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What is acceptable hot engine oil pressure at idle for a 1999 northstar engine?


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I have a 1999 Deville that I bought with bad head gaskets. Ended up finding out block was cracked. Found a 1997 engine that I went through, put Norm serts in and new gaskets, new head bolts, and new rod bolts. The crank measured good, barely any wear and all bearings plastigauged around 0.0015 clearance, well within the acceptable wear limits. Anyhow, engine runs good, sounds good but when I let it run for about half an hour and the oil gets warm at idle the oil light starts to flicker. I put my other sending unit in there and it does same thing. I put a gauge on there with a tee for oil sending unit and at just under 10 lbs the oil light flickers. Raise the rpm just ever so slightly and it jumps right up to 15 to 20 lbs or more. I have searched the internet and found a few sources that state 5lbs is acceptable oil pressure at idle. I can buy that but why would the light trigger just under 10 lbs if 5 lbs is acceptable. I think it should have at least 10 lbs at idle as most my other cars have that. I have also read that as a rule of thumb on any engine you should have 10 lbs for every 1000 rpm. I'm using quaker state 10w30 oil as I've read you should use a good oil and at least 10w30 weight oil. I'm new to the northstar engine and just want a long lasting repair as I hope to be able to drive this car for several years. I hope someone who is familiar with rebuilding these engines can give some info here.

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What oil filter are you using. I use strictly Delco filters due to the chance of slight restriction with other filters. Just my personal preference.

Have seen it more than once with your exact issue

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Could be a oil pressure switch problem. Pull the connector and check for oil in the switch. If you have oil in the switch replace the switch and see if that keeps the light out.

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

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Brakeclean the oil pressure switch connector out.

I Believe it turns the light on below 5psi. This weekend do an oil change and install rotella 15w-40 diesel oil in. That should take car of the light.

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I have read all of your concerns about the oil pressure at idle and 10 psi per 1000 rpm and concur, I have the same concerns, especially in an aging engine. If I recall, we had a NS engineer here and he said that the switch threshhold was 8 psi. I hope KHE sees this an adds his recollection of the gurus statements on this.

Could be the oil pressure switch or wiring resistance as OCT noted.

Since you measured the main bearing clearance you broke the block apart. Upon reassembly did you replace oil manifold gasket?

Did you replace the oil pump or inspect it?

One idea however. The bolt that holds the harmonic balancer in place also secures the oil pump affectively locking it to the crank shaft, if that bolt is not torqed to spec, the oil pump can slip. At higher RPMs the light would go out. How did you torque that bolt? If I recall it gets touqued to a specific torque figure, then a torque angle of 120 degrees is applied (one leg span of the harmonic balancer)

How did the lifters look when removed from the engine?

Are you using synthetic 10w30?

It would be very interesting to see your actual oil pressure. The next engine I have with this flicker I plan to check the actual oil pressure

I have my friend using a 50/50 mix of Rotella 10W30 and Rotella 15W40, but in the winter use 10W30 if you are in a cold part of the country. His 98 flickers when the engine is hot around 220 at stop lights and the thicker oil raises the oil pressure slightly turning the light out.

Your flicker problem is very interesting to me given that you tore it down and checked bearing clearances.

By the way, as you know the 99 has lifters that are direct contacted by the cam lobes. There is significant oil sheer in the 93 to 99 rubbing element lifter engines. It is this rubbing metal to metal that consumes zddp or zinc, the anti-wear compound in the oil to mitigate engine wear. When the NS was designed the anti-wear compound zinc or zddp was 1200 to 1500 ppm which has since been dropped to 800 ppm in the current API starburst "SN" which is probably what the Quaker State is that you used. The Rotella oils have at least 1200ppm zddp or zinc, I recently spoke to Shell's technical group and confirmed that. Shell also told me that all the muscle car guys are using it to protect their lifters, if they are the rubbing element type. This is not as critical with the 2000 and newer NSs that have roller lifters. The increased zddp zinc is another benefit of using Rotella.

Pre-1995 - DTC codes OBD1  >>

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

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

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I thank everyone for their responses so far, I'm using a Purolator filter at the moment.

As far as the sending unit switch goes, I started with the one that was on my replacement engine and swapped it with the one that was on the original engine that had the cracked block, same results. I was curious at what psi the switch would trigger the oil light so I bench tested both switches with an air regulator, a pressure gauge and ohm meter. I would say it is 7-8 psi as one of you stated. No oil in the top of the switch or the connector. I also currently have the switch connected with a tee and an oil pressure gauge. When engine is first started cold I have 60 psi or more depending on the engine rpms. As the engine temp warms it slowly drops and when engine is good and warm 208-220 degrees pressure slowly falls below 10 psi at idle and light begins flickering. I'm not using a synthetic, just plain conventional 10w30 Quaker state.

I had this engine all apart, the top end looked great, I suspected someone may have reworked the heads before. The valves and seats looked great all the lifters were in great shape and no flat spots in any of them compared to the engine I took out with the cracked block. Great info about the anti-wear compounds zinc and zddp.

I did not replace the oil manifold gasket or channel plate I believe its called? I cleaned it well and put very thin beads of silicone over the old ones when I assembled it. I have since wondered if that is a possible problem. I'm not sure if any of those passages are under oil pressure, looks like one is oil drain back and one is oil pump suction, not sure what other passage is.

I inspected the oil pump and relief valve and they looked great as well. I read the posts about the damper pulley bolt not being tight enough and causing oil pressure problems so I made sure it was tightened and torqued correctly when I re-assembled the engine. That whole design there leaves something to be desired.

So at this point I'm not sure if I should pull the engine back out and look it over or put the heavier Rotella oil in it?

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I believe your problem is with the oil manifold given that you didnt replace it, given that you checked bearing clearances, swapped in 2 switches and inspected the pump and relief valve and torqued the damper bolt.

If the seals on the oil manifold leak internally you can drop oil pressure. In this video Tim states that the pump can suck air if the seals are bad, I also believe that a slight oil leak on the pressure side will droo the oil pressure enough to turn the light on.

See this video. Filter out the negativity directed at the dealer, and just look at the oil manifold info. I believe the oil manifold forms oil delivery gallies and an internal leak is catastrophic.

And put an AC Delco filter in, we have heard problems with aftermarket oil filters.

By the way welcome to caddyinfo and its nice to see the good work you are doing.

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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