: 6 of 8 spark plugs are oily!

12-08-08, 03:00 PM
Hi, my car is a 98 Deville with 260k miles.
I replaced Bosch spark plugs to AC Delco. The 6 of 8 spark plugs I took out have lots of oil. Only the #6 and #7 look good. Both #6 and #7's spark plug wires go to the same distributor.

The car lost a fan for a few months but I didn't know until last week. I guess it caused some problems.

The car may have a bad thermostat may too. I don't know how to test it but I put my hand on the big coolant hose and can feel warm at 150F and hot at 185F.

The car has somehow blue smoke and strange smell at start. It's been like that since I bought it 5 years ago but never faild SMOG test except the recent one. It faild with a very high HC @ 15 MPH. It also got high HC @ 25 MPH although it's in the range of HC. I've changed the fuel pressure regulator but not tested again yet.

Any ideas? Thanks a lot!


12-08-08, 03:22 PM
By oil on the plugs do you mean oil on the plug exterior/the ceramic insulator or the actual tip and electrodes.

If there's blue smoke and oil fouled plugs, it's either valve stem seals or piston rings. For a mid 90's northstar I'd bet on valve stem seals.

You might have a shop perform a spark/coil test to see if 3 of the 4 coils are in fact weak.

High HC is either oil burning, rich air/fuel mixture, or both. Strange smell ? Rotten eggs ? Catalytic convertor.

The warm hose at 150 and hot at 185 is perfect. The engine is meant to run at around 185 - 195.

Check your plug wiring against the diagrams.

12-08-08, 10:23 PM
sure you dont have bad valve cover rings?
when you pull the plug the oil stored up will drip down and soak the plug

Blown & Injected
12-10-08, 04:07 AM
The smoke on start up does sound like valve seals but your observation of the 2 good looking plugs going to the same coil seem to suggest that maybe you have three weak coils and the plugs are not firing strong.

Try swapping the coil positions for a pair of plugs that are easy to change and see if the two clean plugs move with the coil and if the previous clean plug location now has some oil on the plugs.