Oil Pressure Warning Light on Intermittently
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Oil Pressure Warning Light on Intermittently in Past Cadillac Vehicle Discussion; I have a weird issue with my Oil Pressure warning light. + It only comes on when the transmission is ...
  1. #1
    nebulosity's Avatar
    nebulosity is offline Cadillac Owners Fanatic
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    Question Oil Pressure Warning Light on Intermittently

    I have a weird issue with my Oil Pressure warning light.

    + It only comes on when the transmission is in drive and the car is completely stationary or barely moving
    + When the transmission is in drive and the car is moving, the light goes off right away.
    + When I put the transmission in park, the light goes off right away.
    + The light tends to flicker most of the time and only becomes a solid light after its been flickering for about 30 seconds
    + The light seems to be triggered when I'm turning the steering wheel as I finish pulling into parking spots

    What's strange to me is the fact that the transmission seems to have an effect on the engine oil pressure... or at least it's having an effect on the circuit that's triggering the warning light. I didn't think they were related...... right?

    I looked it up in my shop manual and it says the light comes on when the oil pressure varies within a standard deviation of the acceptable pressure range (I think it was 4 psi or something.. I don't have the manual in front of me.) I checked the oil just after the light had come on, and it looks relatively okay.. it's up against the top mark of the full range, but not beyond it.

    It looks like theres a trouble shooting procedure for this, but before I go through all that, I wanted to find out if anyone has had a similar problem and what their solution was.

    Thanks in advance.

    PS: I went to the DMV this morning, and the stupid person was really picky about reading vin numbers... they need two, and there were a couple numbers on the dashboard plate they couldn't read very well, so they sent me away and told me to have CHP verify the vin numbers. Here's my caddy at the DMV:

    gIMG_3795.jpg

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  3. #2
    csbuckn is offline Cadillac Owners Master
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    Change the oil. The oil isn't at the right level or is too thin. That or the sensor is messed up. I only had a quart of oil in my van when the light started flickering and I must have read the dipstick wrong, very embarrassing as a mechanic. Drain and get some decent oil, maybe 10/40. Also, try another dmv, that's what I did when I didn't like the answer from another. The person makes the difference.
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  4. #3
    outsider is offline Cadillac Owners Connoisseur
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    Re: Oil Pressure Warning Light on Intermittently

    If you're sure the oil is good and at the right level could the engine be idling too low? Maybe it's idling low and that's why it doesn't pump enough oil when under load (in drive) or turning the wheel (more load because of power steering pump resistance.)

    Just a thought.
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  5. #4
    nebulosity's Avatar
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    Re: Oil Pressure Warning Light on Intermittently

    Quote Originally Posted by csbuckn View Post
    Change the oil. The oil isn't at the right level or is too thin. That or the sensor is messed up. I only had a quart of oil in my van when the light started flickering and I must have read the dipstick wrong, very embarrassing as a mechanic. Drain and get some decent oil, maybe 10/40. Also, try another dmv, that's what I did when I didn't like the answer from another. The person makes the difference.
    I just changed the oil at the end of July... I think it was the Valvoline high mileage 10w30. Despite my engineering background, I'm embarrassed to say I don't understand a thing when it comes to the _w_ viscocity designations. How do I find out what the best weight is for San Jose weather? Hottest in the summer is like 100F, coldest in the summer is like 35F.

    I think I may just go to the Los Gatos DMV instead.

    ----------

    Quote Originally Posted by outsider View Post
    If you're sure the oil is good and at the right level could the engine be idling too low? Maybe it's idling low and that's why it doesn't pump enough oil when under load (in drive) or turning the wheel (more load because of power steering pump resistance.)

    Just a thought.
    It idles between 700-800 rpm. Should be okay, right?

    Yeah, my power steering makes a little bit of a hum when I'm pulling into a parking space. There's quite a bit of fluid in the reservoir, but I think I'll double check it and top it off when I get home.

  6. #5
    Mark 78 Coupe is offline Cadillac Owners Fanatic
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    Re: Oil Pressure Warning Light on Intermittently

    I had a 1980 Fleetwood years ago that did the same thing. I could never figure out what it was (did the oil change, checked level, etc.) I eventually sold it to a local guy who continued to drive it for at least a year longer, and it ran fine. Weird.
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    Re: Oil Pressure Warning Light on Intermittently

    Quote Originally Posted by Mark 78 Coupe View Post
    I had a 1980 Fleetwood years ago that did the same thing. I could never figure out what it was (did the oil change, checked level, etc.) I eventually sold it to a local guy who continued to drive it for at least a year longer, and it ran fine. Weird.
    \

    I'll eventually have to figure out somehow. I might need to go through the diagnostic tree for the warning light. It's funny because you'd think I'd be excited about debugging it, but I hate debugging circuits. LOL

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    Mark 78 Coupe is offline Cadillac Owners Fanatic
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    Re: Oil Pressure Warning Light on Intermittently

    It scared me at first because of course I thought the engine was going to implode. I got the car for $100 (back when it was worth at least $2500) from a tow company as an abandoned car. It came with no keys, and of course no guarantees. For the price I figured it was worth the gamble. It ran perfectly, just did the weird warning light thing like yours is doing. By the way, if it matters, I put the wrong year in. It was a 1990, not 1980. I drove it for a month or so before I sold it just to be sure I was not selling someone a time bomb.
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    Re: Oil Pressure Warning Light on Intermittently

    This common to the 307 Olds-equipped cars. On those cars, other members have reported fixing the issue by replacing the oil pump. The pump puts out less pressure as it ages. You could try going to a 5w40 for now.
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    nebulosity's Avatar
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    Re: Oil Pressure Warning Light on Intermittently

    Quote Originally Posted by jayoldschool View Post
    This common to the 307 Olds-equipped cars. On those cars, other members have reported fixing the issue by replacing the oil pump. The pump puts out less pressure as it ages. You could try going to a 5w40 for now.
    Yeah, I was thinking it was mostly likely the oil pump too. When I resolve the issue, I'll be sure to post the solution. Thanks, Jay!

  11. #10
    AElayyat's Avatar
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    I'd start by replacing the oil pressure sending unit.

    It's a quick & not pricy fix. Make sure to get a GM unit, I have had issues with aftermarket ones.

    Hopefully it's an easy fix, good luck.
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  12. #11
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: Oil Pressure Warning Light on Intermittently

    I'm leaning towards oil pump too. The HT-4100 are known for going through them since they are aluminum, I had to do mine last summer. It seems like the light is coming on when the engine is hitting it's lowest RPM's , which seems mechanical, not electrical.
    The other possibility which is equally as much of a PITA to fix is worn out bearings with too much clearance.
    I'd probably drive it until it gets worse, just keep the rpm's up.
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  13. #12
    csbuckn is offline Cadillac Owners Master
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    Re: Oil Pressure Warning Light on Intermittently

    Maybe take the pressure switch out and see if its gummed up
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  14. #13
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Oil Pressure Warning Light on Intermittently

    It sounds like the trans is just dragging the idle down too low. The ISC is supposed to take care of that. That's what the relearn process is supposed to address. I'm sure the 700-800 rpm idle speed is in park, right? I'll bet it's down to 500-600 in drive. If you do get to verify the oil pressure it will probably be acceptable anywhere above 700 rpm and only low when the idle is lower. Valvoline high mileage 10w30 should be fine for most engines. That's why I don't think it's a cheap/thin oil issue.

    All in all I would verify that the ISC is working. I have never took the time to watch one operate but I assume you should be able to see it bump up the idle a little when a helper puts it in drive with brake on or when turning on the AC. There is a bazillion ISC threads in the FWD Deville section If you really want to understand it thoroughly.

    I was very surprised to hear that your car passed smog but CONGRATULATIONS! It must run pretty clean, so that is a very good sign that the engine is fairly healthy. Good luck and enjoy that Coupe.
    nebulosity likes this.

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