Porsche Enthusiasts Club Forum

Hello all,

First time poster, long time lurker.

My recently purchased 86' 2.5 Lux has just started giving me some issues with oil pressure. To begin with, I believe the oil pressure sender unit is incorrect (eg. gives a reading of 1 bar when the correct spec would show 2 bar, 1.5 bar when it is 3 bar, 2 bar when it's actually 4 bar etc...) so bare this in mind when reading the points below.

When I start the car from cold the oil pressure gauge reads 2-2.5. It then settles to 1.5 having warmed up and driven a little. Typically after a few more miles and revs the pressure gauge drops to 1 or less and the warning lights come on.

Prior to a 2 week lay up the oil pressure would hold at 1.5 and barely move, I never saw the oil pressure warning lights before the lay up. I've been taking the car out for small runs to see if it would clear up with more use, but the pressure is still falling to 1 or below with the warning lights on every time.

I've read through a number of threads here with similar issues and I suspect the oil pressure release valve (OPRV) may be sticking. I have a small oil leak from that approximate area of the engine bay as well. Does the OPRV sound like the culprit given the symptoms? I think the OPRV is original although I believe it has had the seals refreshed not too long ago.

Other than changing the sender unit to the correct spec and looking to confirm the pressure is actually ok, is there anything else you can recommend I look into? I'm not hearing any unusual/new noises from the engine bay (tappets aren't noisy to my ears).

Cheers

Hi

A few things....which oil are you using? these cars don't like modern thin oils, you mention that the OPRV has had new seals fitted recently, who did this and did they use the 'alignment' tool to ensure the valve is positioned correctly? These valves are very expensive but also very reliable, my car is still on it's original (209k) although it has been stripped down and refitted with new seals. Oil pressures can vary in 944's, there can be a number of reasons for this, oil as stated, worn engine bearings, worn or loose oil pump/silicone crank seal, bad OPRV. Now according to Porsche, any reading above 0.5 bar is ok, personally, I'd disagree with this but what is bad is when the pressure has dropped to less than what it normally shows as you seem to be referring too. A cold engine should give a reading of 4-5 bar at idle and once warm no lower than 2, most important, no matter what the normal reading is that once the revs are raised the pressure shoots up to more than 4 Bar, hot or cold. A further possibility is a loose crank pulley as this would reduce pressure on the pump/crank seal and thus lose oil pressure, the pump is driven by this small silicone seal and relies on the correct torquing of said bolt to run properly. IIRC the pulley is torqued up to something like 150lb, despite this, there are many reports of crank pulleys working lose, I've had it happen to my own car, I suspect it may be due to a resonance from worn alternator and A/C compressor bearings which are also run by the crank pulley on one belt. The oil pumps themselves are nye on bulletproof, very unlikely to be a failed oil pump. It's also worth cleaning the OPRV electrical contacts, especially if as you say you have oil leaking from that area and perhaps check the gauge contacts in the cluster too. Lot's of things to check.

good luck

Pete

edit: oh and welcome to the forum..

Thanks Pete.

I know the OPRV was aligned properly with the tool as the previous owner had a thread here documenting it (I know he is thorough in his work)

Since purchasing the car I have topped up the oil with 500ml of 10w/40 semi synthetic oil. The car has done 142k miles so I suspect going thicker will help at the next change.

Will try and get the car raised properly to have a better look at the area oil is gently/lightly leaking from. The leak has not increased/deteriorated since I purchased the car and the drop in oil pressure has only recently developed.

I did some issues with engine cooling due to a leaking radiator. I'm wondering if the short run I had with a rapidly heating (but not overheated) engine might have caused this oil issue? Too much of a coincidence?

thanks
David

Hi David

Try a thicker oil, I use Mobil 1 10w-60 motorsport ( not the extended life oil with the same multigrade figures) in my car and that's with a fully rebuilt engine with approx 14k clocked so far. A 10w-40 is IMHO too low for our cars in the UK climate, especially when we have a hot summer, yes I know that's rare and we are currently heading for winter but if you check your handbook (assuming you have one) for our climate you need when talking multigrade, 20w-50 or 15w-50, this will cover you for -10 to +40 Fahrenheit or -15 to +40 respectively. I used to use 15w-50 but Mobil stopped producing this in the 'motorsport' series which I prefer for my own car when considering the mods implemented. A 10w-40 isn't going to harm your engine, it fulls within Porsche spec but as these cars get older and with higher mileage, it's best to use something a little thicker to run in those now larger gaps from worn bearings etc.
Change the oil often, these cars like fresh oil, please do check the crank pulley torque asap, you don't want this to full off as mine did 7 years ago, it can cause severe damage to the engine, read the book, got the T-shirt so to speak. As a piece of info, when I had my issue with the pulley the oil pressure dropped from it's usual 5 BAR on idle when cold to barely above 2 BAR and so I knew that I had to do a complete rebuild, note that this reading is similar what yours is showing now so I hope that it's related to other things, OPRV, crank pulley or just dirty contacts.....

Good luck sir

Pete

edit: Forgot to say, when my pulley fell off I had for a few weeks before noticed a slight drop in oil pressure, this is why I say to anyone today experiencing a drop in pressure to check the crank pulley...

Possibly oil pickup pipe strainer clogged up or even a cracked / holed oil pickup pipe.

Good shout Glenn, usually we give advice from our own experiences, I've never had a problem with the oil pickup but then believe this to be mainly when used on the track, something my car has never taken part in. David stated that the previous owner is of this parish so one would assume a good custodian of the car and thus a clogged strainer unlikely but did he use the car on the track?

Pete

I know personally, through knowing the owner, of 1 944 S2 cab which had never been tracked and has suffered a failed oil pickup pipe. I am also aware, again through knowing the owner, of a well maintained 944 turbo (220) which had a clogged pickup strainer resulting in low oil pressure that he "fixed" by using thicker oil until the real cause was discovered and the problem rectified.

Track use or poor maintenance is not necessarily in play for either of those scenarios, although hard use may exacerbate the problems

Given that the labour required to access the oil pickup pipe is not insignificant (I believe Clark's gives it as 8-10 hours) I'd investigate other more accessible causes first!

Just for the record, my S2 runs on 10w40 semi and gives "text-book" oil pressure readings.

Thanks Glenn & Pete

The car has not been tracked as far as I am aware. I've ordered a new sender unit that is correctly rated as it feels like any diagnosis work is going to be a shot in the dark until then.

I had the car out over the weekend for a short motorway run and it held good oil pressure to begin with; starting around 4 bar before dropping to 3 bar when warmed up (or 2 bar and 1.5 bar given my sender unit). Pressure rose as the revs picked up and it seemed to be quite happy.

It was only once I had come to a complete standstill at a junction to turn back that the pressure fell and the warning light came on at 1 bar (this would mean the pressure was 2 bar given my sender unit). On the way home pressure picked up enough under acceleration for the warning lights to go off (would perhaps have gone up to 2.5 or 3 bar with the correct sender unit) but would fall back again when cruising or with my foot complete off the accelerator.

As a precaution I am not going to use the car until the sender is replaced and I can confirm the readings. If the pressure is staying within the range of 2 to 4 bar then i'll be a bit more relaxed about it. If it's heading down to 1.5 or lower then I'll be more concerned.

Is the crank pulley bolt tight? 150lbs/ft

i haven't had a chance to work on the car this weekend.

Before tackling the crank bolt I assume I need to lock the flywheel. Do I have to remove the starter motor to get at it or is there an easier way?

Yeah, starter off, but you don't have to disconnect it if I remember rightly - think you can hang it out the way with some wire/bungees.

Buy a flywheel lock tool to jam the ring gear. I got a Draper 'universal' one which works but it's a bit fiddly. There are 944 specific ones out there - think Arnnworx might do one. Don't rely on the 'jam flat blade screwdriver' method, the crank bolt needs to be seriously tight. 210Nm springs to mind, but double check.

Good luck

Yup 150lb/ft

This is the one I was thinking of:
http://www.arnnworx.com/catalog/index.p ... cts_id=183

Or alternative European supplier:
https://m.ebay.co.uk/itm/For-Porsche-92 ... Ciid%253A2

I'd be tempted to buy the locking tool from the OPC. I'm sure I only paid £35 last year.

Personally I wouldn't be running the car at all until I was happy I'd solved the problem or identified a faulty sensor. Replacing all the crank and big end bearings is not a job of 5 minutes.

Good luck with it and let us know how you get on.

BR

Matt

Finally got the new sender unit fitted and the crank bolt torqued and took the car out for a test run.

Oil pressure looked good the entire time. Fired up & it immediately sat at 4bar, climbed to 4.5 under acceleration, stayed at 4 when cruising and sat at 3 when stationary.

Thanks for your help all. Much appreciated.