Dirty Engine Oil

[VIN]

I own a 1995 Nissan Sentra 160 (carb). Mileage 140 000km.

For the past year I have noticed that my engine oil changes colour after doing an oil and filter change. After about 500km the starts changing colour. After about 1500km, the oil is already black. Previously, after 50000km the oil still used to be good as new. Have tried using a quality engine flush, but this still does not help. Also changed oils (used Shell Helix and Castrol). However, I DO NOT need any topping of oils. Sent a sample of the oil to a lab. The report states that the oil contains sludge. Could it be the PCV valve at the rear of the engine block that needs to be changed.

What causes the engine oil to become 'sludgy' so soon? Any suggestions would be deeply appreciated.

[s13sr20chris]

you went 50000 km on one oil change? yeah, that will cause sludge. you need to do frequent oil changes(3000miles whatever that is in km) with high detergent oil. pcv valve(oem) would be a good idea as if it is not the prob it may have sludge in it anyway.

[VIN]

Oops, that should have read 5000km's. Thanks for your input.

[VIN]

Got a quote for a new PCV Valve from Nissan Agents-- R229.00 ... thats roughly $30.00. Unfortunately the local auto stores don't stock them.

[s13sr20chris]

wow, thats high. they are just a couple bucks around here.

[VIN]

Yep, In South Africa the cost of spares in unbelievably high. It would work out cheaper to import a car that purchase one over here. But the government has slapped on heavy import duties to prevent this. A brand new Nissan Almera is about R140 000 ie. abour $20 000. A good quality oil is about $20. Motor maintenance here is very costly.