Low Engine Oil Pressure

Tiny
RUSSELL WINDSOR
  • MEMBER
  • 2007 CHEVROLET TAHOE
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 159,000 MILES
On March 4th, this past Saturday, I purchased a used vehicle listed above it is the LS flex fuel model from a used car dealer. It is the "police edition", so this is part of my worry with my problem.

Anyways, to the point. On startup with cold engine, I get around thirty eight pounds of pressure according to my gauge. As my engine warms, it drops down to about twenty pounds of pressure in regular driving (1000-2000 rpm). Then at idle, such as a ref light or stop sign, it sits right on twelve pounds of pressure. No noises, nothing abnormal. The oil pressure when I would give it gas would always be above the recommended(what I read online) ten pounds times 1000 rpm. If I hit 4000 rpm, my oil pressure hits about forty five to fifty. No check engine lights. I just changed the oil the day after I purchased it. Oil levels have not dropped at all since and I have put almost four hundred miles on since. No oil on the ground.

That part above is before today, when I took it to the service department of my local Chevrolet dealership. They hooked up their gauges and determined it does run a little low but my oil sending unit was bad. Had them replace that as well as the screen below it. Then, I took off to try to get to work. Noticed it would not go above about twenty four pounds of pressure, even if I punched it up to 3500 to 4000 rpm. It now idles at about eight pounds of pressure, according to my gauge.

I returned it to the dealer to reassess the problem. He hooked his computer up and it was reading about twelve pounds of pressure at idle (computer reads "bottom end" oil pressure?), When he revved up to about 3000 rpm the pressure climbed with it on his computer screen. Now they tell my "a cam may be trying to spin out" and there is nothing more they can do except put a new motor in it for me. For at least $8,500.00.

So, I called off work and returned home. I now have a check engine light code P0521, which is the code for low engine oil pressure. The engine still does not appear to be making any noises. No knocking or clanking of any sort, even idling at eight pounds.

My question(s) is, what should I do now? I am going to change the oil again this weekend, maybe use a thicker oil? Or maybe add a product for low oil pressure, such as a Lucas Oil product? Is it really possible my sensor was reading incorrectly, even though it was reading low? And my actual engine oil pressure or top end pressure was that low but the gauge was just reading it slightly higher?

I know it is hard to diagnose problems through the internet, but I certainly cannot afford to drop an engine in it right now. I have got to at least drag it out a couple of months some how. I know I can definitely get a cheaper engine not through the overpriced dealership. But jeez I am frustrated with this. Any help will be much appreciated.
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Thursday, March 9th, 2017 AT 3:29 PM

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Tiny
RUSSELL WINDSOR
  • MEMBER
I should also add that since I got it back from the dealer, I made it all the way to the interstate to get on. Gassed it a bit to get up to speed and it seemed to make this very loud whining noise. I have not had a Tahoe before this so I am not extremely familiar with what it is supposed to sound like. It was not a clanking noise by any means. But this is what made me decide to go right back to the dealer. 4000 rpm and 22 psi oil pressure.
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Thursday, March 9th, 2017 AT 3:38 PM
Tiny
CARADIODOC
  • EXPERT
I would remove the oil pressure sending unit and pop a mechanical gauge in there to see what you actually have. At first, your description matched exactly what I used to see at a very nice Chrysler dealership. They had a lot of sensor failures in the 1990's that caused low pressure readings, but the clue always was the pressure would drop at idle, then pop right back up and hold steady when engine speed was increased just a little.

On most engines, a camshaft bearing has to be really wiped out before the oil pressure will be low. A better suspect is worn crankshaft and/or connecting rod bearings. Their clearance can be checked without removing the engine. If it is excessive, you might get away with installing new bearings. If you wait until a connecting rod starts knocking, it will be too late. Once it starts that hammering, the excessive clearance will increase exponentially real fast. The journals will be torn up and they will destroy new bearings within a few seconds. You have to replace the crankshaft then, along with the bearings, but then you still have to worry about metal chips running around in there.
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Thursday, March 9th, 2017 AT 4:07 PM
Tiny
RUSSELL WINDSOR
  • MEMBER
I do not understand why the dealership would not even mention that. They told me it would nott even be worth the price to have them inspect the engine. They said I might as well go ahead and just replace the entire engine if I am going to pay the labor for that. They put gauges on both top and bottom sensors and said my oil pressure was running low but "they thought I would be alright". I will research your suggestion. My dads fairly car savvy and has driven his Silverado since brand new 1998. I will check back in this weekend with what I find. Thank you for the reply caradiodoc.
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Thursday, March 9th, 2017 AT 4:12 PM
Tiny
CARADIODOC
  • EXPERT
I replaced the crank and connecting rod bearings years ago on my 1988 Grand Caravan in a misguided attempt at solving an elusive knocking noise. It did not change anything, and that engine finally blew its first head gasket at 420,000 miles. The van was so rusty, the carpet was the only thing holding the front and rear together, otherwise I would have repaired it. (By the way, I am searching for a rust-free 1988 with 15" wheels from down south).

The only thing that might make this not feasible on your vehicle is if there is a welded-on cross member under the oil pan. If there is, you will have to raise the engine to get clearance. Normally that isn't too difficult on GM's and Chrysler's. It is a real pain on Fords.

As an alternative, you might look for a nearby community college with an Automotive program to see if they would be willing to look at it. Understand they will only do engine work when they are teaching Engine Repair, and that could be only once per year. The work has to fit what they're teaching, and it has to provide a valid learning experience. At my school, we charged ten dollars per hour for what the job was supposed to take. We got parts at real good discounts, and marked them up ten percent to form a "breakage" fund in case we damaged anything. Due to the limited number of hours the kids were in the shop, it could take a week or two to get the truck back, but you will save a lot of money.

Do not overlook the oil pump. Yours is driven by the snout of the crankshaft, and my resource even has a comment on using high-volume pumps for high-mileage GM engines that have low oil pressure. That suggests this is a common problem and the pump is a permanent solution.

As far as why the dealer wants to sell you an engine, a high-level national instructor has shared a lot of stories about "customer-unfriendly business practices", and this is one of them. They rated the top manufacturers for customer-friendly business practices as Hyundai, Toyota, and Chrysler. They put customer satisfaction ahead of quick profits. VW, Audi, BMW, and GM are at the bottom of the list. You can expect a huge bill every time you visit the dealer's service department. They might also be looking at the truck as far as rust and wear. If it is in good shape, they may feel a rebuilt engine is a good value. Be aware though, if you get a second opinion from an independent repair shop to have your engine rebuilt, I would expect it to cost half of what you were quoted.

If a new oil pump gets the pressure up, I cannot tell if it is because the old pump had excessive wear, or if it is because a high-volume pump overcomes the result of worn bearings. Logic would say if the bearings are worn, that wear is going to continue to escalate, and pumping more oil through them is only a temporary fix. To go so far as to list this comment on a parts web site suggests there is a real good chance the problem will be solved with a new pump.
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Thursday, March 9th, 2017 AT 4:43 PM

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