Very strange can some one help. When I first start my blazer after sitting over night it is fine after it gets hot you stop the engine and restart it it is fine but if you let it sit for 15 min then start it it sounds like a rod knock. The oil pressure is 50 when cold then drops to very low around 15 at idle 650 rpm some times it has 35 lbs @ 2000 and some times it has 20 lbs @ 2000 rpm. It also has a noise that sounds valve chatter around 2500 rpm. It quits when it changes it to 2nd. I have a slight oil sepage in the engine oil cooler lines but not bad enough to drip oil. Could the oil cooler line couse a loss in the oil pump prime. 2000 blazer 4.3 100k on it. Even with new oil and filter.

Jerry

 

https://blazerforum.com/forum/showth...ght=oil+filter maybe this will help...