Spark plugs fouled BADLY!!! HELP!! - PeachParts Mercedes-Benz Forum

mike690003 · #1 07-10-2003, 05:58 PM

Hello Board, I have a 1987 300E, I pulled the spark plugs today and # 1,2,3,6 were covered with a hard crusty build up. I think have 2 problems:

1. My car is running rich, It could be "carbon bulid up"??. I've posted this a few times,.

2. My car's oil is too thin(I live in Miami,FL and I run 10w-30) and is leaking past my valve stem seals. I think that I will have to switch to 20w-50. I noticed a little oil on the threads of the spark plugs.

What could that hard crusty build up on my spark plugs be??

Oil or running rich OR BOTH??

HELP!!

bjcsc · #2 07-10-2003, 06:50 PM

I'm no expert plug reader, but there's a link that might help below.

Reading Spark Plugs

Duke2.6 · #3 07-10-2003, 06:58 PM

What is the make and model of spark plug?

How long were they installed?

Are they the proper heat range (Bosch "9")?

What is your measured rate of oil consumption?

How about driving habits. Do you do a lot of short trips - say less than five miles?

What do you mean by fouled? Tan colored oil ash deposit buildup on the insulators is normal if the engine has fairly high oil consumption, but may be due to too cold a plug. Dry black carbon deposits could be an indication of a rich mixture or too cold a plug. Wet black deposit buildup could be an indication of oil consumption or too cold a plug.

Any of these indications could also be a result of short trip driving.

Duke

mike690003 · #4 07-10-2003, 07:18 PM

I have the standard bosch coppers H9DC

Would you say that the 10w-30 oil is too thin and leaving past my valve guides?

I drive about 100miles a week and I add about 1/2 quart a month, so its about 1/2 quart every 400miles, in city driving. I rarely drive highway.

Will 20w-50 oil stop the fouling( by being too thick to past through the valve guides)??

The H9DC bosch comes pre gapped, should I adjust the gaps higher than how they come??

kip Foss · #5 07-10-2003, 09:13 PM

Changing the viscosity of your oil will not stop oil from getting past your valve seals. Chances are good that your seals are gone. Going to the next hotter plug heat range will help a bit but will not solve the problem over the long term.

sixto · #6 07-10-2003, 09:20 PM

I don't know if 10W-30 is too thin but I'm pretty sure it's not on MB's approved oil list for use in Miami. Even if the plugs weren't fouled I'd switch to a -40 or -50 oil ASAP. I can't read oil labels and I avoid oil threads so I don't know if 0W-40 and 15W-50 synthetics are thinner or thicker (more or less viscous?) than 10W-30. 10W-30's Honda oil

More than a quart in 1000 miles is cause for concern in my book. Again, even if the plugs weren't fouled I'd look into doing something about it.

Any chance of a picture of your plugs?

I think at the point that you're running rich enough to have chunks on the plugs you're probably leaving a trail of smoke that would shame a Diesel.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Duke2.6 · #7 07-10-2003, 09:36 PM

For Miami I would recommend 20W-50 mineral oil year round, but it probably won't put a big dent in your oil consumption. If you're only driving 100 miles per week, you could just change it once per year. Consider new valve seals. A decent independent shop should do the job for about $300.

It sounds like short trips and relatively high oil consumption may be resulting in some deposit buildup, but unless the engine misfires, it's not a big deal. The Bosch H9DC is THE correct plug and they should be pregapped at .032", which is Mercedes' recommendation, but plug gap should always be checked prior to installation.

Before I refreshed the cylinder head on my Cosworth Vega last year it was consuming a quart of oil every 100 miles, but the plugs (HR9DC - same as the 103 engine except for resistors) did not foul out though they did build up a lot of oil ash deposits on the insulators.

The new guides and seals reduced oil consumption to about a quart every 5000.

Duke

mike690003 · #8 07-11-2003, 09:11 PM

Here are a picture of the plugs, I hope they are clear enough. I am very sorry for the pics guys I am in need of a new camera. Well, what dou you guys suspect my problem could be?

The plugs are black and have a crusty deposit on the electrode.

psfred · #9 07-11-2003, 10:27 PM

You are running too rich, and need to find out why. Can be a bad O2 sensor (surely fouled, too, by now) or a missadjusted mixture, ignition problems, a bad EHA, and so forth. No way to tell without testing.

You can check with a multimeter with a duty cycle setting (Sears has a good one for about $30) -- duty cycle signal is between sockets #2 and #3 on the X11 diagnostic socket on the fender by the coil -- it's the one with a cap screwed down on it. Should read 70%, I think with key on and engine off, going to about 50% with engine hot and moving around a bit. Steady 50% running all the time is a bad O2 sensor, very high or very low is mixture not being controlled.

You also need to check the EHA current, requires a cricuit completing milliammeter that can read plus or minus 20 mA easily. Digital ones are a bit steep, but an old analog will work fine.

If this is over you head, check out the very good DIY article in the DIY section from Steve Brotherton, or take it to a mechanic, you need to get this fixed.

The hard crusty stuff is oil burning ash -- for sure you have leaking seals. Synthetic oils leave less ash, so that may help, and they are also higher viscosity hot. I use 15W-50 Mobil 1, but any full synthetic of similar viscosity will work. I would not use 10W anything in Miami, MUCH too hot in the summer!

Peter

mike690003 · #10 07-11-2003, 10:43 PM

Thank you for the valuable information.

I have a question: Does running too rich thin my oil(10w-30),and in turn make my car burn too much oil, and in turn foul my plugs??

Could I use an old fashioned analog multimeter to adjust my cars mixture or do I have to buy a digital one??

I have a BRAND NEW analog multimeter and I'm ready to use it.

pesuazo · #11 07-11-2003, 10:43 PM

I second the opinion about your valve stem seals being in bad shape.
But replacement may not be necessary. I had the same problem.
I switched to Castrol High mileage or Valvoline Max-Life, I only use 20W-50.
Before the switch I used about 1 quart of oil per 500 to 750 miles; sparkplugs needed cleaning at every oil change too (dark crust).
After 4 oil changes (at 3000 miles intervals) now the car uses 1 quart every 2500-3000 miles!!!, and the sparkplugs look clean.
This is not a snake oil comercial. I do not work for either oil company.
I am just sharing my experience with these oils.
I believe another contributor in this forum had a great experience with them.
This may not work for you, but is worth a try.

mike690003 · #12 07-11-2003, 11:04 PM

I doubted my seals are worn out also. I had to buy a "new" used from a 1989 300E(my sister blew the original engine's head going to Key West). The engine was in great condition and the car had 86,xxx on the odometer. It was rear-ended really bad, but still drove perfectly. I have put about 10,000 miles in the 4 years I've had the engine installed( I dont drive a lot). I was told by an "indie" to use 10w-30. Call me nuts, but I change my oil every 2 months(800miles) !!!!

I am glad this forum has showed me the PROPER oil weight to use in my car (20w-50). I will change my oil TOMORROW and report the results of my oil consumption.
in another thread.

Stay tuned..I could also be a success story

psfred · #13 07-11-2003, 11:30 PM

Put a whole bottle of Techron or RedLine injector cleaner in the next two tanks of gas, too -- if #4 and #5 looked normal, you either have dirty injectors or a leak at the injector seal on the two clean ones. I've been told leaks are unlikely, but hey.....

Peter

mike690003 · #14 07-11-2003, 11:41 PM

The #4 and #5 were not as bad, but they were fouled. I recently put about 7 bottles of the "STP" fuel injector cleaner in my car on an almost empty tank. I drove around until it was really near empty. Was that a good idea?? I mean that was a super duper concentrated mixture.

haasman · #15 07-12-2003, 03:03 AM

I think 7 bottles in an almost empty tank is way too much. The idea is to clean the injector pintels not ruin them. The cleaners in these bottles are meant to be mixed with fuel. The fuel actually provides a lubricating value.

I used Valvoline Max-Life in the 300E. It definitely improved the oil consumption: 1,000 miles per quart to about 2,200 miles. When I stop using it the oil consumption slowly increases. Search using: Haasman + Valvoline Max-Life.

I have often found that going slow, being methodical and analytical with determining what is wrong with a Mercedes pays off in more ways than one.

A lot of people spend a lot of money throwing parts at their cars to repair problems, when often simple adjustments after careful analysis is all that is needed. Some think that since it is a Mercede$ that the repairs $hould al$o co$t a lot .... not necessarily in my experience.

Follow the advice you just received: Check your mixture.

Keep us posted,

Haasman

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