saf@bonnie.UUCP (Steve Falco) (11/22/85)
Sorry to those of you who saw this twice - I inadvertently sent it to net.auto by mistake... ----------------------------------------------------------------------- My '79 Chevy 305 V-8 recently started running rough under light loads - sort of a miss... I pulled the plugs to do a compression check and found two plugs had some white, brittle crud on them. One was so bad that the stuff had almost filled the area between the ceramic and the shell - it had also gotten into the gap. Ah ha! Here is the miss. I cleaned the plugs (which have under 10k miles on them - supposedly ok for the HEI ignition) and sure enough the miss went away. What is this white crud and what causes it? Oil fouling is usually black; could this be a deposit from BURNED oil? How about gas residue? (The car burns unleaded premium.) A friend suggested bad wires - this would cause a slight miss leading to a buildup of unburnt gas on the plugs. I am planning to change cap, rotor, and wires since the engine now has 50k miles on it. BTW, the compression was between 170 and 180 psi on all cylinders; does anyone know what the spec is? The shop manual doesn't seem to have it!! Steve Falco
tmorris@convex.UUCP (11/25/85)
Which two plugs were they ? Cyls. 7&8 often do this on small blocks when the valve guide oil seals go out . Due to the tilt of the engine in the chassis (about 7 degrees in most vehicles ) , the oil in the valve covers has to run past the valve guides to get to the drain hole to the crankcase . If the valve guide seals are gone (they usually crack and break off ),then oil can be drawn in on the intake stroke and burned . Due to the path it takes in the combustion chamber (ie in with the fuel , across the plug gap due to swirl ) it tends to build up on the plug. Why is it white instead of black ? Because it is a very small amount of oil , and it is being concentrated on the hottest part of the combustion chamber . The result is not oil residue per se , but the ash left from burning the oil ADDITIVES at high temperatures . Another unpleasant result is pinging when the engine gets hot , as the deposits retain enough heat to pre-ignite the mixture before the spark is applied . The deposits also form on the faces of the valves , and are most resistant to any combustion chamber cleaner . Head removal is usually the only method of cleaning at the advanced stage .Prior to that , try changing the guide seals (can be done without removing the heads) and a fresh set of plugs. tmorris@convex ,disclaim,disclaim!
bcking@inmet.UUCP (11/27/85)
*** reface this slime with your message *** It sounds like ash deposits formed by burning oil additives. If the car has been burning oil recently, you may want to do one or more of the following: - Stop using an oil additive, if you're currently using one. - Try a different brand of oil; one with less additives in it. If the car's burning oil it's probably getting to the combustion chamber via worn valve guides (this is a chronic problem with small block Chevys). A valve guide job is in order if you're real fanatical, but since small blocks don't die (they just fade away) you may want to wait the 50k miles or so until the engine really needs it... Probably the best thing to do is just put in new plugs and see if it happens again. About the compression check- don't worry too much about that either. Compression readings can fluctuate wildly with changes in ambient temperature and humidity. As long as they're all within 10% of one another things should be O.K. If you're still concerned you might want to take the car to a good tuneup shop for a leakdown test. R.M. Mottola Cyborg Corp. Newton, MA. (Reply posted for me by a friend, but not for long)
saf@bonnie.UUCP (Steve Falco) (12/03/85)
I had to bring my Chevy to the dealer for a rear brake recall (the one where the wheel cylinder falls out tangling up the brake shoes and causing a loss of brake fluid). I asked him about the white, crusty deposits I had on two adjacent spark plugs in my 305 V8. (Cylinders 6 and 8.) He said "No problem, sounds like antifreeze is getting into the cylinders. Probably just a blown gasket or a crack somewhere." NICE!! A few people have responded to my first posting saying that the deposits could be caused by oil additives. I don't use any special additives but of course there are some additives in any oil. Can anyone offer a way to determine whether the deposits come from oil or antifreeze? Pulling the heads is a bear! BTW, the engine uses a quart of oil in 1000 miles. This can go up to a quart in 250 miles when driven hard. I suspect the oil consumption is at the valve stems since compression was OK - wouldn't they all wear evenly causing deposits on all plugs rather than just two? Steve Falco
seifert@hammer.UUCP (Snoopy) (12/05/85)
In article <643@bonnie.UUCP> saf@bonnie.UUCP (Steve Falco) writes: >I asked him about the white, crusty deposits I had on two adjacent >spark plugs in my 305 V8. (Cylinders 6 and 8.) He said "No problem, >sounds like antifreeze is getting into the cylinders. Probably just >a blown gasket or a crack somewhere." NICE!! > >Can anyone offer a way to determine whether the deposits come from oil >or antifreeze? Pulling the heads is a bear! Especially if they're cast iron instead of alloy. Are you losing coolant? Is there steam (white) from the exhaust? Snoopy tektronix!tekecs!doghouse.TEK!snoopy
dennis@vrdxhq.UUCP (R. Dennis Gibbs) (12/05/85)
In article <643@bonnie.UUCP>, saf@bonnie.UUCP (Steve Falco) writes: > > I asked him about the white, crusty deposits I had on two adjacent > spark plugs in my 305 V8. (Cylinders 6 and 8.) He said "No problem, > sounds like antifreeze is getting into the cylinders. Probably just > a blown gasket or a crack somewhere." NICE!! > > Can anyone offer a way to determine whether the deposits come from oil > or antifreeze? Pulling the heads is a bear! BTW, the engine uses a > quart of oil in 1000 miles. This can go up to a quart in 250 miles when > driven hard. I suspect the oil consumption is at the valve stems since > compression was OK - wouldn't they all wear evenly causing deposits on > all plugs rather than just two? > > Steve Falco You might want to have your engine oil and engine coolant analysed, in an engine oil analysis, they indicate any (and how much) coolant is contained in the oil. Also, the antifreeze analysis can tell if there are exhaust contaminants in the coolant. The cost for both analyses would probably be around $40, a lot cheaper than pulling the head. Usually if you have a cracked head or blown gasket, it is easily detected in this manner. Dennis Gibbs
marauder@fluke.UUCP (Bill Landsborough) (12/05/85)
In article <643@bonnie.UUCP> saf@bonnie.UUCP (Steve Falco) writes: >I had to bring my Chevy to the dealer for a rear brake recall (the one >where the wheel cylinder falls out tangling up the brake shoes and >causing a loss of brake fluid). > >I asked him about the white, crusty deposits I had on two adjacent >spark plugs in my 305 V8. (Cylinders 6 and 8.) He said "No problem, >sounds like antifreeze is getting into the cylinders. Probably just >a blown gasket or a crack somewhere." NICE!! > >A few people have responded to my first posting saying that the deposits >could be caused by oil additives. I don't use any special additives >but of course there are some additives in any oil. > >Can anyone offer a way to determine whether the deposits come from oil >or antifreeze? Pulling the heads is a bear! I would suggest if you have a good radiator to have it pressure checked. They remove the antifreeze and pressurize the radiator and let it sit under pressure for a while. If the pressure drops then the radiator is leaking. If you can't find the leak then it could be inside the engine. Also a compression check in those suspect cylinders should show a problem. Bill Landsborough ---- "Love is patient and kind; love is not jealous or boastful; it is not arrogant or rude... Love bears all things, believes all things, hopes all things, endures all things." 1 Corinthians 13:4-7