Knocking at highway speeds.

[johnnygo]

Hello I'm new here and I have a general question.
I have a 1999 G/M LS and it seems that shortly after an oil change
when accelerating on the highway I get a knocking sound. (Sounds like a rocker knock.) If I add another quart of oil the problem goes away for a week or so then creeps back. When I first pointed the sound out to the service person at the dealer he said, " It will make that sound sometimes. Thats the way the engine is." Two other dealers blew me off with that answer. I added a oil additive and the sound went away for three weeks at the last oil change. Is the dealer using the wrong weight of oil? Or too little oil for the engine?
Any help will be helpful.
JohnnyGo

[cobradude360]

do you know what weight oil they were useing?

[johnnygo]

They have been using 5w/30 with the last few oil changes. The service person said thats what the motor calls for. Will a thicker oil damage the motor? Any advise?
Thanks
Johnny Go

[cobradude360]

a thicker oil would not hurt like try useing 10w30 and you should use 5 qrts thats what i run in mine and she runs like a champ mines also a 1992 though so hope this helps

[dzus]

If this is the same place you normally go for service and it never made that sound before I would suspect the oil filter. Living in the south I would stick with 10w-30,because 5w-30 is to light for warm weather climates.

[jimmytroanoke]

Originally Posted by dzus

If this is the same place you normally go for service and it never made that sound before I would suspect the oil filter. Living in the south I would stick with 10w-30,because 5w-30 is to light for warm weather climates.

Stay with 5w. on the Mod v8. These engines have very tight clearances and passages. I have read on another site staffed by Ford technicians that thicker oil will cause serious problems on this motor due to a delay in getting oil pressure to the timing chain tensioner.