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The Guru's oil consumption writeup up close


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The decrease in oil consumption to reasonable levels after an engine flush is a ringer for gook in the rings.  The three ways that lots of oil can get to the combustion chambers are the PCV line, the rings, and the valve guides.  Valve guide problems are rare in Northstars.  Stuck rings are not uncommon.

One thing that can cause stuck rings is the use of cheap oil at oil changes.  This can happen without the owner's knowledge.  Another possibility is the oil "change" really just being a topping-off, a problem often occurring with overfilling and oil foam going through the PCV valve.  If stuck rings go on too long, it's hard to get out all the shellac.

The FSM for most GM engines since... forever gives a quart every 2000 miles as the maximum tolerable under warranty.  About half that is probably a good number for a well-maintained engine.

Northstars don't have any reason to burn more oil, to any extent, as they get older.  They use steel sleeves, like a lot of newer aluminum engines, and the cross-hatching in the bores is carefully designed to keep the rings free while controlling the amount of oil that is used by being burnt in the upper part of the cylinder.  The cross-hatching doesn't change noticeably over the life of the engine, which can be several hundred thousand miles.

Your oil consumption figures seem to add up to about 16 oz total every 2000 miles, which is tolerable in a new engine.  If you are catching 10 oz of it in a catch can, you are doing OK with the rings.

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  • 3 weeks later...

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I really don't want to start an oil thread again here. I just want to comment about synthetics and dino oils and the use of additives.

Over here in Europe a synthetic oil costs twice as a dino oil and just about the only kind of oil available to the ordinary Joe is synthetics or semi synthetics. Synthetics works fine when you have turbos or superchargers and need that little extra temperature safety but it is completely unnecessary in a Northstar engine. The older Northstars (and any older engine with flat tappets, gear type oil pump and distributor gears) need higher levels of additives designed to handle the high contact pressures in those areas and since the newer oils with for instance API service grade SJ has a lot less of those additives (remember ZDDP?) they are not suitable for an older Northstar engine that was built when the latest API service grade was, for instance, SG. I had a discussion about that with the Guru and he claimed that an early generation Northstar could use up to viscosity 15W-40 oils without harming anything. If it was hard to find an oil according to the older API grades then I could for instance use an oil suitable for gasoline AND diesel engines because diesel engines requires more wear protection additives.

The reason I write this again (I started a thread in the Swedish sub-forum a couple of years ago) is that I have read a lot of posts lately where people claim you can use the latest oils without problems and some people even insists that all talk of the ZDDP additives is non-sense. There will always be people that compare what they have to do with their car with what the neighbor had to do with his 75hp Opel or whatever and believe that the solution that includes the minimum amount of work and thought also apply to their own car. Remember that the earlier Northstar engines were designed 25 years ago and that they were the strongest FWD vehicles on earth. Naturally technology has developed since but that doesn't mean that you can use todays oils in yesterday’s engines because the oil development has moved to a point were car manufacturers no longer uses flat tappets, gear type oil pumps and distributor gears which in turn renders previous high amounts of ZDDP obsolete.


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I agree 100% Jan, thanks for adding your experience from the guru.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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