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Low oil pressure in air-cooled 3.0i


Neun 11

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My 911 refurbished 30.i is in the hands of a tuner, but can't put it on the Dyno because of low oil pressure. My question, how long does it take ( normally ) for an air-cooled 76 911 to reach full temperature??? 

 

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Dont trust the old 911 sender & its wiring. Have a look at the pictures at this site:

https://www.paragon-products.com/Oil-Pressure-Gauge-p/nerp-911mopg.htm

Oil Pressure Gauge, Mechanical

Fits Porsche 911, 930 1974 thru 1989,  Ahhh, peace of mind, we love it. Now you can know exactly what oil pressure you have. Our 911 Mechanical oil pressure gauge block and liquid filled gauge will be a visual indication of the health of your engine.  0-100PSI  0-7 Bar 1 1/2" Dia. Still allows use of factory sending unit.

 

OR you can make up something yourself for not much money. BUT beware, there is a good & VERY BAD way of removing the oil pressure sender.

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From experience, I can tell you that it does take a little while (maybe 20 mins or so) and needs a good hard drive to come up to temp ...

A quicker way to warm the engine up is to place a towel over the rear air vent and rev it a little ... a few minutes is all you need with this method ... if you do this, remember to keep an eye out on the temp gauge ..

I'm very lucky with my gauges ... they work perfectly and I trust their readings .. if yours aren't functioning properly, it would be worthwhile to get them sorted ..

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Many thanks, on my recommendation, I asked him to let the car idle for longer. It was some 28 mins or so before pressure increased to a more acceptable level. He used both manual gauge, and the cars gauge, BOTH shared the same reading. As I am new to the PC scene, I am told that once warm, pressure will adjust accordingly with revs, yes?? 

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Nah, there is something wrong or a miscommunication here.

At idle and with the engine cold, the oil pressure will be around 2 Bar or so and it will slowly drop back to around 1 Bar when at normal operating temperature.  As the engine gets hotter, beyond normal temperatures, the oil pressure will continue to drop to the point where the red warning light may flash on when it gets to dangerous (to your wallet!) temperatures.

So higher engine temperatures do not increase oil pressure.

The actual pressures detailed above will vary with the oil viscosity you are using so expect some variation.

However, starting the car and driving off normally (ie a few thousand rpm) when cold should have the pressure easily showing 5 Bar.

The general rule of thumb is a minimum of 10psi per 1000rpm at normal operating temperature.  1 Bar is 14.7psi  BTW.

 

I'm wondering if your engine rebuilder has accidently dislodged a oil seal between the oil pump and the crankcase when he assembled the engine OR has left out a oil line restrictor and this is the reason for the poor pressure?

 

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Just now, Peter M said:

Nah, there is something wrong or a miscommunication here.

At idle and with the engine cold, the oil pressure will be around 2 Bar or so and it will slowly drop back to around 1 Bar when at normal operating temperature.  As the engine gets hotter, beyond normal temperatures, the oil pressure will continue to drop to the point where the red warning light may flash on when it gets to dangerous (to your wallet!) temperatures.

So higher engine temperatures do not increase oil pressure.

The actual pressures detailed above will vary with the oil viscosity you are using so expect some variation.

However, starting the car and driving off normally (ie a few thousand rpm) when cold should have the pressure easily showing 5 Bar.

The general rule of thumb is a minimum of 10psi per 1000rpm at normal operating temperature.  1 Bar is 14.7psi  BTW.

 

I'm wondering if your engine rebuilder has accidently dislodged a oil seal between the oil pump and the crankcase when he assembled the engine OR has left out a oil line restrictor and this is the reason for the poor pressure?

 

I'm wondering if they are trying to read the oil level gauge .... it will show low oil level at start up till it gets hot, then go towards the top when at temperature at idle ... it will also fluctuate downwards while driving as the oil circulates ....

Easy enough mistake to make ....

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Ronny, I was thinking the same thing but Neun said the test gauge and the car gauge correlated so dismissed that idea as you would expect them to move in different directions.

Neun,

Are you able to give some quantification of oil temperature and pressure as a function of time?

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4 hours ago, SC 3.2 said:

What is the bad way ?

The sender is in so tight it can take up to 140PSI to untwist it.

Pelican forum has examples of people breaking the block/crankcase trying to undo it on the motor.

Its easier & better to unbolt the whole mounting from the block & then unscrew the sender in a vice.

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6 hours ago, Peter M said:

Ronny, I was thinking the same thing but Neun said the test gauge and the car gauge correlated so dismissed that idea as you would expect them to move in different directions.

Neun,

Are you able to give some quantification of oil temperature and pressure as a function of time?

Hello, and no. Motor was rebuilt prior to purchase, with little or no kms added prior to sale. Cars oil pressure eventually rose over time, as for temperature, he didn't seemed at all concerned with temp. I had to add proper throttle bodies and other components. Car is ready to go to dyno, but tuner just making sure that everything remains accurate. Troubleshooting. Worse case scenario, I may source an auto sparkie while he has it, just make sure there is no issue with the gauges. 

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On 7/15/2018 at 11:46 AM, Buchanan Automotive said:

What is the engine oil viscosity that is in the engine at the moment  ? , meaning is it a 20w-50 or is it a 15w-50 or a 10w-40 or a 5w-40  or something else ?  this is a very important in regards to oil pressure 

 

Oil viscosity is a 20W/50 blend as recommended for early 911,s.

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  • 2 months later...

Update,  Unfortunately, Engine is undergoing a rebuild. The result of a very ordinary { i,m being too kind here  } rebuild previously. It is in good hands with an engine guy who comes recommended. ive been promised a great engine, that should outlast me. Build time is around six weeks, so, with that, and then getting engine refitted by my mechanic, fingers crossed its back with me just around Christmas. 

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  • 1 month later...

Update, complete engine rebuild. New oil cooler/s, should have it back in a couple of weeks..... Why a complete rebuild? The result of a poor attempt the first time by whoever sold the engine to Neil. Not blaming anyone but myself.... Just getting it done. 

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On 27/11/2018 at 08:54, Neun 11 said:

Update, complete engine rebuild. New oil cooler/s, should have it back in a couple of weeks..... Why a complete rebuild? The result of a poor attempt the first time by whoever sold the engine to Neil. Not blaming anyone but myself.... Just getting it done. 

Did you get any hard parts replaced?

 

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  • 2 weeks later...
On 28/11/2018 at 19:32, Mike D'Silva said:

Did you get any hard parts replaced?

 

Yes Mike, pistons, internal oil cooler and external front mounted oil cooler. Most of the build labourous fortunately. 

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