they really do work wonders...on airplanes...but I remain skeptical of this application.

Of course, the large horizontal surface of the guards also serve the completely legitimate and practical role of protecting the sides of the fuel tank from road debris, and it's for that reason that I decided to replace them.

The only thing that made this difficult is that I couldn't find the part numbers in the usual places, so my technician told me that I'd have to pull the parts to find them. That turned out to be very easy -- they're only held on by a 10mm bolt and what I believe to be a 6mm nut holding each part on. Incidentally, I didn't have any metric sockets below 9mm, so I used a 5/16" socket on the smaller nut and it worked fine. If you don't want to bother removing them, the part numbers on my 1998 coupe are 51 71 8 130 071 and 51 71 8 130 072 (yes, they're one digit off). The part numbers for your specific vehicle can be found in the BODYWORK->SIDE PANEL / TRIM section of realoem.com or your dealer's parts software.

Replacement of Miscellaneous Parts

While under the hood one day I noticed that the filter on the secondary air pump inlet tube (runs along the far right side of the engine bay near the top of the fender) was missing. Unfortunately, BMW only sells the entire tube, so I picked up one of those and installed it.

I also noticed that the hose connecting the intake manifold to the brake booster was a bit dried out, so I replaced that out of concern for a vacuum leak that would affect both engine performance and brake booster operation. It only cost a couple of bucks including two new clamps, so that was a no-brainer.

And, while I was looking at the brake booster hose, I got a close-up look at the flexible intake pipe that connects the throttle body to the mass airflow sensor. Cracks in the material were apparent adjacent to the large band clamps, so I figured I'd replace that as well. At $35, this was the most expensive of the miscellaneous parts, but necessary to prevent an intake leak and the many problems that would result from one.

Prep for A/C System Fix

While having some fun during a spirited drive, I had the windows open to vent the interior and heard a strange whining noise coming from the engine bay that varied with engine speed and was most noticeable above 4000 RPM. I initially thought it might have been the power steering pump given that I'd just worked on the system, but on instinct I turned off the A/C compressor and the noise went away. Upon coming to a stop, I heard the usual rattling noises coming from the compressor...only this time they were louder. I resolved at that point to replace the compressor. Another big bill, that's for sure, but it's all part of the restoration process.

Two different OEMs produce compressors for the E36 and there's no way to tell which one is appropriate for the vehicle without looking at the unit. Unfortunately, the information I needed was in a hard-to-reach spot (on the bottom near the rear of the compressor body), so my technician offered to put the car up on the lift. Within 30 seconds we found "Denzo" on the unit and asked the parts department to put one on order. Thanks again to my tech for taking time out of his ridiculously busy schedule to make all our lives easier come installation day at the end of the month.

Total Mileage: 129990, Parts: $92, Labor: $0, Total: $98, Labor Savings: $150

July 25, 2006

Auxiliary Cooling Fan Troubleshooting

After coming home from the dropzone last weekend, I decided to wash the bugs off the front end of the E46 before putting her to bed. While I was cleaning the grills I noticed the aux cooling fan started up, smoothly spooled up to a modest RPM and then -- presumably as the coolant temperature dropped -- ramped back down just as smoothly and turned off. At that point it dawned on me that I could not remember when I last heard the aux cooling fan operate on the E36. Since I'd heard it's supposed to run when the A/C is on and it most certainly has not been running (at least when I've been looking), this got me to thinking -- maybe it's broken and has been for a long time.

(Image: Aux Fan Block Diagram)I got up early today to enjoy the uncharacteristically crisp morning air and do a bit of troubleshooting. I reviewed the Bentley manual, which revealed the troubleshooting procedure. NOTE: the wiring color code in the troubleshooting section is WRONG, though fortunately the schematics in the rear of the manual are correct. I had to go through this procedure twice to get it right because of this discrepancy. Lesson learned? When working on BMW's and looking for a ground, think dirt (yes, "brown"). Anyway, here's the procedure:

  1. Disconnect the connector from the coolant temperature sensor (located at the top right of the radiator). Insert three pieces of wire (I used some solid copper from a piece of ethernet cable) into each of the three pins of that connector, and, with the ignition key in the "ON" position but the engine stopped, test for power. The center pin is ground, but to elminate the ground as a possible fault, I used a frame ground. I found 12 volts at pin 1 and 3 (the outer two pins).
  2. I then bridged the center pin of the coolant temperature sensor (brown wire, or ground) first to pin 1 and then to pin 2 to simulate a high coolant temperature and turn on the fan manually. As the aux fan on the E36 is a simple two speed unit, closing either circuit sends power to low and high speed relays located in the fuse box. The relays are needed to deal with the high power (30A) circuit required to power the fan.
  3. I pulled both the low and high speed relays and checked for power on pins 30 and 86 (these numbers are imprinted on the relay contact blades). I found 12 volts on both pins of the low speed relay but only on one pin of the high speed relay. There should be power on both pins on the high voltage relay, but the Bentley has been wrong before. Not sure if this is significant.

Fortunately, as I intermittently activated each circuit, the fan ran in low and high speed modes. That meant the fan and much of its control circuitry was okay -- and good thing too....the aux fan is $670(!) according to realoem.com. This test confirmed what my technician told me earlier, the fan is almost perfectly quiet running in low speed. And in fact it's not terribly loud running in high speed either. If you look at aerodynamic design of the blades this is no surprise -- they're designed with swept airfoils to negate the air turbulence that we hear as noise. This means it's likely that I wouldn't hear it over the engine or the engine driven fan -- I'd have to look at it instead.

Why did I go on this little detour to test the aux cooling fan when I was about to replace the A/C compressor? The A/C system needs a reasonable airflow through the condenser (a radiator-like device mated to the front of the engine coolant radiator) to dissipate the heat generated during the compression phase of the vapor cycle. If airflow is insufficient, the condenser fails to do its job and the pressure does not bleed down as much as it should. The compressor must then work against this higher-than-normal pressure to get its job done. This can cause the valves in the compressor to chatter -- and that's exactly what my compressor has been doing for at LEAST three or four years. Could the aux fan or one of its control circuits been broken that long? Certainly.

The BMW docs indicate that on the six-cylinder E36, three things turn on the aux fan:

  1. A request from the IKHA control panel / module
  2. High coolant temperature
  3. High refrigerant pressure

The point to bring home here is that the fan does not automatically turn on when the A/C "snowflake" button is pushed, nor will it run, apparently, unless there is insufficient airflow over the condenser. Since I drive mostly on the highway and the speed helps maintain reasonable coolant temperatures as well as refrigerant pressures without the need for even the engine driven fan, it's no surprise I haven't heard (or seen) the aux fan run lately.

Toys for the Birthday Boy

This morning I reached the mighty old age of 37. This means two things. First, I'll have to increase the minimum age on female prospects to 21 to remain "respectable" (or whatever I was when I started dating). :-) Second, it means I'm fully justified in buying some additional toys -- in this case, some essential tools I'll need to work on the cars and the airplane.

I just went to a local tool house called Eppy's. They have a great selection of reasonably-priced tools including SK. I used to work with hand tools every day in my previous life as an electrician, so I know how to abuse a tool. We beat on SK ratchet sets and they worked like the proverbial Timex, so choosing SK was a no-brainer.

This past weekend I wound up buying two torque wrenches (3/8" and 1/2" drive) with full metal handles and pivoting heads for getting into those odd places, a range of Torx sockets for the interior, a shallow 36mm socket for the oil filter cannister, one impact socket for the wheel studs (yes, I'm planning a full suite of air tools, too), and a giant 32mm wrench essential to remove the engine-driven fan. This ran about $600, and I'm not done yet, but I figure if I can get my toolset up to snuff quickly enough I can do the brakes on my own this time and nearly offset that amount in labor savings.

Truth be told, I considered going "high end" with Snap-On, at least for the torque wrenches, since I have worked with their stuff before and like it, but I don't intend to use these tools every day and I felt my tool dollars would be better spent on a wide range of tools rather than one or two items. Plus the local Snap-On rep never called me back. Way to push product, dude.

Tools and Equipment: $600, Mileage: 130552.

July 28, 2006

More Aux Fan Fun

I took the car in today for its appointment to have the A/C Compressor and Dryer replaced. I told my technician of my recent success in testing the fan and thought the refrigerant pressure switch was the culprit. After all, by sending voltage to the coils of the low and high speed relays I verified the relays themselves as well as the fan were in good shape, but the fan was still not running after several minutes at idle with the compressor running. Something was still wrong with the system.

He suggested that it's very rare to replace a compressor and they usually fail only because they've been run low on oil. That certainly wasn't the case here, but we couldn't ignore the compressor chattering. He reiterated that the compressor can get noisy if its working at higher-than-normal pressures and he'd need to spend some time troubleshooting the problem before he would feel comfortable changing the compressor and dryer outright. I agreed to leave the car with him for the day, and I got to drive an X3 around some sharp corners and scare myself. No, it's not a Coupe by any stretch.

Anyway, later in the day my technician let me know the culprit turned out to be the low speed relay after all. With the fan disabled, refrigerant gauges on the system showed the high pressure side peaking at nearly 350 PSI, while a typical maximum on this 90 degree F day was more like 250 PSI, simply due to a lack of airflow over the condensor. He didn't have the relay in stock so he ordered one and rigged the old relay contacts to remain closed at all times so the fan ran in normal speed mode continuously while the A/C was on -- not a perfect solution, but sufficient to confirm that the compressor itself appeared undamaged. This fix eliminated 90% of the noise as the running pressure dropped dramatically.

The remaining 10% of the noise appeared to come from the belt and idler pulley. He removed the 1-month-old A/C belt to find it in pretty bad shape -- apparently the extra load on the compressor had taken its toll on the belt. Upon closer inspection he then saw grease leaking from the A/C belt idler pulley (the only pulley we didn't replace during the cooling system overhaul). Naturally, he installed a new pulley before installing a new belt and later remarked to me that the compressor is now "quiet as a mouse".

The good news is that these fixes have eliminated the noise from the compressor and repaired some critical components of the A/C and cooling systems. The bad news is I have no idea how much damage I've done to the compressor over the years it's been running like that. For now, it seems, I'll avoid the cost of a compressor, but I'm still somewhat concerned about how long it will last. And I'm also concerned about the dryer, since those are known to fail and clog up the expansion valve with dessicant. I figure I've just put off the inevitable, but that's okay with me. I have several more pressing things to spend money on.

Total Mileage: 130764, Labor $255, Parts $75, Total $352.