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Thread: 1999 STS Oil Pump Low Pressure

  1. #1
    Join Date
    Feb 2006

    1999 STS Oil Pump Low Pressure


    I'm new to the forum as I have been involved with the purchase of a 1999 Cadillac Seville STS for my lady friend's son. Two weeks later, his car is laid up with a low oil pressure warning, and a dealership telling it's going to $1,100.00 to replace the pump, and if that doesn't fix it, another $2,500.00 to pull the oil pan and clear any blockage to the pump intake tube. never worked on a STS. How difficult is it to replace the oil pump? I've found some articles on the web stating that the pump can be effected by carbon build up and that filling the engine will another 10-12 quarts and running at 3500 RPM can clear the blockage. Is this safe? Anyone BTDT and have some advice to lend? Help, my lady frind is going to kill me if she has to lay out $3,600 two weeks after buying this car for her son.

    (Preston's mothers friend...and looking to stay that way)

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  3. #2
    JimD is offline Cadillac Owners Connoisseur
    Automobile(s): '98 STS (RIP @ 206,xxx miles)
    Join Date
    Sep 2003
    Metro ATL

    Re: 1999 STS Oil Pump Low Pressure

    If you mean the idiot light (oil can symbol) on the DIC, one other possibility is a failing or failed oil pressure sending unit.

    One step would be to replace the sending unit with a new GM part (not aftermarket).

    Or, you could temporarily plumb a mechanical pressure gauge in there to measure the actual oil pressure. Should be a minimum of 5 psi at idle at normal operating temperature.

  4. #3
    Join Date
    Feb 2006

    Re: 1999 STS Oil Pump Low Pressure

    Engine was making obvious noise indicating valve lifters are being starved of oil. Dealer confirms that oil pressure is indeed low and it's a flow problem.

    After researching this forum, I'm looking to make sure the harmonic balancer is bolted tight, and if so, then overfill to force prime the pump and run for a few minutes at 3500 RPM.

  5. #4
    mcowden is offline Cadillac Owners Connoisseur
    Join Date
    Jun 2003

    Re: 1999 STS Oil Pump Low Pressure

    Preston, a dealership, as usual, is probably trying to bend you over the fender before your first date. The pressure sending unit, harmonic balancer bolt, repriming the pump, etc., you are headed in the right direction. Try Shell Rotella 15W-40 motor oil if it's only showing the pressure problem at idle, and find a reputable mechanic either way.


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