View Full Version : 2 Questions About Sludge

06-26-2012, 01:31 PM
in my 2007 530i -

1. how would i know if i had a sludge problem?

2. how would that problem be rectified?

06-27-2012, 12:12 AM
Sludge is either a breakdown of the base oil or contamination of the oil to such a high level that the oil thickens and begins to solidify or turn into a jelly-like consistency. It can be caused by a number of conditions, including: Severe service, Mechanical malfunctions which contaminate the oil or Use of Dino oil (non-synthetic oil). Assuming we all use name brand full synthetic oil, strike number three from the list.

Contaminants in oil are normal, but extended oil changes allow the contaminants to reach highly concentrated levels at the same time the oil additives that fight contaminants degrade due to age. The characteristics of the oil are changed and lubrication is affected.

Severe service
Short trips, stop and go driving, extended idling, extended high temperature operation, towing or other severe loads, extreme cold starting and idling, which causes the engines to either run too cold or too hot. If the engine never reaches operating temperature it wont burn off volatiles and water vapor which condense in the oil. Operating at elevated temperatures tends to thicken oil base oils (less so for synthetic).

Mechanical malfunctions Causing Contaminants to Enter Oil
Leaky fuel injectors (gasoline), malfunctioning choke mechanisms (unburnt gases), clogged or defective PCV valve (unburnt gases), excessively worn spark plugs (soot), blow-by exhaust gases from worn valves or blow-by gasoline from worn rings, and worst of all coolant from leaking gaskets.

Extended Mileage between Oil changes
Modern full synthetic oil is amazing, but the natural introduction of contaminants as the engine runs, even in a well tuned engine, begins to interfere with the additives and detergents contained in modern oil. Left long enough the oil will degrade and turn gel-like to the point that small passages in the engine designed to be lubricated no longer will be reached by oil as the sludge blocks opening. The still liquid oil that does reach other places is so contaminated that it is unable to create a lubricating barrier between moving parts.

Quoting from a Website:
Another not too often disclosed fact is that during the ILSAC or API engine tests on motor oils, the oil life is measured in HOURS, and yet only very few vehicles sold anywhere in the world have ENGINE HOUR RUN meters.

The normal motor oil recommended service frequency is specified in miles or kilometers, but the motor oil life is in hours of service.

Sure you can approximate how many miles you on average drive in how many hours, but if in your particular car you are stuck daily in stop and go traffic, you can easily average twice or even three times MORE hours of engine run time for the SAME distance traveled !
Most people in the USA spend about 500 hours in their vehicles annually while driving from 9,000 to 15,000 miles. That is an average speed of only 18 to 30 MPH !
Yet automobile industry still today equates "normal" driving with 45 MPH average, something that is almost unattainable in modern traffic unless you only drive on highways.

The longest and most severe engine oil test: "Sequence VG engine test" runs for 216 hours, and if motor oil passes this test it is suitable to be licensed under the latest API and ILSAC quality classification (API SM or ILSAC GF-4) - yet that represents MAXIMUM SAFE service interval of only 3,888 miles for someone that averages 18 MPH in typical city traffic !
But what if your MPH average is only 12 MPH ? That is ONLY 2,592 miles !

Dont think sludge can form in your Bimmer with BMWs recommended 15K oil changes using Synthetic oil?

How to know if you have sludge?
1. Examine the oil after draining from engine. Is it dark black and still pours thinly, or does it have the consistency of Elmers Glue? Does it smell like gasoline? Is it brownish in color? You probably are starting towards or already have sludge.
2. Pull the oil pan or valve covers and have a look. Sometimes sludge will be visible through the oil fill hole.

What can you do?
1. Several quick oil changes (200-500 miles between changes) with extended service oil, which typically has higher levels of detergent. This may break up some sludge, but you must get it out of the engine quickly. Usually this will have only a marginal effect.
2. Drop the pan and clean it. Pull the valve covers and clean as much sludge as you can off parts.
3. If the damage is severe enough it may be time for a rebuild/replacement or run the engine until it dies.

For older engines it is recommended that a sample of the drained oil be sent for analysis (approximately $25). This can be done every second or every third oil change. The test will analyze the oil chemistry and based on the presence of certain chemicals can indicate excessive gasoline, coolant or types of metals which can indicate wear of valves or cylinder walls. If any of these levels are excessive the first action should be searching for a cause (maybe leaking coolant gasket).

If the car is older with high miles and fixing excessively worn engine parts is not economically feasible, at a minimum reducing the miles between oil changes can potentially stretch extra life out of your ailing engine.

Moral of the story Don't let your oil get to the point where sludge forms.
If you want to keep your BMW running a long time change your oil every 5-6K miles maximum, or every 3K miles if you drive stop and go or do short trips frequently.

Get the contaminants out of your engine and she will purr for a long time.

06-27-2012, 06:26 AM
wow, that is an extremely informative post. thank you so much!

06-27-2012, 06:30 AM
how do you feel about a treatment that is supposed to clean out sludge like auto-RX?

06-27-2012, 06:33 AM
how do you feel about a treatment that is supposed to clean out sludge like auto-RX?

Auto rx is bs. I used it and cut the filter after and no difference. Waste of money

06-27-2012, 08:34 AM
I have no experience with auto-RX.

The job of cleaning out sludge is very tough.
You need to liquify the sludge (which by itself is no easy task) but you still need to provide lubrication to the engine.

In the extreme, dumping goop hand cleaner into the engine would cut sludge, but it wouldn't lubricate the engine too well, and once you cut it loose you need to remove it.

High detergent oil will reduce sludge over time, but once you begin to cut the sludge you need to get it out of the engine quickly with very quick oil changes 200-500 miles or else you will swamp the oil filter.

codog2 said he tried auto-RX and didn't see any difference. If the filter is not full of junk and the oil you drained doesn't look different than any oil change then it didn't do anything.

Once the sludge has settled onto engine walls it continuously gets cooked at very high heat. Engines with sludge run substantially hotter than a clean engine, because a large function of engine oil is carrying heat away from metal, especially the areas around the combustion chambers. The sludge prevents the oil from touching the metal walls, picking up the heat and carrying it away to the sump or oil cooler to cool.

Sludge cooked to the engine walls becomes like food spilled in the bottom of an oven - it adheres harder and gets tougher to remove.

Once the cycle begins it is difficult to reverse.

06-27-2012, 09:13 AM
ok, so i guess i will have to have the oil pan opened or the valve cover opened. question - how hard is it to do either of those things?

06-27-2012, 11:42 AM
Removing either will require replacement of a gasket. Expensive if done at a dealer.

First, do you have any indication that your engine has sludge? What are the indications?
How often was the oil changed? Do you have maintenance history?

If you have an indication that sludge is present, the best place to start is an examination under a valve cover. Due to cost a good independent BMW mechanic (Indie) is the place to start. An examination by pulling the valve cover should be identical in cost to the replacement of a leaking valve cover gasket, because after the examination they will need to replace the gasket when the valve cover is reinstalled.

On some engines the oil fill hole is positioned on the valve cover such that using a flashlight and a small mirror you can get a pretty good look inside the valve cover to see if sludge is present.

There has been talk of using a borescope (tiny camera on the end of a flexible metal sleeve with a built in light) to go into the engine to examine for sludge but I haven't heard of it being particularly successful. It is used more to examine engine block interior passages when the engine has been disassembled down to the block level.

Borescopes are also used heavily in the aviation industry to examine the fan blades (called disks) on the multiple stages of a jet engine for damage without having to disassemble the engine.

Be prepared with a plan if the examination under the valve cover indicates serious sludge exists. Ask the Indie before the valve cover is removed if they have experience in cleaning large amounts of sludge out and what the cost will be (including pulling the other valve cover and the oil pan). In addition to their cleaning they may recommend removal of other components and flushing the engine, followed by a quick oil change of maybe 200 miles.

A 2007 is certainly worth spending some money on (unless the engine has 250K plus miles already). Worth having a look if the maintenance history or other indicators suggest you may have a problem.

Many people (generally second and third owners) have been stung by BMW's recommended 15K oil change intervals. Of course the initial owner (usually a lease) never sees a problem. It is later, after 50K miles plus that the damage begins to show up.

Good luck!

06-28-2012, 08:55 AM
good advice.

i bought the car last year with only 25k miles on it, so it was either not driven very much or lots of short trips. it now has 47k miles, the last 22k miles being almost all highway.

what would be indications that i might have a sludge problem?
also, i know that when i take off the oil cap i can see small springs and engine stuff.

06-28-2012, 12:23 PM
If the engine is running fine then don't worry about what sludge may be there.

If you want to be proactive then seek out an oil that is very high in detergent (typically a full synthetic that claims extended life up to 15K miles).

You would never leave an oil in an engine for 15K miles, but the high detergent may help cut some of the sludge.

Do maybe two oil and filter changes at 2,500 to 3,000 between changes with the high detergent oil.

Then go back to your regular oil (recommend full synthetic with a number of 0W-XX) and change it depending upon your driving habits. 6K-7K miles between changes if you drive mostly highway miles. 3K-4K miles between changes if you drive mainly in stop and go traffic (average 12-15 mph for your commute).

06-28-2012, 12:56 PM
What about removing the oil filling the engine with desiel fuel and letting it soak and then draining out and adding fresh oil. I have done this before on an older engine that was full of sludge and was succesful

06-28-2012, 02:36 PM
If you have done it and felt it was successful I am curious.

What type of engine did you do it on? Gasoline or diesel?
Do you have any history of the engine after this was done? Still running strong?

Did you have to totally fill the engine to distribute it everywhere?
Wouldn't want to turn over the engine over without lubrication.

How long did you leave it in?
I have no experience with the effect of diesel fuel on gaskets but I know gasoline isn't good.