Hey Guys I am on step 1 of my major: do a compression test before starting... I have decided to do a compression test on a cold (no italian tune up) engine, and then another after running engine a bit (Question: I have read not to remove spark plugs from an aluminum head when hot - but most of the 355 compression tests are done with a hot engine... any points of concern? should i be replacing the spark plug as quickly as possible?) I pulled of the plugs and saw the below (arrange in order as removed from car)... Clearly the bottom 2 plugs on both sides are corroding, and the corrosion is especially bad on the left side... Any suggestions as to why? I did notice that the right side had a rubber plug on the plug leads right at the back entrance under the plug cover plate... the left side did not have that rubber plug... Any points of concern that I should look for before taking the engine out (test anything before removal)? Thanks! Image Unavailable, Please Login
The corrosion is from water getting past the spark plug wire boots on top of the plug. Likely because the gasket over the spark plug cover allows water intrusion. {the alternate explanation is driving in the rain throws water up where the slug wires enter the cover.} When you put it back together use a new gasket.
As Mitch said also sometimes oil gets in there if the rings between head and valve over are not installed perfectly Quite common
For so much rust to develop would require the car to sit unused for unreasonably long periods and/or stored in a rather wet environment and/or the plugs themselves are very old. I don't know for how long you have had this car but I sure wish her to be driven more regularly.
Just bought the car a month ago... starting a complete rebuild (major, suspension bushes, steering rack, shocks/springs, anythign else i find along the way)...
simple water intrusion into the plug area and allowed to sit/puddle from the cover/wire not well sealed. VERY common.
Also illustrates the potential value of a dab of anti seize on threads with the potential of long term storage issues...
Most plugs we use specifically say not to use antsieze and have for a long time. Besides how is antisieze on the threads going to have any impact on rust on the body of the plug from water intrusion?
Too many wives tales. Also there is so much debris on those plugs and down in the plug wells it is hard to imagine some of it did not get into the cylinders and on the valve faces making any compression or leak down test meaningless. Before any more disassembly screw in a new set of pugs, fire the engine for a minute or two, pull them back out and then do your test.
