Chrysler Repair: repair, insulator surfaces, plymouth lazer

Question
this is a plymouth lazer question, but there is nobody registered to ask it too, so i hope you can help.
it's a 91 lazer with a 1.8 ltr sohc engine with 160000 miles on it. recently its been burning more oil than usual and the oil pressure drops sharply at idle when the cars warmed up. the cylinder head has been replaced, i don't think its a valve because i pulled the spark plugs and there wasn't any kind of oil deposited on them. there was more of a white deposit caked on them. there is some engine noise sounds like a valve but i don't know. any help you can give will be great.

Answer
Hi Bob,
I don't have any experience with that engine so I just can go with my general knowledge. The oil pressure drop when hot can result from: worn parts in the oil pump, too thin (inappropriate grade) or diluted oil (from coolant or fuel leaking into it), excessive bearing clearance (due to genralized wear), oil pump relief valve stuck (remove and clean). The whitish deposits on the plugs may indicate the spark timing is too advanced or that the cooling system is running too hot, but if the plugs insulator surfaces aren't blistered it may not be too excessive a temp to worry about. But it would be good to check the spark timing with a timing light to make sure that it is at specified setting which should be shown on the underhood sticker. You could be hearing pre-ignition detonation (ping) due to an overly advanced spark timing.  
I would smell the oil for the presence of gasoline and also look to see if it appears milky which would indicate water leakage. If that is not present, then I would try changing the oil to the next higher number weight grade to increase the oil pressure in the system when it is warm, which may be low due to internal engine wear. Low oil pressure will also produce various valve noises due to inadequately pumped valve lifters.
I am assuming that you have changed the oil filter so that it is not plugged up. While the oil gauge is working it might be off-calibration and giving you a too pessimistic reading, but with the mileage you have on it, I think it is time to increase the weight grade of the oil to make up for wear of the bearings and cylinder rings. That may quiet things down and reduce the oil consumtion. I also have read about using more expensive oil designed for high mileage engines but I have not tried it or read any evaluations of its effectiveness. But increasing the weight grade may be the least expensive thing to do first.
Let me know what results you get or other things you try that help.
Roland