97 STS oil pressure light

[AndyCaddyinfo]

I am selling my 97 STS to a local youngster. It has been a great car for me over the past 11 years.

I just bought a used 2010 DTS.

The STS has 88K miles on it, with the famous (and unrepaired) half case seal leak/seepage (1 qt every 800-1200 miles). No big deal. The car still drives well, overall.

I recently had oil changed by dealer (since I was there, anyway), and I later noted on receipt that they put in 5-30 oil. I have always run 10-30 in the 97.

Anyway, I now get the occasional flickering oil pressure light, only when stopped at light and in gear.

Engine temp stays normal, with no "check engine oil level" warnings. Oil level looks good (Add mark). No unusual engine noise.

I would like to figure this out before I sell the car.

Questions:

Could this be due to the 5-30? Maybe just a switch? Bad oil pump? Worse?

What should I ask my local Caddy mechanic as far as diagnosing the problem?

Any ideas would be appreciated. Thanks...

[Cadillac Jim]

I would look at the oil sending unit, which is on the oil filter adapter. If it is good, you might want to check the oil pressure with a gauge before you go back to 10W-30. There is so little difference between 5W-30 and 10W-30 at operating temperature that you really need to look at the cause before you just go back to 10W-30. There is some possibility that the case half leak includes an internal leak that lowers your oil pressure at idle, but, if so, it isn't serious, but I would want to put a gauge on it and see for sure if it was my car.

I've run 5W-30 Mobil 1 in my 1997 ETC (same motor as your 1997 STS) almost since the first oil change when I bought it new. I started running 5W-30 in it when my dealer told me that it was OK right after I bought it new (in Southern California) and have used 5W-30 ever since.

[AndyCaddyinfo]

Thank You, Jim.

And appreciate all of your (and everybody else's) contributions to this site over the years.

[BodybyFisher]

I would get rid of the 5W30 ASAP, its too thin for a 97 and no doubt the reason you are getting the oil pressure light. The older engines can have an oil pressure problem, mine had it and I needed to run 15W40 to stop it from coming on. Your pressure could have been borderline with 10W30, putting in 5W30 probably put it over the edge and the light came on

[AndyCaddyinfo]

Thanks. I will defifitely check oil sending unit, likely change back to 10-30 just to see.

[Cadillac Jim]

The key to the oil sending unit is, is it leaking around the seal? If so, it's been hit by road debris or a wrench or something and isn't accurate anymore.

[rockfangd]

also check to be sure it does not have a fram filter installed. i cant tell you how many times I see people put on the fram filters and have a oil light come on at idle. when cold it is fine once it warms the light starts to flicker and become more steady. I had it happen on my eldorado.

Also that engine will consume 5w30 a bit quicker than 10w30, especially with a crankcase leak

[airmike]

I recall some service bulletin about overfilling with oil and running the engine to get something unstuck I believe. My daughter had it done to her eldorado a few years ago and it did fix hers. Someone chime in here hopefully because I don't remember what it entailed. Sorry I can't be much help, I didn't do it, and she was gone to college. I just remember getting to pay for it:huh:

[BodybyFisher]

I recall some service bulletin about overfilling with oil and running the engine to get something unstuck I believe. My daughter had it done to her eldorado a few years ago and it did fix hers. Someone chime in here hopefully because I don't remember what it entailed. Sorry I can't be much help, I didn't do it, and she was gone to college. I just remember getting to pay for it:huh:

That is the truth, but that is for NO oil pressure, not low oil pressure. Sometimes the pressure relieve valve can stick open, overfilling the system purges it

5W30 is way to thin for a 99 and older NS, it calls for 10W30, while that does not seem like a big deal, the thinner oil in this engine is a problem especially when its very hot.

I have never torn down a NS, but the oil has to get up from the pump to the top of the engine through the oil manifold and case half and any internal leaks will drop oil pressure to the point of turning the light on.

While its nice to check the oil pressure sender, it never helped my NS, only 15W40 helped it and I always used AC Delco oil filters.

[AndyCaddyinfo]

Thanks for all of the replies.

My Caddy mechanic pressure tested the oil pump, said it was pumping at less that 10, and that oil pressure switch was leaking. Thought that the 5-20 was probably the cause.

I had them replace both.

My only question...he advised that I should be running (and they actually added) 20-50 oil in this 14 year old engine engine at this point in time, apparently due to oil useage noted in my original post here. This place works primarily on older Cadillacs, and I trust him, but I am also not really concerned about some seep and blow-by.

Anybody think anything different, about maybe 10-40?

[caddypete]

I would agree 5-20 is to light of an oil, 20-50 seems a little heavy unless you live in a climate that never sees cold temps. 20-50 is what I run in a air cooled Harley in the summer.

[Cadillac Jim]

The owner's manual and factory shop manual explicitly say not to run oil with the top number higher than 30, as in 20W-40. The "30" as the top number gives the viscosity range with a warm engine. They don't say why, but too high a viscosity will lead to under-oiling, and the pistons and valves are oil-cooled, so running the engine really hard with 20W-40 or 20W-50 could lead to scoring or seizing of the pistons and valve train.

That's true of older engines, too. I put in some 20W-40 Castrol in my 1986 Escort and found that running the car really hard resulted in a tappet losing its prime. After the engine cooled down and warmed up again, it was OK. I went back to 10W-30 and never had another problem. Until I ran a green light and was broadsided; the car had only one dent - but that dent went clear through. But the engine was fine.

When in doubt, go with the manufacturer's recommendations.

[AndyCaddyinfo]

Thanks Jim and Pete....

[winterset]

Thanks for all of the replies.

My Caddy mechanic pressure tested the oil pump, said it was pumping at less that 10, and that oil pressure switch was leaking. Thought that the 5-20 was probably the cause.

I had them replace both.

My only question...he advised that I should be running (and they actually added) 20-50 oil in this 14 year old engine engine at this point in time, apparently due to oil useage noted in my original post here. This place works primarily on older Cadillacs, and I trust him, but I am also not really concerned about some seep and blow-by.

Anybody think anything different, about maybe 10-40?

If you don't mind, what did the mechanic charge to check, and replace the oil sensor. I have had the flicker for some time, in addition to I believe the leaky "O" rings on the filter/sensor unit. I purchased a OEM sensor, but still need the "O" rings. I am thinking I am OK to do this job, but if I can get the mechanic cost, I will decide what route to take. Also please keep us informed if it really fixed the problem

[JimD]

Since you are selling the car, this will not help you much but it might help some future reader.

....My Caddy mechanic pressure tested the oil pump, said it was pumping at less that 10,....

Less than 10 psi @ idle is not a problem. Here are the Northstar oil pressure numbers:

Oil pressure specifications from 1998 Seville Service Manual page 6-14 and 2004 Deville Service Manual page 6-15;

Minimum pressure at normal operating temperature at idle RPM = 5 PSI

Minimum pressure at normal operating temperature at 2,000 RPM = 35 PSI

....and that oil pressure switch was leaking.

Different issue. Oil pressure senders fail and the only reliable replacement part is OEM. Aftermarket oil pressure senders are NOT calibrated for Northstar idle oil pressure.

...he advised that I should be running (and they actually added) 20-50 oil in this 14 year old engine engine....

Bad advice as far as this driver of a 13 year old Northstar is concerned.

I do my own oil changes and blend my own mineral oil visocity using 4 quarts of ROTELLA 15W-40 plus 3 quarts of Starburst 10W-30. Final (theoretical) viscosity is close to 12.8W-35.7. This blend not only reduces the oil seepage but also provides a healthy dose of the additives that have been removed from Starburst oils in the past 10 years.

[AndyCaddyinfo]

Thanks-

100 (1 hr) bucks initially for checking pressure and subsequent switch replacement....pump replacement and camshaft seal set 250 more (2.5 hrs).

I have driven the car long and hard three times since repair, no oil pressure light...although seems slightly lower MPG.

I will obviously let you know if any changes after I switch back to the 10-30, as I will take the advise on the oil viscosity and change it.

[BodybyFisher]

Given that the oil pump I see at rockauto is $117, $250 including parts to install it, is amazing. The crank pulley must come off, along with the monstrous CAM cover, you are saying labor for replacing the oil pump was $133? Not sure how that was done but that is an amazing price, who did this a friend?

So you are saying that the 5W20 is still in there?

I find it hard to believe that an oil pump caused this problem, did he disassemble it and look for scoring and tolerances?, see if you can get it from your mechanic I would pay for you to ship it to me

I think this could have been a loose crank bolt also

[AndyCaddyinfo]

Probably was not clear, but overall total was $450, less tax....camshaft seal added more, I think.

Oil pump was used...really didn't matter to me, as car is getting sold tomorrow to the son of a friend. I have loved this car for 11 years, but I want it out of my driveway, as I have the 2010 DTS I just bought.

This place does a lot of work on older Cadillacs, including rebuilds, head gaskets, halfcase seal leaks, etc.

I am no expert, or I wouuld have done it myself

The 20-50 will be coming out. I am getting this car to it's buyer tomorrow....$2800.

[BodybyFisher]

My guess is that the oil pump did nothing and that the 20W50 is what stopped the light, I had NO idea 20W50 was used, I thought it was just suggested, not actually used, I thought you had 5W20 in there

[AndyCaddyinfo]

10-30 will tell, then. I will let you know.

[AndyCaddyinfo]

To clarify, 5-20 was in there unbeknownst to me after dealer oil change (When buying my 2010). I have always used 10-30.

Shortly after that, the oil pressure light started flickering at idle.

I switched to 10-30 to see if there was any change. Oil light still flickering at idle after 15-20 minutes of driving.

Recent repair, 20-50 recommended and added. No flicker.

I will have new owner switch back to 10-30 immediately, and will advise.

Thank You for all of the advice.

[BodybyFisher]

Benny, can you see if the mechanic still has the pump and if he does, I would LOVE to have it. This low oil pressure problem has been irking me for a long time, my 96 had the problem.

I would LOVE to take that pump apart and check its clearances....I would LOVE to examine it closely and report my findings to the board. I would pay for shipping, it would be a big addition to this board if we could identify a bad pump, we have been told that these pumps DO NOT go bad, so your pump will be very telling, Thanks, Mike

[AndyCaddyinfo]

I'll see, let you know.

Thanks for all.