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A year ago, I ran into an intractable problem with my GL. After wasting $1300 and countless hours, I finally traced the problem to carbon on the undersides of the intake valves.
Re-reading my owner's manual, which I do when unwinding for the evening, I noticed this on page 564:
Hot dang. Note that MB points at other "engine manufacturers".
You get a little oil leaking down the intake valve stem seals, you go on some short trips in the dead of winter, you get hunks of carbon on the intake valves, your Bosch ME9.7 ECU is completely incapable of reporting what has gone wrong ... and you end up replacing the motor.
It's interesting that they actually took the time to write about that when most manufacturers would try to keep that a secret. Once, when "unwinding" and reading my old '97 BMW's manual, I came across a section that went into great detail about WHY the auto HVAC does what it does and why directs warm air some places and cool air other places. The short of it was that it is more comfortable to have warm feet and a cool head than the other way around. Makes sense. I just thought it was quite unusual (but very nice of them!) for a car's owner's manual to go into such great detail as the how and why.
If you're looking to try some additives... Yamaha's Ring Free is pretty amazing stuff. Mercury makes a product called Quickleen that is excellent, too. Supposedly Techron's version of this stuff (at Autozone) is very similar but less expensive. I have no experience using Techron but I do have quite a bit with the other two and have had REAL success eliminating running issues with those things. Double dose it. My experience is with marine engines, but they still suck/bang/blow just like a car engine
Yes, I find the weighty tome most relaxing. I only got to page 564 because I was reading from back to front.
The European manuals are fun. I recall the 1971 Volvo manual similarly waxing poetic about the nobility of warm feet and cool face. In this case, you can just hear the engineering department adamant about Informing the Public, unaware the factoid would be buried at the end of the manual. The rest of the manual is maddening in its Covering-Corporate's-[donkey]; I sat with a pdf editor to try to clean out all the unnecessary stuff and realized it would be quicker just to copy the pages that were actually useful. Most of the manual is like the main display warning you that the passenger side air bag is off. OK! I recall this from working with engineers: They would go down what-if rabbit holes, which I think for them was the thrill of the chase.
Aye, there are fuel additives out there, but it can be a bear to figure out what they actually have going on inside the bottle. Plain old naphtha seems to do the trick. Most of the additives contain it. Techron is polyetheramine. Supposedly it is the boss. By studying the Safety Data Sheets, I was able to divine that two Gumout products appear to be 30% PEA. One is cheap at Autozone: Gumout Regane Complete, $7.49 / 12oz. Gumout All In One is about 50% more costly for what appears to be the same fraction of PEA.
I am puzzled about the engine design leading to carboned intake valves. In this case it was possibly due to marginal quality gas, but more like due to chronic short trips in sub freezing temperatures - coupled with oil leakage down the intake valve seals. Port fuel injection is probably worse in this regard; the fuel spray cools the valve and also ensures the fuel spray is as cool as possible when entering the cylinder. It would be swell if the spray could be directed at a hot spot; ideally it would be vapor when it entered the cylinder.
I cleaned the carbon and added Liqui Moly hydraulic lifter quiet to the oil, which I believe swells rubber seals (the oil consumption dropped considerably) and am leery of short trips. And I toss a bottle of Regane Complete in every other tank or so.
This is a recently developing problem with direct fuel injection where there is no gasoline ever in the intake manifold. This of course coupled with "positive crankcase ventilation" which has been required since the 1960s and still runs those byproducts to the intake manifold.. My friend's tin can RAV4 has dual injectors, one in manifold, one direct to cylinder to combat this.
12-02-2022, 06:56 PM
