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oil pressure/engine temperature problem...help please!!!!!

This is a discussion on oil pressure/engine temperature problem...help please!!!!! within the Internal Engine forums, part of the LSx Technical Help Section category; i just bought a 98 z28 with 35k miles. as i already posted, my oil pressure seems a tad low. ...

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    oil pressure/engine temperature problem...help please!!!!!

    i just bought a 98 z28 with 35k miles. as i already posted, my oil pressure seems a tad low. but tonight i noticed some other things, so im going to start another thread. first of all, it takes my car like 35-40 minutes to reach operating temperature. hell, it takes like 10 minutes for it even to get to the first line, which is 160 degrees. my other ls1 cars never took anywhere near this long to warm up. oh, and the temperature guage needle even went over 210 tonight to around 215, then climbed back down to 200...and this is while sitting at idle in a parking lot.as far as the oil pressure, at cold idle, it sits at around 40 psi. as the engine temperature comes up, the oil pressure goes down like normal. but tonight, it went down to 10-15 psi at idle. oil pressure is climbing like normal when accelerating, but at idle it got all the way down to 10-15 psi tonight once the engine reached the 210 mark. and i noticed that both needles are fluctuating, not just the temp guage needle. so basically, my engine is taking 40 minutes to reach operating temperature....and even when it does, it fluctuates up and down. and my oil pressure is very very low, and also fluctuates. it seems that when one needle fluctuates, the other one does too....almost like one is triggering another. can someone please chime in and help me figure this out. i have a 90 day 3k mile warranty that covers engine, drivetrain, and all electrical problems. i called and set an appointment to bring it in on friday morning. im still worried though. lil help fellas???

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    Senior Member Redphoenix1998's Avatar
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    RED
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    As far as your oil pressure, you might have a bad pressure sending unit. It's common for them to break, I broke 3 of them so far. It sits in back of the block behind the manifold and if your brake booster host or a wire tugged it loose you have an issue. Another thing may be your oil pump is bad, ie. the little O ring slipped off the pickup tube or you got something down there in the ban sifting around. As far as your temp goes, there is a coolant temp sending sensor on the front of the driver's side head that may have melted. I had this problem with the stock manifolds on and melted the coolant temp sensor. So check the sensor there, it may have some damage from the heat. Also, your thermostat might not be opening up all the way and may need to be changed. But have the dealer check these two sensors. I hope I helped you out some. Good luck. I have a 98 as well, and I've had oil pressure and temp problems

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    thanks a lot man. the car is completely stock, so being that noone has had the intake manifold off or anything, im not sure how the oil sending unit could be broken....unless of course the booster line may have done it. but thanks for the info buddy

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    Grand Imperial Wizard Sarge's Avatar
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    With the above said.....I would look at the filter first.....you may be experiancing a foobared ADBV.....I would change filters right now.....
    What oil is in there? What is the color of your dipstick? If you take a clean white cloth and wipe your dipstick on it....look closely...do you see any specs? What color is your oil? Change your filter...you may have a media collapse or a issue with the drain back valve or the bypass valve.....

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    i already changed oil and filters. im running castrol syntec 10w30 blend right now. its still acting the same way.

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    Grand Imperial Wizard Sarge's Avatar
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    Quote Originally Posted by Raise
    i already changed oil and filters. im running castrol syntec 10w30 blend right now. its still acting the same way.
    With that said....next suspect would be the sending unit....I agree with the above....I've seen bypass valves cause the same condition......but the chances of getting two bad ones in a row is remote at best....

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    Rhino21149
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    I would begin by checking the instruments themselves. The fact that both fluctuate at the same time makes me wonder if you have a bad ground somewhere in the instrument circuit. This could affect all your readings, not just when they fluctuate.

    Then I would replace the thermostat-cheap to do and if someone had put the wrong type in, fitting in backwards or something, well, that could explain it.

    Finally, while the oil pressure is low, it IS within factory range ::: of course, nearly anything is within "factory range" -- I once inquired of the dealer what was acceptable oil pressure at idle for an LS1 and was told "Anything above 7 lbs." (really). My point here is that it m i g h t just be a worn engine with acceptable if near-the-limit clearances in bearings. a

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    well the instrument theory makes a lot of sense. as far as the engine being worn, it only has 35k miles on it...it shouldnt be worn at all!!!

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    Rhino21149
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    Quote Originally Posted by Raise
    well the instrument theory makes a lot of sense. as far as the engine being worn, it only has 35k miles on it...it shouldnt be worn at all!!!
    That's not good, but 35K miles is very low for a '98. Is this the original engine? Do the #s match? -- maybe someone replaced it with a beater engine.

    I'm sure you have thought of this but you might have someone REALLY good - whp knows these cars in and out - look it over to see just what you have-chech oil pump, pickup, etc, and look at other stuff too find out what other problems you might be facing.

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    i doubt the owner put a different motor in. i took it to the dealer cuz i just bought it and it has a 90 day 3k mile warranty that covers engine, drivetrain, electrical, etc. so whatever the issue is will most likely be covered. im gonna be pissed if they come back and say 10 psi at idle is acceptable. it might be acceptable, but i know damn well the car had more psi than that when it rolled off the showroom floor. and how are bearing clearances just going to increase??

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    Senior Member Redphoenix1998's Avatar
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    the oil pump pickup is a bitch to check because you have to take out a lot of crap just to get to it. If the pressure sending unit in the rear even has the slightest wiggle, it will be the unit. Since there are no specs in your oil, I doubt your oil pump has been marred or anything but it could also be the O ring between the pickup tube and the oil pump itself. There's a change it could have been jarred loose and it's not fitted in properly or just over time it's deteriorated. It's always a possibility. Also check the breathing tubes on the rear of your valve covers, one may be loose. That could definately change your oil pressure. It's really easy to loosen the drivers side breather tube because it just connects into a rubber grommet and it's loosely held in.

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    i vote for the thermostat stuck open and the sending unit...had the oil pressure prob in my 89 iroc and it was the sending unit. your ls1 should be at op temp within a few minutes if your driving it...idle a little longer. My oil pressure is at around 30 psi at fully warm idle...cold is at 40+....driving its past the next line...60+?...mid 50's when warm.

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    well, the thermostat was replaced today and the problem is still here.

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    Senior Member Street Lethal's Avatar
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    Quote Originally Posted by Raise
    ...first of all, it takes my car like 35-40 minutes to reach operating temperature.
    Well, 35-40 minutes is stretching it a little. I'm sure we're talking 5-10 minutes, right? Even with the thermostat completely removed, the engine will reach normal operating temperature within a 5-10 minute period (provided the cooling fans aren't constantly blowing, of course).....

    Quote Originally Posted by Raise
    ...hell, it takes like 10 minutes for it even to get to the first line, which is 160 degrees.
    It's a sensor, it has to be. Being that they all work in conjunction with the computer, the temp sensor is probably giving a false reading. I did something similar (on purpose though), when I needed my old Iroc to run constantly in open-loop. In you're case though, just replace the sensor, and see what happens. I would consider a diagnostic check while you're at it, even if the SES light isn't prevalent.

    As for the oil pressure, I wouldn't trust the factory gauges as far as I could throw'em. With 35k miles, I seriously doubt it's you're oil pump. You've replaced the oil, you've replaced the filter.... now try replacing the sending unit (or have GM do it, being that it's still under warranty).

    Contrary to popular belief, you don't want to run such a fresh engine at such a low psi (oil pressure wise), as the last thing you need is a 'spun' cam bearing (even though I doubt that 'that' is the actual oil pressure's reading, I wouldn't take a chance with it though, just to be on the safe side)....
    Last edited by Street Lethal; 09-20-2005 at 04:31 PM.

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    actually im not exaggerating at all about the 35-40 mintues. sometimes it doesnt even reach operating temperature. it will just sit at 175-180. so i guess maybe youre right, its probably the temp sensor. i tried turning on the heat tonight. it got hot. doesnt the air have to wait for the engine to reach operating temp before it gets hot???
    as far as the oil pressure, gm wont replace any parts because they consider 15-20 psi acceptable. u sau u doubt that my oil pump is bad, but i hear that 98s are notorious for the oil pumps going out. as far as the oil sending unit, is that responsible for sending oil or sending the oil pressure reading to the computer??

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    Senior Member Redphoenix1998's Avatar
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    98 oil pumps are notorious for going out. I remember it being posted somewhere and the pump going out on me. It's a design flaw with those pumps, they don't flow correctly

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    Quote Originally Posted by Redphoenix1998
    98 oil pumps are notorious for going out. I remember it being posted somewhere and the pump going out on me. It's a design flaw with those pumps, they don't flow correctly
    well, the bitch is...my car is under warranty...but they say 20 psi is ok for oil pressure, so they wont install a new oil pump. anyway, considering the other night my oil pressure dropped to 10-15 psi at idle(according to the guage), shouldnt i have heard some pretty nasty valvetrain or bottom end noises from lack of oil pressure?? what does the oil pressure have to drop to before u start hearing metal to metal clatter in the engine??

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    Senior Member Street Lethal's Avatar
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    Quote Originally Posted by Raise
    actually im not exaggerating at all about the 35-40 mintues. sometimes it doesnt even reach operating temperature. it will just sit at 175-180.
    Most guys I know deliberately set the fan settings to kick in at around that temp, then re-program the ECU to lower RPM. You're experiencing something similar, but by accident, due to a faulty sensor; low temp (theoretical, the computer "thinks" it is low), high idle (realistically, the computer's "response" to it)... cause and effect.

    Quote Originally Posted by Raise
    so i guess maybe youre right, its probably the temp sensor. i tried turning on the heat tonight. it got hot. doesnt the air have to wait for the engine to reach operating temp before it gets hot???
    Absolutely. The engine is going to get hot either way, but the RPM will stay as is.... being that the ECU controls the TPS & IAC (with needed input coming from a faulty temp sensor). The engine could reach 300 degrees, but the computer will still think it's only at 170-180.

    Quote Originally Posted by Raise
    as far as the oil pressure, gm wont replace any parts because they consider 15-20 psi acceptable. u sau u doubt that my oil pump is bad, but i hear that 98s are notorious for the oil pumps going out.
    GM considers alot of different scenario's "acceptable", but this doesn't mean it's the best thing for you're engine. Let's not forget, GM is now a global entity (they're not what they once were), and although they make awesome engines, let's face it, their warranty is lame.

    After building many stroker engines myself, I can tell you with complete certainty, 15-20psi is not enough for an everyday driver. It's just a matter of time.

    As for 98 pump's being flawed from the factory, mine has over 60,000 miles on it... and has yet to be changed (pressure is steady at 45psi, with a load).

    Quote Originally Posted by Raise
    as far as the oil sending unit, is that responsible for sending oil or sending the oil pressure reading to the computer??
    The Oil Pressure Sensor does just that, senses pressure, and displays this pressure via a gauge. The Oil Sending Unit assists in priming the system with fuel (during cold start up), by informing the ECU that there is no pressure prevalent. Basically, it allows the fuel pump to work for about 3 seconds, then due to no oil pressure being 'sensed', the ECU stops the fuel pump.... until started, with pressure then being sensed for a constant feed.

    Edit: Just wanted to add, some will argue that the purpose of the sending unit is simply a fail-safe (or back-up) for the fuel pump relay. This might be possible, but then again, I never bothered to remove the fuel pump relay just to see if the engine would still run....
    Last edited by Street Lethal; 09-20-2005 at 08:13 PM.

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    thanks for your input streetlethal. well, i certainly hope my "actual" oil pressure is not 15-20 psi!!!!! im hoping its a sensor/guage problem. did u read the part about both needles fluctuating together the other night?? i was in the drive thru at taco bell, and when the engine temp would go up, the oil pressure would go down, and when the eng temp went down, the oil pressure would go up. what do u make of this?? guage cluster problem or what??

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    raise.......any updates?

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