Had a mechanic friend do a compression test on my car sunday because I had previously dyno'd a little low the past weekend. Here's the results:

Cylinder #1 - 175
Cylinder #2 - 175
Cylinder #3 - 175
Cylinder #4 - 125

My friend says he's gonna add some special fluid to my oil next oil change that might help the compression. Anyone have any advice? Thanks.

 

you might need a new headgasget, maybe check the piston rings on #4 or the valves aren't seating right. Ask him what fluid specificly?

 

I'll have to find out more about that fluid.

But to add a little more, the #4 cylinder spark plug was covered in this black build up (carbon?) and i replaced they not more then a month ago when i got my valves adjusted.

 

Mike.....how does your coolant look....any slime, oil in it? If it looks clean you could probably eliminate the head gasket leak.

If I'm not mistaken, I though I read that #4 is susceptible to damage/cylinder wall scoring which would explain lower compression and a dirty plug.

When you did the valve job, was that the only plug that was nasty?

 

Coolant looks normal, nothing unusual about it.

when I had the valve job done, the spark plugs looked fine, they all had the normal wear of being used for a little over a year. I had those replaced when the valve job was done, a little over a month ago. It wasn't until I had this compression test done is when I noticed that the #4 spark plug was covered in the black crap. So now there is another new set of spark plugs in my car.

 

...I thought the coolant-headgasket connection is evident when you see white, slimey evidence in your oil...not oil in your coolant

 

If you remember it was the #4 failures that caused a big stink on '00 - '01 cars. Many of those failed (supposedly due to inadequate oiling) with an obvious noise but I would think it is possible to have the same problem with less severe symptoms. The cylinder wall scoring would lead to reduced compression and extra blow-by that would dirty the plug. Does not sound promising for your engine.

 

is 175 right for baseline? I thought I got 215-230 when I checked mine.

 

It depends, sometimes you'll get that low if the mechanic didn't unplug the injectors. The fuel basically washes down the cylinder walls and prevents the piston rings from getting a good seal. You should try the compression test again, but add a capful of oil into the cylinder before cranking to see if your numbers jump a significant amount. I think around 10 psi is normal, but more than that could point to a piston ring problem. Another option (probably what I would do at this point in time) is to get that cylinder scoped to look at the walls and see if there are any signs of scoring. I highly recommend you get that done, it would be nice to catch the problem early before you have more extensive damage occur (although I think they just replace your whole block anyway).