Carbon Build Up Deposit
Senior Member
Joined: Jul 2014
Posts: 422
Likes: 61
From: South East US.
2015 GLK350
Direct injection engines spray the fuel directly into the cylinder unlike older injection that sprayed upstream of the valves. This means that the intake valves don't get "washed" by the fuel spray and some of the older direct injection engines developed carbon buildup on the intake valves. The buildup is bad because it reduces intake flow and reduces power, efficiency.
I did a bit of reading about this a few months ago and it seems to not be a problem with our engines however I think some earlier BMWs had some trouble.
I did a bit of reading about this a few months ago and it seems to not be a problem with our engines however I think some earlier BMWs had some trouble.
Thread Starter
Member
Joined: Jun 2018
Posts: 90
Likes: 9
GLK350
Direct injection engines spray the fuel directly into the cylinder unlike older injection that sprayed upstream of the valves. This means that the intake valves don't get "washed" by the fuel spray and some of the older direct injection engines developed carbon buildup on the intake valves. The buildup is bad because it reduces intake flow and reduces power, efficiency.
I did a bit of reading about this a few months ago and it seems to not be a problem with our engines however I think some earlier BMWs had some trouble.
I did a bit of reading about this a few months ago and it seems to not be a problem with our engines however I think some earlier BMWs had some trouble.
That being said, is there anything to look out for with these GLKs? I know the earlier year models were known for the balancer issue. Otherwise, the GLK sounds like its built like a tank
Junior Member
Joined: Aug 2017
Posts: 66
Likes: 5
2013 GLK350 4-Matic
Didn't even think of the Direct Injection being downstream from the valves. Makes sense what you said though. I guess the Techron will at least keep the injectors clean and maybe the combustion chamber possibly.
Super Member
Joined: Aug 2011
Posts: 861
Likes: 38
From: Philly area
350 GLK, C280
The build up on valves also causes the valve not to contact the head so that they do not cool, even though they don't leak. Results in burnt valves in the BMW's. Other problems with the basic engine is the dual manifold cross over valve actuators and the anti-lock brakes/stability control pumps and valve system after 100,000 miles
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MBWorld Fanatic!
Joined: Jan 2009
Posts: 2,780
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From: Northern NJ
GLK 350 / Porsche 993
Can somebody educate me a bit.
Pre-DFI or DFI, there should be carbon build up on the exhaust valves.
Why having build up on the intake valves is such a big issue and on the exhaust valves is not.
Pre-DFI or DFI, there should be carbon build up on the exhaust valves.
Why having build up on the intake valves is such a big issue and on the exhaust valves is not.
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Super Member
Joined: Aug 2011
Posts: 861
Likes: 38
From: Philly area
350 GLK, C280
Exhaust valves are generally larger and have more contact surface area for cooling. Burnt valves have been with us since the beginning of the internal combustion engine. Lean carburetors and retarded ignitions were the primary cause of valve burning before all the electronics. Now with knock sensors and perfect 14.7:1 fuel ratios set with direct injection, burnt valves should be a thing of the past, however, that was seen to be not the case. The search for efficiency and fuel ratio programming by the manufacturer may not be as an exact science as some manufacturers thought, so a little too rich for acceleration adds deposits, a little too lean for standard running adds heat, a tweak on the timing, who knows, and the valve doesn't cool so a little melts.
I believe the BMW problem is in the design of the head. Inlet valve guides are lubricated from the heads with engine oil. Since the valve stem is open to the combustion chamber during intake, a DI engine doesn't wash the valve stem as in Non DI engines, so sticking may occur from burnt oil deposits as the valve moves up and down through the guides. Anyone who had a VW Rabit knows that leaking valve guides have been a big problem since the '70's in many German cars. American cars and Japanese cars have all had problems with valve guide seals. That little cloud of white smoke that appears after idling at a stop light then goes away, is a sure sign of bad seals. Again, a sticking valve that doesn't make good contact to the head when closed will not cool and will eventually burn.
On this board, there doesn't seem to be any talk about valve problems, so MB must have done something right.
I believe the BMW problem is in the design of the head. Inlet valve guides are lubricated from the heads with engine oil. Since the valve stem is open to the combustion chamber during intake, a DI engine doesn't wash the valve stem as in Non DI engines, so sticking may occur from burnt oil deposits as the valve moves up and down through the guides. Anyone who had a VW Rabit knows that leaking valve guides have been a big problem since the '70's in many German cars. American cars and Japanese cars have all had problems with valve guide seals. That little cloud of white smoke that appears after idling at a stop light then goes away, is a sure sign of bad seals. Again, a sticking valve that doesn't make good contact to the head when closed will not cool and will eventually burn.
On this board, there doesn't seem to be any talk about valve problems, so MB must have done something right.
Junior Member
Joined: Apr 2018
Posts: 30
Likes: 8
2011 GLK350
Compare that to intake valves, which are cooled significantly during the intake portion of the combustion cycle, aren't heated during the exhaust cycle, they are heated a bit less than the exhaust valves during the combustion and compression stages (less exposed area in the cylinder), and don't hold as much heat due to their smaller volume. They never get hot enough to burn off any deposits that accumulate.
Last edited by CarbonKevinYWG; Jul 11, 2018 at 01:20 PM. Reason: clarification
