My Compression test, thoughts?

[n/a]

Hi, finally figured out how to set up my remote starter via the neutral back up switch, this works great and left a tag of wiring hanging for future remote starting, great tip! My old plugs were Bosch W9DC's they were all uniform whitish with heavy deposits (any thoughts?) but no oil fouling. I did my compression test with engine slightly warm, all plugs removed, throttle plate wide open, and CSV disconnected along with fuel pump and allowed two tests per cylinder and cranked 8-10 times and had the following results. Starting with number 1 (front of car) I had 170/170/165/160/160/155.  Any thoughts on these readings or any other information? Thanks again, such a great site with amazing members. Happy Holidays everyone!

[Tom]

Those readings are pretty good-within 15% of each other-which is the most important part of the test.

1971 280sl Tunis Beige Metallic (restored & enhanced)
1971 280sl Tobacco Brown (low mileage stock)
1970 280sl Deep Red (Project Car)

[A Dalton]

Fine compression....
 What kind of deposits??
 Were the insulators real white.. like chalk white??

[n/a]

I would not say chalk white but grey to white. Any thoughts?

[A Dalton]

What kind of deposits?

[n/a]

The deposits are quite crusty and white, electrodes were fairly clean, the gap was huge on these plugs, certainly bigger than .035.  what do you think?

[A Dalton]

If they have a lot of mileage on them , I would just change them and stay with the same plug..
 If they have less than 6/7 K on them, I would change them to the stock W8DCs ..
 They may have put the 9s in for oil burning , but I doubt it..

[n/a]

I think that I will stay with the good Doctor's (Dan) advice and stay with 9's since the car does use some oil and has higher mileage (129,00) I hope to check the CO in the next few days.

[rwmastel]

I always thought the gray/white crusty deposits were from running too hot or too lean in the combustion chamber.  If too lean then you may want to adjust your fuel/air mixture.  If too hot then you might want to go back to the standard and cooler W8DC plugs and see how they look after a few hundred miles.

About the burning oil, do you get smoke out the tail pipe?  How much, what color, and under what conditions?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[A Dalton]

If you like the 9s , that is fine .
 Just be aware that the actual called for plug is two heat ranges down , which is a 7.. but almost all 113 owners I know run the 8s with best results as most 113s have some mileage on the clock...
 The reason I asked about the milage on your 9s was because of your
mention of the large gaps.. if this gap is electrode wear at low mileage, than you may want to try the 8s , as rapid electrode wear is an indicator of too high a heat range..if they have many miles on them, then I would consider the gap as normal wear and stay with the 9s if it is an oil burner..
Just something to consider .. no real answer , more of a preference....

[n/a]

Good advice, thanks!  I will run the new 9's and check them in about five hundred miles.  Based upon what I see, I most likely will try 8's next to see what color I get with them.  In the meantime, I will check fuel, air CO, etc.  Thank you for your help!

James

[n/a]

You know, I just looked at my old plugs again, and they were not really all that light in color, in fact, more the color of light cardboard, or tan greyish which is good.  The deposits were heavy, but the plug age/mileage is unknown as I purchased this car a few months ago, and, as I mentioned, the gaps were huge! I stayed with new Bosche W9DC plugs with factory gaps of .035 per Dr. Benz (Dan)I have been adding 4 oz. of Mystery Oil to each tankful to benefit the FI pump and injectors.  We shall see what the next 500 miles looks like with these plugs.  Thanks!

[Benz Dr.]

White is probably too hot or lean. Grey is OK or white grey. Tan to medium brown is more to do with oil useage and black is more too rich.
I look at the electrodes and see if they're clean. If only the electrode is white/grey it's usually low voltage or rich mixture.
If you have white plugs with black specs on them DON'T DRIVE IT THAT WAY!!!!!!!  It's WAY too lean. The black spots are ( looks like pepper ) pieces of your pistons melting away.......

Standard plug is W7DC or similar acording to my Bosch aplication book. Standard gap is about .035'' This plug only works well in full compression engines of 165PSI or more, ie the Red Rockets 180 + PSI

Daniel G Caron