Engine knock and oil rating

[LinkMJB]

Hi, I just changed my friends oil today on his 1995 Nissan 240sx. The guys at Autozone told me to use 20w50 for a car with it's amount of miles (250,000) so I went with Valvoline 20w50 (the special blend for high mileage vehicles) and replaced his oil. They said to replace it with 4 quarts because it's a 4-cyl. So, I remove his oil and it's thick as sludge and only amounts to 1 quart. I remove his old oil filter, replace it with a new one and fill up his crankcase with the new oil. His car runs better than before we go pick up some pizza, then come back and park. We then go back out a couple hours later and now it's making rattling sounds (directly under the oil cap, I assume it's a rod from reading other posts due to low oil pressure). Now, how can I fix this problem before it turns into something really bad? I won't let him drive it because I don't want the rod to get screwed up. Is the weight of the oil improper? Did I not use enough quarts of oil? Also, why did it take a couple hours to tell that it has problems... why not right after the oil change? If anyone could help, I would really appreciate it. What weight oil should I use, and how many quarts? Thanks a lot, and hope to hear from you all soon.

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[benemorius]

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[NISTECH]

First of all you need to wallop you buddy for not changing his oil at proper intervals!! That in itself is likely what the problem is.

Secong dont base the # of cyl in car to how much oil it holds, you put 4 qts of oil in a 4cyl 2000 and up sentra 1.8l, the pistons are going to be floating, the car holds a meare 2.9 qts with a filter change.

I would say start light on the oil and see if you have any leak issues and move up from there. I think 10w-30 would be a good starting point but by no means do I think the weight of the oil put in it caused this problem . As he stated in your duplicate thread its probably cause the sludge was dampening an already existing problem from lack of oil changes. It may bee the tensioner is done or the passages to it are plugging up with the fresh oil moving sludge around in the engine.