Engine Knocking sound after warm up

  • 4.3L
  • V6
  • 4WD
  • 194,000 MILES
My blazer starts good. After start-up, the engine sounds quiet but as it starts warming up, a knocking/ticking sound starts to appear. When cold, the oil pressure reads about 60 - 70 and after warm up/ driving, the pressure reads from 20 - 38 at idle. Of course the pressure will go up when I rev the engine or taking off. I opened the driver side valve cover and it seemed to be clean with no sludge but I still took out the rods and sprayed through them with the chem tool carburator cleaner. One of the lifters somehow popped up a little after I sprayed it with the cleaner, that I had to turn the engine so I can re-seat the rod. It was the first lifter towards the front of the vehicle. Since this side wasn't that dirty, I chose not to mess with the passenger side valves as there's too many hoses and AC stuff in the way.
The thing is from what I've researched online, it seems that, if the lifters or rods were bad, the noise should exist no matter the engine temperature, or exist when cold and go away when warm. When I listen around the engine, with a dowel or a long piece of metal, no noise from the valve covers or the top of the engine. I can't really use the dowel or the wire to listen to the front part of the engine due to all the belts, so I just lean in and listen and it almost sounds like it's coming from the area where the two bigger pulleys are at. Biggest pulley being the center one and also the other one to the right of it. (Sorry for my description as I don't really know which is which other than to guess that the biggest pulley would be the one attached to the motor itself).
I recently bought this vehicle with 194000 miles on it. Changed the oil and filter right the same day and saw it was fairly dark oil with a little sludge but no metal shavings. I put in Mobil 1 high mileage 5w-30 and an engine repair additive. One week later about 77 miles into it, I changed the oil and filter again. I used fram filter both times. Still not seeing/ hearing a difference. The engine is not losing power or dying on me but I'm concerned this may lead to bigger problems if I don't nip it.
Once again folks, I ask for your help in getting this figured out. Symptom is {engine is quiet when cold, starts knocking sound after warm, regardless of rpm, idle or run. And knocking speed follows the rpm as well}. My vehicle is a 1996 Chevy S10 Blazer; V6; 4.3 liter; Vortec; 4X4

Thank you
Do you
have the same problem?
Saturday, September 13th, 2014 AT 1:27 PM

1 Reply


These engines are roller cam and lifters so it normal for them to make a little noise at idle. Also, it could be a wrist pin that is seized up.

Since there is no sludge in the engine I don't think the oil pump pick up is clogged but you never know.

Lastly the oil pump pressure relieve valve could be stuck which means the engine needs a new oil pump. You will need to remove the oil pan and pump to see whats going on.

Here are diagrams to help (below)

Please let us know what happens, we are interested to see what it is.

Cheers, Ken
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Thursday, June 29th, 2017 AT 2:12 PM

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