I'm not a really big fan of those things. I believe they use sand to lightly blast the spark plug clean. As long as you really clean it well it might be OK but becarefull and blow the spark plug off with air afterwards. Use a little bit of anti sieze on the plug threads and start by hand first. Never start with your wrench.
. In most cases I've found it's either too much fuel or oil leaking into the cylinders. I'm working on a 190SL right now and it will foul out number 3 spark plug in 10 miles. The plugs look great at first* but the longer I drive the car the worse it runs. I checked everything I could think of and found nothing. And I mean nothing wrong with fuel pump, carbs, manifolds, ignition system, fuel filter, cam timing and several other things. Nothing - nothing anywhere !
This is what I found during testing:
While doing a compression test I found that 1 and 2 were 155 PSI. Number 3 and 4 were 185 and 175 which is far higher than normal. The head is freshly rebuilt but someone put the wrong valve giudes in there and it's drinkig oil. The strange thing is, it doesn't smoke while running. The high compression is caused by all the oil leaking into the cylinders. That much oil leaking in actually caused a lean miss at cruising speed. The burning oil raised cylinder temps and could have scored the cylinder walls if gone unoticed. This engine would never run right.
After I pulled the head off I could see where the oil was running down from the exhaust valve guide, through the port and right into the cumbustion chamber. These heads are similar in design to the 113 heads so they will both burn oil that way. In the case of the 113 engine you won't get a lean miss fire due to fuel injection but you can get fouling from oil. The plug won't be wet but will be fairly dry with blackish deposits all over the place. The art of reading spark plugs is almost like reading tea leaves but it can be learned.
The main problem ( in this particular case ) is you won't see a clean plug or major build up that happens over time, because in this case, it happens in a few miles. The oddest thing about all of this is a worn out engine tends not to foul out plugs as quickly, so I must assume that compression ratio plys a part in this. In other words, a tight cylinder that's holding good compression but is being feed a steady diet of raw oil, will screw up very quicly. One that's worn out can drink all the oil you can pour into the crank case because it will leave the engine as smoke and unburned droplets. The low compression keeps the cylinder temps down and cylinder wall scoring really shouldn''t happen, or allready did a long time before ( which in this case could be weeks or even years later )
Bottom line. If you have good compression and your engine is using a lot of oil, you need to look into it. It will almost always be the cylinder head that's at fault. A worn out engine will use oil and a new rebuild shouldn't.
I also go by the way the engine smells.
If it's really rich it will burn your eyes. Turn the engine off and get way from your car if you are inside - it could kill you.
Slightly rich will simply smell like unburned fuel - it's easy to spot.
A prefectly running engine will have a slightly tangy smell almost like the smell of racing fuel as a stock cars starts up. It's a very distinctive odour. It's similar to the smell of a car with a cat converter only sweeter.
in the case of heavy oil burning - well it smells like burning oil.
The engine that burns just the right amount of oil will kind of stink. It will smell like it has old gas in the tank - not that really sweet smell like very old fuel; more like a dirty, old, skanky smell.
Engines are a sort of thing where you hear things, you see things, feel things and smell things. I can stand at the E testing station at our local operation and tell which cars will pass, and which ones won't. They all have modern systems on these cars but the ones that don't pass stink and the ones that do are sweeter than a babys breath.
When your car is dialed it will have that certain smell I described. Once you know what it smells like, you won't mistake it.
* That was a major clue. The plugs were prefectly clean after a short run because everything was working properly. The problem was inside of the engine where I couldn't see it. 10 miles later the plugs were black and fouled. If the engine was too rich, the plugs would have been black ( too rich ) on first inspection. The longer the engine ran the more time all that oil had a chance to coat the spark plugs until they quit working.
