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Discussion Starter #1 (Edited)
My '97 Eldo's oil pressure light started to flicker when the engine was hot and I was stopped at a light. The dealer determined that I needed a new oil pump which he changed. The problem still persists. Now the dealer says it must be due to worn bearings in the engine. The engine runs fine and has never produced a knock or any other noise. I have only used synthetic oil for the past 5 years. Does this seem logical? Also, I have changed the oil religiously every 3000 miles since the car was new. The mechanic who replaced the oil pump also commented how spotless the inside of the engine is. How can bearings be worn to the point of reducing oil pressure. The engine has 95,000 miles on it.
 

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White Diamond 2001 STS
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Oh man -- this is such a common problem. The fix is a $30 oil pressure switch from the dealer. I can't believe they changed your oil pump. That must have been a costly repair. They could have/should have verified oil pressure at the switch by installing a mechanical gauge first. That would have indicated that your oil pressure is fine (as it likely is), it's just the switch that needs to be replaced.

The synthetic oil isn't helping -- it's already thinner than most conventional oil. You may see that light go out by using a quality conventional oil formulated on the thicker side (like a high mileage 10W-30 or Shell Rotella T 10W-30). Else, just replace the switch and drive on. Your bearings are fine. The bottom end on a Northstar is incredibly robust.

Welcome to the forum! Wish you had reached us first before the dealer changed out your oil pump! I'd actually try to get some of your money back on that oil pump -- especially if they did no diagnostic work up front, and just ASSUMED that was the problem.
 

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Discussion Starter #3
Actually, the switch was replaced first. The dealer put a pressure gauge on it and it read 9lbs. They did refund my money for the pump (after a bit of arguing back and forth). They also tried 20-50w oil. They also tried adding Lucas Oil Treatment. Nothing seemed to work. I did try raising the idle a little (just enough that the check engine light wouldn't come on). That seems to keep the pressure light from flickering on.
 

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I thought the oil pressure switch was set for 3 psi. Does anyone know what idle pressure actually should be and what is a normal reading at 2100 rpm.
 

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Actually, the switch was replaced first. The dealer put a pressure gauge on it and it read 9lbs. They did refund my money for the pump (after a bit of arguing back and forth). They also tried 20-50w oil. They also tried adding Lucas Oil Treatment. Nothing seemed to work. I did try raising the idle a little (just enough that the check engine light wouldn't come on). That seems to keep the pressure light from flickering on.
9 psi is just fine. Spec is 4 or 5 psi, if read at idle. It's supposed to be 4-5 psi at idle, and either 20 pr 30 psi at 2000 RPM I believe. I will check when I get home, if someone doesn't post the correct spec sooner.

Something is amiss in that pressure switch circuit, and I believe a new switch would fix it, even if they say they've already replaced it. If they told you that 9 psi was too low and causing the switch to read low, try another dealer. It's plain as day in the service manual what the correct pressure is.
 

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What are they going to suggest next? Engine replacement? I am surprised that they changed a pump at 9 psi. Then again, maybe I am not.
 

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Sedan de Ville, CTS
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After your arguements (discussions) with them, and the apparent incompetence, I would quietly go to another dealer. Sometimes I fear that a mechanic will sabotage my car at the next opportunity. And I am not even paranoid. By the way, I normally work very well with dealers and mechanics. ????
 

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........this same problem is one or two threads up or down from this one........same solutions, too.
 

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Discussion Starter #11
When my problem first appeared, I took the car to my local Mobil station and told them to change the switch. They changed it and the problem persisted. I then took the car to the dealer and had them check it out. They confirmed that someone had already changed the switch, so I know that it was changed. Then they seemed to give me some incorrect information. Thay said that they put a pressure gauge on it and that it read 9 lbs. and that anything under 11 lbs would trip the light, so they changed the oil pump and charged me over $900.00 (which they did refund me later). This didn't help the problem at all. The guys on this forum have confirmed for me that GM says that at idle the minimum oil pressure should be 5 lbs. So if the dealer was right and found there to be 9 lbs. at idle, then my oil pressure is fine. So now I have a new switch and a new oil pump and the problem persists. Thicker oil and oil additives haven't helped either. I am sure that the oil pressure is fine in the car but I don't know what is tripping the light. If the pressure was truly low, the engine would be making lots of ticking noises, if not knocking, especially at start-up. It runs and sounds perfect. If anyone figures this out, please let me know. Thanks. Rich
 

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Rich, I replied also in the other thread. You didn't say up front that the Mobil station changed the switch the first time. That aftermarket switch is likely the problem. It's either bad out of the box, or not calibrated correctly. I would install a genuine ACDelco pressure switch and see if the problem persists. It likely won't.
 

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Discussion Starter #13
Hi Jadcock,

I thought of that too but what are the odds that my original switch and the new aftermarket switch both behave in the exact same way. I am thinking that something else must be tripping the switch, but I just don't know what.
 

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It's either the switch or the wiring. There's really nothing else in that circuit. They have proved that the oil pressure is okay (9 psi at idle). The only things that would to make the light illuminate include:

* low oil pressure
* bad switch
* bad wiring
 

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2000 STS RHD 194,150 miles. what's a speed limiter???
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i had a similar problem 5 years ago with a '97 eldo.
at hot idle the light would flicker on and off and sometimes the stop engine message would appear.
i changed the switch and the problem was still there.
i fitted a shop pressure gauge and found that i had a good 7psi at hot idle and way over 40psi at 2000rpm.
i fitted a second new switch and still had the problem.
i couldn't understand how the shop gauge showed good presssure and the switches were showing bad.
i decided to fit an aftermarket oil gauge, to do so meant adding some plumbing fittings to the filter housing that routed the pressure switch feed round the motor mount.
with the oil switch and new gauge sender routed around and down the side of the motor mount i never had the low pressure light come on again and the dash gauge showed the same readings as the shop gauge.
the only thing i could think of that caused the problem was that maybe there was a pressure drop at the switch due to the thermostatic oil cooler which has its feed right next to the oil switch.
moving the switch away from the oil cooler feed maybe stabilised the pressure at the switch.
 
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