Skip the auto shop - Our mechanics make house calls

Q: Extreme power loss, engine rattling.

asked by on

Hi, my post is about a 2008 BMW 523i... The car is very low mileage (43000km/26000mi). I didn't have it at the time, however the oil level was showing low and hence my father who had it borrowed at the time filled it up with one litre, just to last until it got its oil change. About one week later, the car lost power (SUPER slow acceleration, the engine light is on;), also when it revs over 2.5k rpm this weird, rattling sound can be heard. (it didn't do this at first) Since, I've had the ECU repaired as apparently it was faulty, and one injector replaced as the diagnostics were throwing these codes. These have disappeared after the fix, but the problem persists. Mechanic told me that it's likely a loose timing chain. Could adding 15W-40 instead of 5W30 create this issue? Does my (brief) description sound like that could really be it, and what needs to be repaired if it really is a loose timing chain? Does it need to be completely replaced? Thanks... :/

My car has 26000 miles.
My car has a manual transmission.

Using 15w-40 instead of 5w-30 could be the cause of your problem. Your engine has very small passages that lead to the valve train. One components in particular, hydraulic lifters, require a good flow of oil through a small passage to be able to properly function. 15/w-30 is a thicker oil than the engine is designed to use.

By using this thicker oil, oil flow through the small passages slows down. With the flow of oil slower, the lifter can’t properly operate. The result is that your intake and exahust valves will not open fully and at higher RPM’s, there is not enough flow to maintain the designed clearances between certain parts of the valve train.

The rattle you hear may be caused by this lack of oil flow, and your loss of power may be a by-product of your valves not fully opening. I would suggest a full oil change as a first step, making sure to use the oil specified by BMW. If you are still having problems, a complete engine diagnosis will be in order to determine the exact cause of the loss of power.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Car overheated and now it's shutting off. It cranks but won't start.

Hi there. If the coolant leaks out too much, the computer will see this from the coolant temperature and coolant level sensors and shut off the engine to prevent any damage to the engine. Check for the coolant leaks and...

Q: Spark plug closest to firewall /on 4.0 grand cherokee has oil on it

If you are getting oil in the back cylinder then you either have excessive oil getting into cylinder from valve seals from low oil flow in the valve cover area from too thick of oil or lack of oil changes....

Q: Loose tie rod

Hello, when you have shaking or loose feel in steering wheel that is a serious matter. The front suspension should be inspected completely. This involves lifting the vehicle up off the ground and doing a series of tests including load...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.