am

Hi, i searched on this forum for a similar issue but did'nt find one for a 1970 911T. Here it is, when my engine is cold at 1k rpm the reading on my oil pressure gauge is 4 and at 3k it shows a bit over 6 but when warm at 80 celcius (176 farenheit) at 1k it shows a bit under 2 and at 3k a bit over 2, That's a big difference, is it normal ? i have a new sender unit, could my gauge be dying ?

Steve Weiner-Rennsport Systems

More information is really needed to offer any assistance,...

1) How many miles on the engine?

2) What brand and viscosity oil are you using?

3) Is this a recent development or has the OP always read low to you?

4) What part number is on the new sender?

am

Thank's for helping me.
1- 160 000 kms (100 000miles) from the numbers on the pistons engine redone twice (runs great)

2-Valvoline premium 10w30

3- When i bought the car i brought it back home from a 1800 miles ride, the engine had synthetic oil and it had excatly the same problem.

4- part # from Pelican invoice : 901-741-551-01-M100

The oil tank is not the original oil tank, i think it's from a 1972 or 73. i have K&N air filters so i have one hose from the crank case breather to top of oil tank and one hose from top of oil tank going nowhere (open).
I give you these infos just in case it might help.

Steve Weiner-Rennsport Systems

1) If you have 100K on the lower end of the engine, your rod and main bearings may be simply showing age. As bearings wear, their clearances open up and that manifests itself as lower oil pressure.

2) 10w-30 is too light for air-cooled engines,.............period. You need at LEAST a 15w-40. A 15w-50 or 20w-50 is better for summertime driving.

3) There are two makers of those oil pressure sending units: original Porsche, and Uro (aftermarket). I NEVER use anything but Porsche factory items for these applications so you should see which one you have.


You likely have the '73 oil tank since the '72 one is specific to that one model year, only. All that does is add more capacity and thats a good thing,..

srf506

As stated above, the engine clearences open up as the engine warms up and the oil's viscosity thins as it heats up, so some degradation of the pressure is normal. As long as you have at least 1-bar of pressure per 1000 RPMs (the oil pressure gauge should be at 1 or higher at a 1,000 Rs, 2 or better at 2,000, and etc.) it should be fine. Its an oil-cooled engine, make sure you keep it topped up, and make sure it is functioning properly. If you're not making any smoke on accel/decel or idle it'll last. A small puff on start-up is almost the usual in these motors and if it does that, but then quits smoking right away I wouldn't get excited. Also, its good advice on the oil-weight too. I live in Florida and I only use 20-w50 in my 930. Good luck.

Batman 357

My 82 SC is about it the same boat. Warm idle it's less than 1bar. At RPM it's equal or better 2-2, 3-3 etc. I use Pennzoil 15-40. It has 200k on the odo with a rebuild in it's past. I've only had it about 8 months. Runs well, no visable smoke & starts right up. Uses some oil. Is this a problem.....

Ed Hughes

In my uneducated opinion, 15-40 on a 200K mile 911 in OKC is not a good combination. You should absolutely be running 20-50.

am

Thank's for your precious help,
1- the bearings that show wear have been changed
2- I will change the oil to 20w50
3- how could i know if it is a genuine Porsche sender unit when i look at it ?
i'm thinking forget, it any way i can't see it anymore where it is placed

Batman357 i think low oil pressure is always a problem.

theiceman

Well you have to determine the conditions .. 1 bar of presure ( we will use Bar just for arguments sake ) while running at 5,000 RPM would be low and your done . 1 Bar of pressure while idling on a hot day in bumper to bumper traffic could be nomal . In fact some older cars , even have the oil pressure light illuminating or flickering under these conditions, and this is considered normal . I would say have a compresion and leak down to check the general health of your engine and follow the above guidelines for pressures at RPM , and your good to go ..

am

Thank you guys for your help and sorry for the delay to thank you, i have so many problems to log on this website and have no news back from rennlist
I'm in the range of ''bar'' per 1k rpm or over so nothing much to worry but i'll change my oil to 20w50.
Thank's again