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Should I replace the oil pressure sender unit

 
Old 09-30-2007, 05:58 PM
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mbb993
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Default Should I replace the oil pressure sender unit

while I'm there? I have read many posts on this subject and it is very confusing what is NORMAL function of the pressure gauge. Seems it is somewhat variable.

Not sure if this is abnormal function or not but I will describe it. Pressure guage will peg at startup then when warm come down to between 2 and 3 and will peg above 5 when engine revs above 2K. My mechanic keeps telling me it does not work because he never sees it when the car has warmed up and has suggested replacing the pressure sender unit.

I have put it off since he has had plenty of other projects to do for me as well I have planned the dreaded marathon DIY in the next few weeks (plug wires, plugs, rotors/caps) So, perhaps I should I just replace the sender also at that time or am I wasting my time/money?

Also, if I do replace it what is the OEM part VDO or FAE?

Thanks!
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Old 09-30-2007, 06:16 PM
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clinchy993
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It sounds like the same thing my o/p sensor was doing then on one of the hottest days of the summer about 4 weeks ago ,stuck in a major traffic jam it let go and faded to nothing (heart stopping moment) So my advice do it,because the drive home with the gauge going from 0 to 5 bar and back to 0 every time you change gear will do your head in
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Old 09-30-2007, 07:54 PM
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ppashley
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Search "Geolab" 's posts. He had some experience with this type of thing.
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Old 10-01-2007, 12:10 AM
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JasonAndreas
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Originally Posted by mbb993 View Post
Pressure guage will peg at startup then when warm come down to between 2 and 3 and will peg above 5 when engine revs above 2K.
That is 100% normal the way it is supposed to operate.

Originally Posted by mbb993 View Post
My mechanic keeps telling me it does not work because he never sees it when the car has warmed up and has suggested replacing the pressure sender unit.
What does your mechanic not see when the car has warmed up?
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Old 10-01-2007, 02:43 AM
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Mike J
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You can replace it but its a bit of a bear without the engine out...its way back at the rear of the engine near the breather plate.

Has your mechanic put a oil pressure gauge on the engine while it is running to accuratly see what the pressure is vs. what the gauge tells you?

When the engine is cold you will get higher pressures since the oil is at the thicker end of the range.

Cheers,

Mike
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Old 10-01-2007, 07:30 AM
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mbb993
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Appreciate all the input. From what I have read here, I figure I would need to take off the mass airflow sensor and right side intake to get to the sender.

Originally Posted by JasonAndreas View Post
That is 100% normal the way it is supposed to operate.


What does your mechanic not see when the car has warmed up?
He just sees the gauge peg high when initially started up but this typically lasts only a few minutes until the engine is slightly warm then it drops down to 2.5 or so at idle.

[QUOTE=Mike J;4627244]You can replace it but its a bit of a bear without the engine out...its way back at the rear of the engine near the breather plate.

Has your mechanic put a oil pressure gauge on the engine while it is running to accuratly see what the pressure is vs. what the gauge tells you?[QUOTE]

Nope.
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Old 10-01-2007, 04:07 PM
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Originally Posted by mbb993 View Post
He just sees the gauge peg high when initially started up but this typically lasts only a few minutes until the engine is slightly warm then it drops down to 2.5 or so at idle.
And then it will peg high (4-5) when the revs go above 2k?
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Old 10-01-2007, 05:33 PM
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mbb993
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Sorry for the confusing post Jason. I wrote it in a rush and was not as clear as I should have been but thank you for your responses. I just took the car out for a spin to get all the details down.

To clarify the problem. When the car is cold and first started up and idling the pressure gauge will peg all the way up above 5 and stay there. After a five minute warm up it will come back down to around 2.5-3 at idle but pegs above 5 at rpms above ~1200 then comes back down to 2.5-3 at idle again. My mechanic never sees the gauge when the car is warm so he sees it pegged above 5 "all the time" which lead him to the conclusion the sender needs to be replaced.

Anyway, it is the original part AFAIK so he may be correct. It does seem a bit more sensitive than you would expect. It seems to jump up quickly and not gradual as the rpm goes up. I will probably just replace it with the other work I have planned.
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Old 10-01-2007, 06:33 PM
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Mark

This sounds absolutely normal for a 993, mine does exactly the same. Jason and Mike are right to question your concern. I can only assume your mechanic does not see many Porsches go through his shop - I'm not a mechanic but I think he's mistaken........and you're worrying unnecessarily.

Trevor
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Old 10-01-2007, 07:31 PM
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Originally Posted by Trevor-uk View Post
Mark

This sounds absolutely normal for a 993, mine does exactly the same. Jason and Mike are right to question your concern. I can only assume your mechanic does not see many Porsches go through his shop - I'm not a mechanic but I think he's mistaken........and you're worrying unnecessarily.

Trevor
+1 - exactly the same as mine. Stop worrying, start driving!
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Old 10-01-2007, 09:57 PM
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mbb993
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OK, guys!
I was not concerned about it and didn't think it was malfunctioning but after being told by my wrench a few times that it was broken I began to question my eval. I'll continue to ignore him!

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Old 10-14-2007, 12:48 PM
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Default update!

Here's the latest on my current project. After visual inspection of the sender it showed a lot of corrosion on the connection points. Decided since I was in the vicinity to change it out so to reduce the need for return journey to the center of the earth anytime soon!

I pulled it out with the attached housing and changed the sender and housing gasket. This also required removal of the AC bracket which in a my95 at least is attached to the same mounting bolts. That made routing the spark plu wires that much easier.

Observations:

Old sender operated as described above. One additional thing I noticed was that with the ignition switch ON and the engine OFF the pressure gauge was pegged at max >5. I read somewhere this may be abnormal (IIRC a post by Jason?)

New sender: Ignition switch ON engine OFF = 0 reading.
Cold start @ 750rpm = 4
After warm up @ 750rpm = 1.5-2.0
runs up smoothly now with engine revs
@1000rpm = 2.5
@ 1500rpm = 3
@2000rpm = 3.5
@3000rpm = 4.5
>4000rpm = 5

So, perhaps my wrench was not completely wrong. I think the old sender was still usable but not functioning entirely normal. After all the searches reading posts, I also believe that no two senders operate exactly the same!

I am happy with mine at least for now and glad I changed it.
Thanks again!

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