sadman

hi guys,

my car is a 1994 993 c2,no air con with 178,ooo miles on her, i do all the maintenance myself from clutch changes to brakes and suspension as I like to know my car well.

I recently changed my oil and filters,
I had Porsche filters on but changed to the mahle make this time,

since changing the oil and filter I now have a worryingly low oil pressure on tick over,

before the oil and filter change pressure would be at 1/1.5 bar on tick over, it is now about .5 /.75 bar,

at revs the pressure increases to ,
2500 rpm/2/3 bar
anything much above this it goes up to 4/5 bar so this seems to be ok, it just the low engine revs/pressure that is worrying me,

can anyone shed some light onto this ?

another factor is that it is abnormally hot here in the uk at the moment but again I have been stuck in traffic and the temp gauge gone to about ten o'clock and the pressure remained at 1/1.5 bar.


this is with the engine temp at about 8 o clock on the gauge,
I have double checked my oil level and am slightly over half on the dip stick,
I am running a part synthetic 10/40 oil,

having checked it out as far as I can, I find that the thermostat oil filter if a Porsche part has some sort of non return valve incorporated into it where as the mahle does not, could this be the issue ?


any views help is much appreciated

Quadcammer

I would run a thicker oil (and synthetic at that), but if you have consistently used this oil, that can't really be the issue.

Perhaps you have a bad filter or the bearings are on their way out.

Any strange noises?

have you verified oil pressure with a mechanical gauge?

sadman

hi Quadcammer

hopefully not bearings as they were fine prior to the oil change and to my knowledge they don't go that quickly,

not as yet had a separate gauge on it but may well do if the issue persists after the change back to Porsche filters,

fingers crossed it does the job.

thanks for the input

NP993

Is the car running hotter than before? The hotter the engine temps, the lower the oil pressure.

sadman

hi,

engine temp and temp when the thermostat open is the same as far as I can tell,

it is unusually hot here but the engine always got hotter than the ambient temp so I cant see that having any great effect.

I have been told that unless the oil light comes on when on tick over the oil pressure is ok ?

any idea if this is correct

EckFe1

Possibly a bad check valve in one of the filters? Would mean that the oil doesn't stay in the filter.
I used to run OEM Porsche filters and changed to Mahle since the last oil change but no change in oil pressure as far as I can tell.
I also use Castrol Edge 20w60 full synthetic. It's thicker and more recommended for air cooled motors.
Hope you find your problem soon, if it is one in the first place.
Ed

Steve Weiner-Rennsport Systems

All we use are Mahle filters with no issues for 20+ years (and we use a LOT of them); still,...its possible you received a faulty one. I would certainly try replacing them, one at a time, to isolate the problem.

Assuming you used the exact same brand of 10w-40 oil, that's not the problem here, however I'd recommend using a 15w-40 in an air-cooled engine unless the outside air temps are below 0 deg C. Generally speaking, 10w-40's are a little too thin when cold and you can see low pressure readings as well as an occasional warnings in the lamp.

IXLR8

+1 ... the surest way to know what is going on.

A new filter does not restrict and if it did, the bypass would open.

As far as I know, the Mahle oil filters, at least the ones I have that are marked Made in Austria, are made for Porsche. They looked 100% identical.

Mike J

I would also consider putting in a fan bypass to keep your temperatures down ; it runs the fan in the oil cooler at high speed all the time. That should help keep the oil temp manageable - .

http://www.pcarworkshop.com/index.ph...verride_Switch

Also, as others have said, if suddenly after an oil change the oil pressure drops, it's very likely something you changed.

So, if you changed the filters and oil, it has to be something there. Did you change the brand or weight of the oil you used?

If you used Porsche filters before and changed to Mahle (which should be good) definitely change those out as suggested.

I am assuming you did nothing else that may have impacted the change, correct?

Cheers,

Mike

IXLR8

For your info, Porsche specs for oil pressure at 80 to 90°C (176 to 194°F):

At idle: 2.0 to 2.5 bar
At 2500 RPM: above 5 bar.

This pic taken off the net...


I get the above indications running Mobil 1 15W-50.

Is your oil cooler fan switching on? You should be able to hear and feel it on high speed at the temperature (10 o'clock) that you mentioned. Its under the right headlight.
Low speed fan at 110°C (230° F) - Porsche spec.
High speed fan at 115°C (240° F) - based on memory.

sadman

thanks guys,

i will change back to porsche filters just to check,

the oil and filter change are the only things that were done other than rear drop links,

i did put some rubbish super store petrol in her but only a little and have since put high octane back in,

over here in the uk 10/40 is concidered by most to be quite a heavy spec oil,many still run on 0/40,
but i may yet change to 15/40 as my engine with 178,000 will have greater tolerances than on a car with 60,000.

a little worried that 15/40 may not give quite the same level of protection on start up though,

i do have an occasional sticky valve lifter but not a constant issue,happens maybe twice a year,have been planning to replace them for a while,now begging to think that if oil is seeping past the seals in a few of these it will also lower the oil pressure,

many thanks for you help and advice

Mike J

I think the amount of oil that would leak past the O rings in the lifters (and at that mileage I would guarantee that no O rings exist anymore.. ) would not impact the oil pressure significantly. Remember you have sprayers and a whole host of other places with oil that "leak". Given it changed on the oil change, that is the likely culprit...

Best of luck!

Cheers,

Mike