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Tool Talk Discussion Forum

How to tell if a oil sending unit is bad on a car?

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Bob G

01-17-2004 16:16:37




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I have a 95 Olds Auroa with the 4.0 V8. The manual says the oil light will flicker at idle when the engine is hot. The other day I drove to town the engine was a operating temp and run into work to drop something off. When I came out the digital alarm was on saying 0 oil pressure. The engine didn't sound light it had 0 oil pressure, no lifter noise at all. I changed oil since it was due. My wife said it did it again the other day at a stop sign. My question is since it only does it when warm could it be the oil sending unit? I would thing if it was the oil pump it would probably do it when cold also.

Any ideas appreciated.

Bob G

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Bob G

01-18-2004 16:14:35




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 Re: How to tell if a oil sending unit is bad on a in reply to Bob G, 01-17-2004 16:16:37  
I'm beginning to think it is electrical. Today I drove the same distance and at an idle is was at 25 pounds, which is what the local dealer said it should be. At 60 mph it stays right at 60 to 65. From doing a parts search at Rockauto.com there is also a relay between the gauge and sending unit. I am going to call my mechanic and talk to him tomorrow and see what he thinks.

Thanks for all the input.

BobG

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tech4

01-18-2004 09:39:48




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 Re: How to tell if a oil sending unit is bad on a in reply to Bob G, 01-17-2004 16:16:37  
I would put a mechanical gauge in the sender port and see what the real pressure is. I have seen a clogged oil screen cause the pressure to be just a few psi and the engine would run fine until it completely clogs.



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MarkB

01-18-2004 04:00:37




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 Re: How to tell if a oil sending unit is bad on a in reply to Bob G, 01-17-2004 16:16:37  
In my experience, bad oil pressure senders almost always leak. That's because the diaphragm inside is ruptured. Typically they will read OK when cold, because the oil has leaked out of the unit. As they warm up, the oil pressure will drop or fluctuate as oil leaks past the diaphragm.



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Pappy

01-18-2004 01:10:25




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 Re: How to tell if a oil sending unit is bad on a in reply to Bob G, 01-17-2004 16:16:37  
On my Fords, I have just unplugged the single wire on top of the sender and grounded it. The gauge will show maximum pressure. I then replace the sending unit for 3 or 4 dollsrs.



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Mac

01-17-2004 18:28:27




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 Re: How to tell if a oil sending unit is bad on a in reply to Bob G, 01-17-2004 16:16:37  
BoB: Do you know if that model has the low/no oil sensor in the pan??? Some of the newer ones I know, have them. Fact is it has to be reset everytime you change the oil. If it has this type swx, maybe it has gone bad. Otherwise as suggested, get a manual guage and see what the true reading is.



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Brian G. NY

01-17-2004 16:27:53




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 Re: How to tell if a oil sending unit is bad on a in reply to Bob G, 01-17-2004 16:16:37  
Oil (even the best) thins when it gets hot. So....oil pressure is sure to be much lower at an idle when then engine is hot. The gradual drop in oil pressure as the mileage increases is pretty much a natural occurence although it can be speeded up immensely by such things as running the engine hot, running it low on oil (even once) or allowing the oil to become extremely dirty between changes. The easy way to check you oil pressure is to buy and install a "mechanical" gauge in place of the sending unit. This can be done with a limited number of fittings and tubing right under the hood or, do an underdash installation so you can continually monitor the real pressure.

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Robert

01-17-2004 16:23:32




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 Re: How to tell if a oil sending unit is bad on a in reply to Bob G, 01-17-2004 16:16:37  
If it was your oil pump, I think that you would have blown a motor by now, I would point you in the direction of a certified and reputable machanic. I suspect that your electrical system is not working properly, or something like that. If you do anything at all see a good mechanic and have him look at the car, they usually have the right tools and can diagnose the problem within 60 minutes or so. but if you try to fixit yourself be very careful, newer cars arent as easy as the 1970s models are to fix.

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James in North Carolina

01-17-2004 21:06:59




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 Re: Re: How to tell if a oil sending unit is bad o in reply to Robert, 01-17-2004 16:23:32  
My truck was reading almost 0 oil pressure last year. The problem was a loose oil pressure switch. I tightened it up and all was well.



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