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996 Oil Pressure

T

tykes

PCGB Member
Member
Would appreciate a little advice from the tech gurus on what appears to be a problem with my 996 C4 Cab Tip. The car is a 99 with 60k on the clock. Should also point out that I live in Dubai! Whilst this is my first post I am not new to 911's as I also have a 993 Targa in UK and have had several others but mainly aircooled variants.
The issue is this:
On start up from cold (bearing in mind ambient temps here)oil pressure is at top of scale.
Within 5 minutes it starts to drop and at 2500rpm is down around 2.5.
When fully warm at idle it barely registers although at 5000rpm it climbs to 3.
I had it checked out by the local Porsche garage who changed the sensor and claimed everything was fine.
I am not so sure!
There are no unusual sounds from the engine and it does not use or leak oil. In fact the car runs very well indeed. I am just freaked out by the sight of the needle being low. My 993 never drops below 2.5 when warm at idle and is at 4+ at motorway speeds when warm.
I haven't plugged an oil pressure gauge into the engine direct and that may be the most sensible thing to do but is there anything else worth checking before I start thinking about an engine rebuild? I suppose the sender could be faulty or the gauge.

Any thoughts would be appreciated
 
It sounds untypically low to me. What oil are you using? Someone hasn't used a 0W-30 by mistake, have they? I can't see the ambient temperature would make a huge difference to the hot oil pressure. After all, it is water cooled! You should see about 1.0-1.5 bar at hot tickover, and 4.0-5.0 at 5000rpm.
 
Thanks Richard - that's a good point! When they changed the sensor they also changed the oil and filter and used Mobil 1 but not sure of the viscosity. I will check - what viscosity is recommended? It is the speed at which the pressure appears to drop that has me concerned especially after being high on start. If I had bearing or pump issues I would have expected a more gradual deterioration. Is there a filter in the pump that might be clogged? The car does not overheat at all even when temps are in the 40's and in traffic. Thanks
 
It should be a 0W-40 or 5W40 for general use. In that environment, I would have thought a 5W-40 would be better, although the pressure you get when "cold" seems to be OK. There is no filter in the pump itself, but there is a pressure relief valve in there, which could cause this problem if the spring has broken. It is reasonably accessible IIRC, so it would only take a short time to change it, and they are less than £5. I would check the oil viscosity first, just in case it is an easy fix.
 
I also have an oil pressure question. Having read various posts and forums, there seems to be plenty on low pressure or errctic prressue, but not a lot on high pressure. Mine is a 99(T), 996 C2 Tip Cabriolet. On start up the pressure is near 5, and after 85C on the temp, is seems to run between 4 and 5 when at motorway speeds 2500-3000rpm. When ideaingl, anywhere between 1.5 and 2 when at 85C on the temp. The oil reads OK, and was changed in april when I bought th car. Having read the manual, it says 3.5 at 5000rpm, mine does not match that, and while it seems to run fine, I have never had a car with a pressure gauge, and just worried in case the pressure is high, and that I will give it some beans and the engine will pop and loss its oil, and I get a massive bill! Thoughts please?
 
I think you will find the 3.5 at 5000 is the minimum you should expect - not the maximum! The figures you quote seem pretty normal to me.
 
Checked the oil and they used Mobil 1 OW-40. Think I will try 5W-40 and see what difference that makes before I have a look at the pressure relief valve. Assume this is located in the sump? Any tips on actually doing this or should I take it to the agents? Many thanks for the help.
 
The oil pump is at the back of the engine, at the bottom. You can see the spring and piston on the diagram (12 & 13). I'm not sure if you can get to it with the engine installed though.
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