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Oil Pressure pegged at 5+ ?????

 
Old 07-09-2010, 10:08 AM
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altarchsa
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Default Oil Pressure pegged at 5+ ?????

I recently replaced the oil pressure sender with an aftermarket unit. The old one (original I presume) was registering pressure properly, but I thought it might be the source of an oil leak, so I replaced it.

On restart, the gauge pegged at 5+ and the red oil warning light and "!" light came on. I contacted the seller and they tested their other aftermarket units in stock a found an unusual range of readings from the terminals. They contacted the mfg and they agreed to send me a unit direct to assure that I received a good unit.

I installed the second sender yerterday and got the same result as before. I searched previous posts and found:
Oil pressure pegged to top
boxsey911
Any suggestions other than "buy an OE VDO unit"? They're about $145 vs. $35 for the aftermarket unit. I know the savings is meaningless if it doesn't work. But I just wanted to ask if anyone has any other suggestions as to what might be the problem before I buy a VDO. I'd like to not do the job more than three times.
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Old 07-09-2010, 10:23 AM
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elbeee964
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Used, they're going for $45 over at dcAutomotive. (928.606.203.01?)

Also, you replaced the old Big Black O-ring with a new Big Green O-ring, Si?...



ok - never mind. (I'll just go back to lurkin')
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Old 07-09-2010, 10:58 AM
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Rocket Rob
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When I purchased my C2, the oil gauge would peg. Turns out the fault was the wires on the pressure sender were reversed. I had to reverse the spade connectors on the terminals and all was right. I hope this helps.

Edit: Its easy to confirm which wire is which. With the power on, momentarily ground each of the two wires. One will cause the oil press gauge to move, the other will cause the oil light to illuminate.
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Old 07-09-2010, 02:20 PM
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Ken D
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^ what Rob said. The aftermarket pressure senders usually have the terminals reversed when compared to the OE piece.
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Old 07-09-2010, 05:05 PM
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You're right that I had this problem. I remember Rob chipping in to help and suggested checking the terminals but got no joy from reversing them (pegged it to the bottom instead!). It was only resolved by fitting the original VDO item that I purchased direct from Porsche.
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Old 07-10-2010, 01:11 AM
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Thanks guys. I think you hit on it with the switched terminals.

I checked the first replacement part against the VDO that was previously on the car, and the terminals are in fact reversed. The stamped letters on the cannister are easy to see on the replacement, and very obscure on the dirty VDO, but they are definitely reversed. I'll try switching the connectors tomorrow to reverse the wiring.

Since both of the replacements were from the same mfg, maybe that's the way they wire them. I'm just a little surprised that the mfg/distributor had not encountered this before, or that they didn't advise the retailer of this issue when they were alerted to my problem and sent the free replacement.

In the future, I think I'm going to make it standard practice when doing any work on my car to search the forums first and learn all the things to watch for.

I replaced the O-ring on the housing a few months ago during an engine rebuild, so no worries there. I've been able to access the sender by removing only the air filter housing and cannister and, thankfully, did not have to do the additional work to remove the housing.
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Old 07-11-2010, 04:06 AM
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Default Fixed

YES! That did it guys.

Reversed the spades on the aftermarket oil pressure sender (which obviously also resulted in reversing the wiring) and it fixed the problem. With all the practice of changing it twice, it only took about 20 minutes for the entire job.

Pressure now reads correctly, about 1 when warm/idle, about 4+ when warm/at speed, no oil warning light.

Only thing I don't understand is why the manufacturer does not install the spades correctly, or if they're different on other applications, why not at least include a warning/note to "check for polarity on your model before installation". Better yet, for a foolproof solution, why not leave the spades off, provide them in a baggie, and let the buyer install them to match their application? I certainly would have paid $.10 more, checked the labeling on the original VDO and wired it correctly the first time, given this scenario.

Thanks for your help Rennlisters!
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Old 07-12-2010, 08:38 AM
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I would like to get to the bottom of my oil pressure worries. Sometimes it is very good (5+), other times just OK ~4. I'm OK with the engine speed vs engine temp vs oil pressure relationship - these are max figures when hot.

When it first dropped to ~4 I popped some more oil in and it seemed to push it back to 5 for a while ...

I will get round to replacing the sender unit at some point, but would be interested to hear whether this is characteristic of unit beginning to fail.
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Old 07-12-2010, 10:36 AM
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Engine wear = more space between internal parts = lower pressure.

Also, hot weather = thinner oil = lower pressure. If you have a high miles car, or you are driving it in hot weather, I would switch to a heavier viscosity oil, maybe 10W-40, or even 20W-50 racing oil.

I'm not an engineer, but I think the more important reading is the low pressure at idle. If the pressure gets too low, not enough oil will circulate to protect the parts, both to lubricate them and to keep them cooler, in our "oil-cooled cars".
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Old 07-12-2010, 05:02 PM
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Cheers for tips.

Been out for a drive this evening and its pegged at 5+ most the time ??? Like I say, its the inconsistency which is the wierd thing. Reading on dashboard is best described as a little 'sticky', so wondered whether this was a symptom of what will end up being a faulty sender. From your post it seems they are straight forward to replace, so best off just getting a new one.
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Old 07-12-2010, 05:34 PM
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Hi C2dweller, welcome.

Its NOT normal for the oil pressure to be pegged at 5 at whole time, so don't expect it.

It's a generally a function of engine speed, and its also affected by oil temperature/viscosity.

So at tickover, expect a little more than one, around the houses, 4 is fine, and foot on the floor 5.

If you are seeing low pressure, i.e. less than 1, then you need to be v careful, and you should check it out. Likely is a bad sender, else you have a bigger problem.

Doesn't sound like you have a problem though.

Others please chime in.

Rgds

Phil
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Old 07-13-2010, 09:57 AM
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Originally Posted by c2dweller View Post
Cheers for tips.

Been out for a drive this evening and its pegged at 5+ most the time ??? Like I say, its the inconsistency which is the wierd thing. Reading on dashboard is best described as a little 'sticky', so wondered whether this was a symptom of what will end up being a faulty sender. From your post it seems they are straight forward to replace, so best off just getting a new one.
Replacement is pretty easy, with two levels as I see it.

Just replacing the sender, you can remove the air filter cover and housing from the MAF and get to it. I had to also disconnect the fuel line from the front end of the fuel rail in order to get a wrench on the base of the sender. I used a small Crescent which allowed me to open the wrench and locate it on the sender, then tighten the jaws to turn it. Space is tight so it's really tough to get a bite, rotate and reset. A proper size crow's foot wrench or open end wrench, maybe even with outside edges ground down to clear the temperature sender, would make it easier.

If you want to replace the o-ring on the oil sender cover plate, you will also need to remove the intake and A/C bracket. That process is described in the thread I referenced above.

Don't forget to reconnect the vacuum line to the cannister on the side of the air filter housing on reinstall.
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Old 07-13-2010, 10:17 AM
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And don't forget to be extra-specially careful to prevent any external engine crap/grime from falling into that open engine pressure sensor hole.
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Old 07-13-2010, 05:53 PM
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Originally Posted by elbeee964 View Post
And don't forget to be extra-specially careful to prevent any external engine crap/grime from falling into that open engine pressure sensor hole.
Or into the heads if you remove the intake.
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