Lower end knock that goes away after a oil change

EYEWONTCRY

MEMBER
1999 CHEVROLET ASTRO
6 CYL
AWD
AUTOMATIC
124,000 MILES

I have been having a lower end knock that goes away after a oil change, I am noticing a lot of sludge, but it started knocking after a water leak, I changed the water pump. And the water goes low after a 40 to 80 mile trip, only loosing about a quart of water, there is no visible water leaks though, as for the off and on knock I think the oil pick up is sludged up! Is there any way to clean the sludge with out dropping the oil pan? Also my awd light is off and on, although there don't appear to be a problem, why would the light come on, could it be ow on gear lube, is there a way to check, my haynes manual does not cover awd?

Saturday, May 24th, 2008 AT 9:05 PM

1 Reply

SQM

MECHANIC
6,383 POSTS

Hello,

Engine oil slug can be cause by moisture in the oil, also if the oil gets overheated for extended period of time. Keep in mind that a bad crankcase ventilation system can allow moisture into the engine.

If the sludge is bad enough it surely can impact the oil pressure and the oil pump will not be able to pick up sufficient amount of oil and that will lead to little to no oil at the top part of the engine. This will create noticeable noise.

https://www.2carpros.com/articles/high-or-low-engine-oil-pressure

As for cleaning out the sludge, the best option wild be to remove the oil pan and clean. Typically, the chemical oil flush will not get out all the sludge (if it is severe enough to clog oil pump or the screen).

Also, it is important to keep in mind that, unless you fix the issue of why you are getting sludge into the oil, even after cleanout the sludge will return.

I have attached the oil pan and pump removal procedures below.

Please let me know if you have any questions.
Thank you.

Images (Click to make bigger)