Poor/zero oil pressure @ idle - suggestions?

[boyo]

Last week I bought a '72 911T in decent shape, which the previous owner said he was "going to drive until the engine died" and replace with a 3.2 or something. At the time it had good compression and oil pressure (at least I think it did) so I figured I could squeeze another year or two out of it with some bandaids, then upgrade. He said it always ran a bit hot, though.

Yesterday I pulled up to a stop light and watched (in horror!) as the oil pressure dropped down to ZERO. Rev the engine, pressure goes up. Idle, no pressure. While driving I could see pressure from 20lbs to 60lbs depending on the RPMs. Luckily very close to home, where it's now parked.

The oil tank level was fluctuating, but read only 1 quart low at idle. I added a quart but the pressure still remained poor. I did observe the tank level rise, so I'm reasonably sure it works.

My thoughts at this point are:

1. Pressure sensor broke

Doubtful, since it does register different pressures for different RPMs

2. Clogged oil system / oil pump

Oil filter full of gunk, or bad oil pump?

I high centered getting into our garage a few days back. Could be I pinched off the oil line under the passenger side - but saw no visible signs of damage.


3. Bearings? What bearings?

The engine runs pretty well, with no unusual noises. I doubt the bearings are worn enough to zero out the oil pressure, at least I think I'd know there was a problem.


Any ideas where else to look? Thanks!

-Boyo (aka Dennis)

[Kurt B]

Hope it's not a problem. Mine's at zero at idle too and has been since I got it in 1998. In fact, I think it's supposed to be! When you rev it goes up to 3 or so at the most and when you let off it drops to around zero.



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Kurt B
1984 Carrera Cabriolet
911 Page
carrera_cabriolet@yahoo.com

[john walker's workshop]

if you can get 60lb out of it, hot, then the low reading at idle is kind of a minor problem. the engine's probably not as tight as when new. the guage isn't real discerning in the 0-10lb range. the oil light comes on below 6lb. so does it?

[lendaddy]

My '77 930 does the same thing. Not to woryy I dont believe. I read once that Porsche even had in the owners manual on some of the cars that "it would be normal for the oil preesure light to come on occasionally at an idle" I may be wrong but I think I read that in excellence a year or so ago. My light has never come on and I see 60 plus at high rpm warm. But it does rot barely above zero when hot at idle. Kinda scary but you get used to it.

[boyo]

The oil light did NOT come on, so I guess that's good news! Yeah, it's hovering just above zero, and it was extremely hot yesterday. It wasn't as hot outside on the test drive day, 80F versus 105F yesterday so that could have a lot to do with it.

Huh, I thought I read in the manual that anything below 70psi was cause for shutting off the car immediate. Or was that *above* 70psi? I'll go check it again... I was trying to read it while driving, so I could be mistaken. Thanks all,

-Boyo

[Early_S_Man]

Boyo,

Bruce Anderson has commented on this oil pressure at idle 'problem' many times. If your oil pressure meets the latest spec book criteria ... at 194 degrees F, 56 psi at 5000 rpm ... don't worry about it at idle!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[rstoll]

I would suggest an oil and filter change. Castrol 20/50 or equivilent.

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Robert Stoll
83 SC
83 944

[lsolon]

My 72 does the same. freaked me out when i rebuilt it 7 yrs ago until my mechanic basically said what s_man said. Still going strong after 45,000 hard miles

[orbmedia]

I drove a '73 targa for years with this so-called "zero" oil pressure. Not only that the oil would get very hot, like in the 250-270 range. Never posed a problem and the motor was always strong. Don't worry about the pressure at idle, just be concerned about the pressure at spec RPM.

[Joeaksa]

Dennis,

The "standard" of the German mechanics when I drove a 911 in Germany is as follows: One bar (14.7 psi more or less) per 1000 RPM's with the oil at normal temp.

They always told me to check it at 4000, where you should see 4 bar, or 60 psi. Anything else did not matter in their eyes, as long as the oil pressure light did not come on and stay on. This is from the factory guys in Zuffenhausen...

I would do an oil/filter change and see how it looks and to make sure that the motor has the correct amount and weigh installed. I have used syn oil for years and if you are running A/C on the car you might look into this. Otherwise use a good brand of oil (have heard that Castrol has been implicated in premature wear, so would look elsewhere) in the motor and keep driving it!

Keep the oil temps below 230 with dino oil or 250 with syn oil and you will be fine.

Joe

[rstoll]

You have "heard" about Castrol and premature wear? Well, I have actually "used" Castrol in my Volvos for 15 yrs. Sold two of them with over 200,000 miles on them and they didnt use a drop of oil. I sold one at 230,000 and the guy traded it in a year and a half later at over 300,000 miles. I kinda like Castrol.

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Robert Stoll
83 SC
83 944

[stevelb]

Listen to Warren. Don't worry about it. Not too long after I purchased my SC, I was driving down 95 on my way home from the Inner Harbor, 98 degrees, A/C going full blast, rush hour stop-n-go traffic. When I exited the freeway and came to a complete stop I noticed my oil pressure at zero and the little green light illuminated. Called my mechanic and he said don't worry about it...read your owners manual. My SC manual states at 5000 rpm, the pressure should be about 4.0 bar (about 60 psi). The manual further states, "At idle speed with the engine oil hot, it is permissible for the green control light to light up-".

I switched to synthetic oil shortly thereafter and while my pressure will still hover between 0 - 1 bar on very hot days, in traffic with the a/c blasting, the little green light has not come on since. Thousands of miles later and all is well.

Up-Fixin volume V has an interesting article on oil pressure ant the 917 center fed oiling system. With this type of oiling system, the 917 only needed 34 psi at 10,300 rpms since the oil did not have to overcome the centrifugal force to feed the bearings!

[john70t]

Had that question with my new 2.2 1970t a month ago.

Oil light would come on below 500rpm, but gauge wouldn't register: except high rpm cold.

Some fusebox problems, but a Porsche parts dealer said oil-gauge calibration problem for a early 911 was normal.

Probably best for the soul to take out the oil-pressure switch, put in an accurate gauge, and find out from the source itself.

[Joeaksa]

Robert,

Your Volvo is not air cooled the last time I looked. The three Volvo's I have owned always needed antifreeze in the winter, something that my 911 never asks for! Different motor and different requirements.

I like and have used Castrol in various water cooled cars for years and like their products. Started to use it years ago in my first 911 and had some problems, and emailed a very knowledgeable person in the Porsche world and his first question was, what kind of oil are you using? Seems that various people have had cam/valve wear with Castrol oil in the 911 motor. No need to name him but everyone knows he is one of the 911 "guru's"...

Glad you are happy with it, I use Mobil One and have had not one problem in over 15 years of syn oil. My 911 motor is too expensive to experiment anymore!

Joe

[rstoll]

Yeah, but Mobil 1 might get a little expensive in a '72 unless he has a good way of recycling it off of the garage floor.

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Robert Stoll
83 SC
83 944

[Joeaksa]

Robert,

No more expensive in my 85 3.2 than it was on my 72 with a 2.2 or 2.4 installed! Fix the oil leaks and Mobil One is not expensive. Its a lot cheaper for me to replace my oil every 5000 miles and spend another $30 than to overhaul it earlier in its life after the oil let me down.

I have A/C on my car and sitting in a traffic jam has my oil temps 230 degrees and above at times. With syn oil I will let it get to 250 before shutting the A/C down, but with ANY dino oil my personal max is 230 degrees.

It all comes down to personal tastes and I prefer to spend a bit more money on syn oil and hope that it extends my motor life. Hope I am right!

Take care,

Joe