Sludge usually developes due to lack of maintenance. The question is how much sludge? There are oil backflush machines that might help, but if the sludge is heavy, you could end up doing more damage if the sludge loosens and eventually clogs the pickup screen. Best thing to do is frequent oil changes.
Thanks for your prompt reply. I have no idea how much sludge is actually in the engine. I have tried to maintain the proper maintenance, but I doubt if I did all that was required. The problem started when I did my last oil change. I was advised that since I had over 130,000 miles, I should switch to a HIGH mileage oil and since I'm not racing, I didn't need synthetic oil anyway. That's when the noisey lifters started. After about a week, I changed the oil back to synthetic. Is it possible that the high mileage oil dislodged some sludge and caused a blockage of flow to some lifters? If so, is it feasable to remove the valve covers, remove the rocker arm assemblies, remove the lifters one by one, disassemble and clean each lifter, fill with oil, and put the whole thing back together? Or just live with it.
IIRC, the lifiters are solid, not hydraulic. The use a disc on top of the lifter to adjust the clearance; multiple sizes are available through Nissan to adjust the clearance, if necessary, but I've never seen or heard of a VQ engine that required valve adjustment. Also, it will require the correct tools and it's around 18 hours of labor, book time. I doubt that the high-mileage oil did anything, but if you've been using synthetic regularly to maintain your vehicle, I, personally, would stick with it. Whether you race or not is really not a sole determining factor of using synthetic. Synthetic is primarily beneficial to engines that see extended maintenance intervals or those that see severe conditions, like heavy towing or extremes of temperature. Most synthetics are good for 10,000 miles or more (I use synthetic in my 06 Pathy, but still stick with the 7500 mi. intervals per Nissan). I also prefer to stick with a genuine Nissan oil filter. One thing you may want to do is test the oil pressure with a mechanical test gauge to make sure it's within specs. If that's good and your sure the noise isn't due to power valve screws that have fallen out, you might try some Marvel's Mystery Oil added to your oil. It's not something I usually recommend, but seem people swear by it and it won't hurt.
I would be inclined to think the hi-mileage Oil is thicker and didn't lube the valve train as well, Is it better now you switched back to syn ?
If not thenif we assume your assumption that something got dislodged, then I suggest a Flush you add to Oil, run for 20 min no load, then change Oil. I forget the brands, but available in Auto parts stores.
2003 Pathfinder from 2004 SE 4WD
1997 SER 5sp Manual from new Rear Ended 2009 !!
Gone to the Knacker yard...
New ride 3.0 manual RWD not a Nissan !!!
1997 Sentra GXE from new .... Sold 2008
2001 Sunny N16 RHD from new (N16 Nissan Bluebird Sylphy) Sold
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