low oil pressure

[seba]

I have a 95 firebird 3.4 L. Recently my oil gauge started going down. When it was cold it was fine but when it got driven for a while and I came to a stop the oil gauge was almost at 0. The car runs good and there is no noises in the engine what so ever. Just to be on safe side I took it to mechanic and he said it is oil pump - price $405 with installation. I got it installed. It is two weeks later and same thing is happening. I am going to check the oil presure before I take it back. Can someone tell me if the oil presure check out OK, what else could it be? Can it be something serious or just a sensor. Thanks for all your help.

[MuscleCrazed]

It could be the oil pressure sending unit. You should've changed that before ever paying $400 for a new oil pump. But oh well, try that. If that doesn't fix it, you have problems.

[hellraiser319]

oil sending unit or bad guage. at least you wont hafta worry bout oil pump goin out for a long while.... there is a pressure switch on the engine for the oil that ties in with the fuel pump, and if there's not enough pressure then the switch should disable the fuel pump to prevent non-lubricated damage. mine does the exact same thing so i wouldnt worry bout it unless engine starts cuttin out.

hellraiser

[catback23]

hellraiser319: the pressure switch that ties with the fuel pump is the oil pressure sender that also feeds the gauge. It's tied to the fuel pump to shut off the pump incase of a severe accident or roll over so that fuel doesn't pump out and possibly spark a fire. I sender has to read basically near 0 pressure for the fuel pump to shut off. So low pressure will not trigger fuel shut off.

The right thing to do is to hook up a oil pressure gauge and get a reliable pressure reading. If the pressure is still low then either a major oil passage is blocked or the pump is falling (the latter more likely). If pressure is good then either the sensor, wiring, or gauge is at fault.

[xlwhellraiser]

Hey, if the major passages were cut off wouldnt the oil go through the valves and therefore smoke? I just thought of this since it happened to my car. Also, I assume that you have changed your oil. I used to get some low readings (nothing major, but still under 20) and I went and I changed the oil and put in a littlebit thicker oil as well. It totally did the magic. And also check your sending unit, it might be loose (also a problem I had), but when they are loose they usually show higher preasure.
Good luck to ya.

[catback23]

xlwhellraiser: if major passages were cut off you could also have no oil flow anywhere in the engine and thus no to low pressure. It's senseless to put thicker than required oil in to boost oil pressure because that just covers up the problem and problems that aren't fixed only get worse. In all seriousness a shop mechanic would check the oil pressure sensor and then hook up a oil pressure gauge and find the true pressure.

[xlwhellraiser]

Catback23: I understand what you are saying, but few of the mechaincs at Pepboys and few other shops really told me that if I got 10W-40 instead of 10W-30 my preassure would be OK. I was running 10W-30 and now I am running 10W-40 and the problem is fixed. One of the shops looked into my problem and told me that everything was ok with my engine . Now I was running a 79 403 with a wild cam, which might have been the reason.
Now I know that 95 bird might not need thicker oil, but its worth knowing what oil he uses. I can say that if he is running 5W-30 it might be too low. Now, from his problem the best I can tell him to do is check the small stuff first. Go to a mechanic and have them check it out. I am sure that its something simple.
Good luck.

[catback23]

it really depends on the engine and condition, if you build a motor and oil pressure isn't quite up to snuff thicker oil will help, especially if it's an older design engine. I'm saying though if your vehicle is driving good and one day you see low pressure that won't go back up to normal you shouldn't try just throwing thicker oil in. Your engine is older and generally older needs thicker, every time they make a new engine nowadays tolerances are getting tighter and things are getting smaller so generally you don't have the oil too thin problem.

Really it's a case buy case basis but for the original post the answer isn't thicker oil.

[xlwhellraiser]

However would you agree with me that 10W-30 would be better than 5W-30? I am really not sure.
When I run 10W-30 in my 89 bird it makes me feel safer.

[catback23]

depends on the engine 5w30 is thinner than 10w30. If the manufacturer suggests 10w30 then yea I would use it instead of 5w30. If the car has lots of miles and is buring the 5w30 then yea 10w30 would be better, assuming of course you don't do much low temp driving. It's all about the situtation like for me my car is a 93 with many miles on it but since it doesn't have an oil burning problem and since we have cold winters which I must drive in I stick with manufacturer recommended 5w30. Another thing with oil gaps getting tighter and smaller thicker oil just won't fit in there as well. I'm starting to see 5w20 in cars now, that's thin stuff so 10w30 and definitely 10w40 won't lubricate properly. Going with 5w30 would even hurt lubrication but just not as much as the 10w's. To sum it up it's case by case and if you got two piece of metal sliding on each other like say the main bearings you want the oil to fit in between the two parts so they have oil between them that they are sliding on instead of them having metal to metal contact. If the oils to thick not enough of it will get in between the two pieces and they will wear faster, oil too thin and they won't be supported by the oil and will wear faster because of metal to metal contact. So you need just the right weight for optimum performance.

[JDPascal]

Viscosity is a linear relationship. Because of that, it is very possible that the 5w30 could actually be thicker than the 10w30 at high operating temperatures. Such a situation would probably require oil temps above 250F though.

Although 5w30 and 10w30 oils can be used interchangeably in most cases, the best reason for a 5w30 oil is startup lubrication. Cold starts where the engine has not run for many hours as well as the low temperature (-30F) startup lube improves as the first number in the SAE viscosity rating gets lower.

Sometimes fuel dilution will play a part in low oil pressure, especially if the vehicle does a lot of short trips where the engine does not fully warm up.

That 5w20 oil recommendation makes me suspicious of marketing tricks to increase dealer shop traffic for oil changes and ultimatly engine repairs from increased wear. (just because I'm parinoid doesn't mean they aren't out to take more of my money)

I think that a 5w30 synthetic might give a similar effect as the 5w20 at getting the oil into the small clearances and still maintain a better lubrication film. I think I'd bet my warrenty on it if I owned a vehicle with a 5w20 recommendation.

JD

[catback23]

JDPascal: You some kind of oil engineer? I realize all you say but for the 5w20 I wouldn't bet my warranty on it, it's not worth it and I know the odds are against me. There is a reason why manufacturers recommend certain oil viscosities, if you think your smarter than the engineers that designed the engine then you can go ahead and use whatever oil you want. As for me I'm not gonna question what weight oil to use for a new or fairly new engine that they built. Now if the engine is old well it's worn and no longer the specs they made it to.

This is getting to be a long thread on oil. Basically use whatever you wanna use, throw some diesel fuel in there if you want. I'm just gonna say my engine is gonna last longer than yours if you do.