Low Oil Pressure
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Low Oil Pressure
I just had a new motor put in my 1995 3.4L v6. (when I say new, I mean one from a junkyard) I drove it for about a week and I noticed that when the car was warm, and I was stopped at a traffic light, there was no oil pressure. I found that the oil sending unit was leaking and I replaced it. Now the oil pressure never reaches zero, but when the car is warm and idling, the oil pressure is just above zero almost in the red zone.
When driving down the interstate at 80mph, the oil pressure is only about 35-40 psi. Before the old sending unit went bad, the oil pressure was always higher, usually around 50 psi, never lower than 40. And it would always be at least 20 psi when idling. My mechanic confirmed that this amount of pressure was lower than normal, but it wouldn't cause any problems and it was ok for me to continue to drive. He said it was most likely the oil pump going bad.
Now I haven't noticed any leaks, the car isn't low on oil, and there are no knocking sounds coming from the engine. The car runs fine and the only thing I have noticed is the low oil pressure. Should I be worried? Could this cause any damage to my car? What could be the cause of this low oil pressure?
Oh and I forgot to mention the car has 10w-30 high mileage oil in it.
When driving down the interstate at 80mph, the oil pressure is only about 35-40 psi. Before the old sending unit went bad, the oil pressure was always higher, usually around 50 psi, never lower than 40. And it would always be at least 20 psi when idling. My mechanic confirmed that this amount of pressure was lower than normal, but it wouldn't cause any problems and it was ok for me to continue to drive. He said it was most likely the oil pump going bad.
Now I haven't noticed any leaks, the car isn't low on oil, and there are no knocking sounds coming from the engine. The car runs fine and the only thing I have noticed is the low oil pressure. Should I be worried? Could this cause any damage to my car? What could be the cause of this low oil pressure?
Oh and I forgot to mention the car has 10w-30 high mileage oil in it.
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I think you may have found out why the engine was in the junkyard. Did it come with any kind of warranty? If your gauge was reading alright with the old engine, and the fact that the new sending unit only made a minor change, things then kinda point to the engine. Low oil pressure is due to having excessive bearing clearances, read: a worn engine. Oil pressure has nothing to do with the oil level being a little low, or having an oil leak.
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How many miles where on the junk yard motor? Did your mechanic confirm the low oil pressure with a manual gage or did he just say, ya thats low? You could still have wiring/gage issue. You need 10PSI of oil pressure per 1000 RPMs so as long as it goes up quicly the motor could be fine for a long time.
As pressure drops near zero you will get valve noise. An engine with NO oil pressure will get very loud very quicly.
No reason not to try 10w40 or even 20w50 oil once it get a little warmer. I have seen motors jump up 10 PSI just switching to 20w50.
As pressure drops near zero you will get valve noise. An engine with NO oil pressure will get very loud very quicly.
No reason not to try 10w40 or even 20w50 oil once it get a little warmer. I have seen motors jump up 10 PSI just switching to 20w50.
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In the Staging Lanes
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I think you may have found out why the engine was in the junkyard. Did it come with any kind of warranty? If your gauge was reading alright with the old engine, and the fact that the new sending unit only made a minor change, things then kinda point to the engine. Low oil pressure is due to having excessive bearing clearances, read: a worn engine. Oil pressure has nothing to do with the oil level being a little low, or having an oil leak.
Thread Starter
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In the Staging Lanes
Joined: Jun 2011
Posts: 54
How many miles where on the junk yard motor? Did your mechanic confirm the low oil pressure with a manual gage or did he just say, ya thats low? You could still have wiring/gage issue. You need 10PSI of oil pressure per 1000 RPMs so as long as it goes up quicly the motor could be fine for a long time.
As pressure drops near zero you will get valve noise. An engine with NO oil pressure will get very loud very quicly.
No reason not to try 10w40 or even 20w50 oil once it get a little warmer. I have seen motors jump up 10 PSI just switching to 20w50.
As pressure drops near zero you will get valve noise. An engine with NO oil pressure will get very loud very quicly.
No reason not to try 10w40 or even 20w50 oil once it get a little warmer. I have seen motors jump up 10 PSI just switching to 20w50.
Here is a pic of the oil pressure gauge at idle:
http://bit.ly/zJPt9Q
Sorry. That link above doesn't work. Use this one instead:
http://bit.ly/wQSnz9
Last edited by bbjk08; Feb 19, 2012 at 02:09 PM. Reason: link doesn't work
You might have a problem and you might not. The only way to know for sure what is going on is to temporarily install a mechanical oil pressure gauge. The factory gauges are not terribly accurate. On a lot of cars built starting in the early 90s they're almost useless.
That's because the manufacturers got tired of dealing with bonehead customers who came into dealerships in a panic saying "my oil pressure is high when I first start the car but it drops way down as the engine warms up!" No s&%#, Einstein... That's totally normal becasue the oil thins out as it warms up. Hence the lower pressure.
So some manuafcturers (I know that Ford did, for sure) simply install an oil pressure switch instead of an oil pressure sender and they crimped a resistor onto the back of the cluster.
Start the engine, get oil pressure, gauge needle goes to the middle. Engine warms up, oil pressure is lower but the switch is still closed, gauge needles stays at midscale. Problem solved! No joke.
Now that's not the case with your Camaro but there are a lot of variables. Where did you get the new oil pressure sender, at Autozone or another chain selling the cheapest parts available? What are the resistance specs of the sender? You could at least measure the resistances of the old and new senders off the car to see if they're about the same.
I'll have to check the gauge in my 94 with a recently rebuilt 3.4 becasue IIRC it doesn't read all that high at idle when it's hot.
Of course the junkyard engine could be really worn, especially if it was poorly maintained. I've gotten some spectacular junkyard engines and I've been totally screwed (like on the used 3.4 I bought for my 94 *before* I rebuilt the original one). This is where the mechanical oil pressure gauge will tell you exactly what's going on.
That's because the manufacturers got tired of dealing with bonehead customers who came into dealerships in a panic saying "my oil pressure is high when I first start the car but it drops way down as the engine warms up!" No s&%#, Einstein... That's totally normal becasue the oil thins out as it warms up. Hence the lower pressure.
So some manuafcturers (I know that Ford did, for sure) simply install an oil pressure switch instead of an oil pressure sender and they crimped a resistor onto the back of the cluster.
Start the engine, get oil pressure, gauge needle goes to the middle. Engine warms up, oil pressure is lower but the switch is still closed, gauge needles stays at midscale. Problem solved! No joke.
Now that's not the case with your Camaro but there are a lot of variables. Where did you get the new oil pressure sender, at Autozone or another chain selling the cheapest parts available? What are the resistance specs of the sender? You could at least measure the resistances of the old and new senders off the car to see if they're about the same.
I'll have to check the gauge in my 94 with a recently rebuilt 3.4 becasue IIRC it doesn't read all that high at idle when it's hot.
Of course the junkyard engine could be really worn, especially if it was poorly maintained. I've gotten some spectacular junkyard engines and I've been totally screwed (like on the used 3.4 I bought for my 94 *before* I rebuilt the original one). This is where the mechanical oil pressure gauge will tell you exactly what's going on.
Last edited by 1augapfel; Feb 19, 2012 at 03:43 PM.
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The thing that I just don't understand is that the oil pressure was fine for a few weeks after i got the new motor until the sending unit started leaking. While it was leaking there was no oil pressure at idle. After I got a new sending unit, the oil pressure went up to about 10 psi at idle. Before the old sending unit went bad, there was at least 20 psi at idle if not more.