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Thread: oil pressure

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    Default oil pressure

    Ok so, I have a 97 TJ with the 2.5L. When I first start it up (yes it starts slow but that is a separate issue), everything seems to be working properly. All gauges are reading normal but, after about 15-20 mins of the engine running my oil pressure seems to drop of while at idle. Once I give the engine a little gas the pressure starts to go back up. I've tried different weight oil and the same problem occurs. Any suggestions?

    Woodie

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    Senior Member Sr. Beaver's Avatar
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    Is it an electric gauge, if so try to install a mechanical one from any parts store and see if it does the same, could be a faulty gauge. I've ran into that over the years and now keep a mechanical gauge in my tool box just for that reason.
    Last edited by Sr. Beaver; 02-17-2010 at 09:59. Reason: can't spell
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    MODERATOR warrior's Avatar
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    (1) replace your oil sending unit.
    (2) try 20W 40 or 50 oil.
    How many miles your engine have?
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    I'm running about 109,000 on the engine so far...I'm actually thinking about doing a engine swap with a Chevy 305. I just don't have time before I move to Colorado.

    Beav, thanks for the heads up on this...the dealer told me "it's normal, don't worry about it"

    Woodie

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    Land Squid Jeffb_79's Avatar
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    I'd start with replacing the sending unit.
    They seem to be pretty notorious for going bad.

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    Senior Member HillBillE's Avatar
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    I too prefer mechanical guages, much more accurate.

    How far does it drop off? It is normal for the pressure to drop a bit on an engine with higher milage, once the oil warms up and the engine hits operating temp.

    If it's 45lbs at start up, and drops to 20 when warm, your still OK.

    I've had rigs idle at 8-10 lbs, and go up to 40+ when revved.

    On a newer motor, or a full rebuild, the pressure should be higher, and not have such a large drop once warm.

    My CJ's 258, with under 5K miles since it's rebuild, holds 60-70 lbs at start up, and drops to 45-50 once warm (at idle)


    I'd advise you to stay away from a 'high volume' pump. It won't do much for the pressure, but it will pump the top end full, possibly starving the lower end.

    If the mechanical guage shows low pressure, and it's not smoking bad, using oil, or having blow-by, I'd try a new/rebuilt oil pump.


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    Wheelin requires wrenchin Doppler's Avatar
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    Quote Originally Posted by usmcboomer View Post
    ...the dealer told me "it's normal, don't worry about it"

    Woodie
    Yeah it's normal when parts begin to wear out; they make more money with an engine replacement than replacing an old sending unit!

    I agree with Warrior change the old sending unit, make sure you inspect the oil port when you remove it to see if it's just plugged up with gunk. If so you may be able to clean it and reuse but I would recommend just changing it.

    Also concur with Sr. Beaver that the mechanical gauge is the best way to go for pressure reading.

    Do you hear any knocking or tapping from the engine when the pressure drops on the gauge? If so, you could in fact be losing pressure at the pump either because of faulty pump or clogged screen, cleanliness of sending unit port will give you indication of what the oil pan may look like. Good luck and keep us posted.

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    Thanks for all the help guys..to answer HillBillE, oil pressure falls completely out. I'll check out the sending unit once it actually gets a little warmer out here in PA...still fighting with about 30 inches of snow on the ground here. I also need to check out all of my wiring, I have a nice electrical gremiln also...I love the jeep but she and I are fighting pretty good.

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    Also, keep in mind that the stock oil pressure gauge, is more of a dummy light than anything. It's not really giving you an accurate measurement of your oil pressure.

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    General rule of thumb is you want at least 10psi per 1000rpms. As your engine gets tired, the pressure will start to drop off. It's caused by parts wearing out and tolerances opening up. Do as others stated and test with a mechanical gauge. If oil pressure drops off too much, you will start to get a rattle or knock. Be careful on how thick an oil you put in it too. Too thick equals pump can't push it through the galleys and you will starve it for oil when it's cold. Stay within what the manufacturer recommends for oil weights.
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