Archive for the ‘BMW’ Category

BMW M62 timing cover weep hole leaking   1 comment


We have seen this problem several times and it is usually misdiagnosed or not repaired correctly. If you have a BMW model 740i, 740il, 540i, 745i, or 745il with the 4.4 liter V8 (M62) engine, and you have a coolant leak from a small weep hole in the front timing cover, be very careful it is not misdiagnosed as a water pump or valley cover problem. What you probably have is a front timing cover to engine block coolant leak. BMW engineers were smart enough to know their design for sealing the water passage from the front timing cover to the engine block would probably not last forever, so they made provisions for a cavity to catch the coolant leak and eject it through a weep hole at the upper right corner of the timing cover. The cavity and weep whole keep the engine coolant from leaking into the engine oil that would probably lead to engine failure if not detected in time. The repair is quite labor intensive. Most manuals seem to estimate the repair time around 30 hours.  Alldata repair information service shows the timing cover remove and replace time at 30.6 hours. There are also other labor operations that should be done at the same time as the timing cover that are not included; for example, replacing the valley block cover. The cover is not re-sealable and should be replaced. Part of the labor for the cover is overlapping (removing the intake manifold), but replacing the cover itself is not included in the front cover time.

From the factory, the timing cover has just a very light sealant on the surface where the coolant passes from the cover to the engine block. BMW now offers sealing strips to better seal this surface. The sealing strips are made of metal that is laminated with a light coat of rubber-like sealant. We also use a small amount of sealant in the corners of the gaskets to ensure proper sealing. Also, great care must be taken to ensure the parts are thoroughly cleaned. At Autobahn Performance Inc. all technicians are instructed to clean parts with mineral spirits in a parts washer first, then all sealing surfaces are cleaned by sanding with 440 grit wet or dry sand paper in a figure 8 pattern. At Autobahn we rarely use surface preparation pads or discs; they are too aggressive (even the fine or soft rubber ones) and end up removing surface material and rounding off the edges of the surface. Also, with a perfectly ground flat sanding block, imperfections in the sealing surface can be easily seen and usually can be corrected or eliminated. Contrary to most technicians belief, if is not much slower to prepare the surface by hand than it is to use a die grinder and high speed surface conditioning pads (“cookie monsters”, Scotchlock pads, or green and yellow 3M surface conditioning pads). The final cleaning step is to wash the parts in hot soapy water and then dry with a hot plate and compressed air. This step removes any contaminants or oils from the surface and allows the sealant to adhere to the surface properly.

M62 weep hole at top left of timing cover. Radiator fan throws coolant upwards and all around area, making the leak appear to come from other locations. The weep hole can be seen without any dissasembly (with small flashlight). Components removed for picture.


This picture shows the cavity tthat leads to the weep hole. Cavity is vented to atmosphere (at weep hole) and is not supposed to have any fluid in it unless the primary seals have failed.



Front covers removed. 4 timing chains visible 


Autobahn Performance disassembles parts into divided bins for organization



Zymo aqueous based enzyme cleaning machine on left. Safety clean mineral spirits machine on right


BMW breather hose failure a.k.a. oil separator drainback hose   Leave a comment


We at Autobahn Performance Inc. have seen an abundance of drivability and check engine light problems for this breather hose failure. We changed three today. We usually keep 2 in inventory but will increase that number. The replacement part is inexpensive and fairly easy to replace although it is tough to see and even tougher to access. The symptom for this hose failure is usually a slightly rough idle, hesitation when accelerating at times, and rough running engine (misfires). The check engine light will usually be on with multiple codes set for misfires on some or all cylinders (codes p0301 – p0306) and random misfire (code p0300). There are usually a couple of fuel trim management codes set.
These are indicators that the fuel mixture is outside the normal controllable parameters. On a Mercedes this would almost automatically be an air mass sensor MAS or MAF sensor. We have seen lots of shops replace the MAF sensor, reset the fuel adaptation, and send this BMW customer down the road, only to have them return within a few days with the same codes set. Then the spark plugs usually get replaced — list price is currently $17.50 for each plug. The factory NGK 3199 plugs are supposed to last 100,000 miles although we recommend replacing them at 75,000 as most customers will notice an improvement in drivability and fuel mileage when done at 75,000 miles. Make sure to use the NGK plug as they seem to work and last better and longer than any other spark plug in these engines. This is opposite of what we have preached for years when we would only install BOSCH spark plugs. As a rule we try to install the same plug the vehicle left the factory with (except Bremi plugs — but that is a different story). The customer gets sent down the road again only to have the check engine light return within a few days and usually complain that the vehicle is just not running quite right. Hopefully by now the technician checks things thoroughly enough to discover the broken hose under the intake manifold. It is just barely visible with a small flashlight or a bend-a-light. The hose is easiest changed from beneath the vehicle, although it is not an easy job and brittle plastic components and other hoses must be carefully dealt with to gain access to the suspect hose. The new replacement hose may not look the same as the old one: the part has been updated, but even the updated part has been known to fail. The picture below shows one of the common high failure rate hoses on the top and its replacement on the bottom.  -> JASON ATHANAS


jason athanas 1/26/2009

Posted January 26, 2009 by jayauto in BMW