Hi guys. I've got an 01 996tt with 77k miles on it. Recently, it gave me a heart attack when I noticed oil pressure under 1 bar at idle, and that peak (hot) pressure seems to stop at about 3.5 bar now...

Before, the car would peg 5 bar when cold and IIRC, also at high rpm when hot.

My oil pressure is also a bit unstable, it will randomly jump up .5 bar or so at idle- sometimes dipping down really low, then jumping back up a bit.

I figured it could be a sender, although it wasn't exhibiting the on/off characteristics that those usually do. It was cheap enough so I threw one in tonight. That didn't do anything, so I also pulled off the oil filter cap- my filter was in correctly and was not crushed or anything else. I pulled open the folds of this filter and inspected the contents- I don't see really ~any debris. The oil was changed about a month ago. It has 10w-40 in it- should be thick enough for decent oil pressure even with the heat.

Sooo- that leaves me with what to do next. I did a little more research- it seems that an engine failure is unlikely- it sounds good, no tappet noise, and there is no debris in the filter. Likewise, it appears the oil pumps are very reliable. I see on some parts diagrams there are two pressure relief valves in the case. Googling mostly resulted in failed ones on regular M96 3.4L engines, but not on the 3.6. Nevertheless, I'm thinking about pulling out the PRV's and inspecting / replacing the pistons and springs.

What do you guys think?

By the way, it hasn't gotten low enough that the low oil pressure light has come on- but it has gotten damn low. I could have sworn I saw the needle sit on dead 0 one time at a light the day I noticed this...

 

gotta say. your post isn't entirely clear? but if i had to guess.. i'd concur with your assessment of a failing oil sender unit. esp if it's bouncing randomly, seemingly inconsistently with engine rpm etc. it's all too common.

 

+1 check the wire/connector and replace sender if not wire issue. I believe the sender is right behind the oil filter housing. It's a common issue so start there.

 

that's gotta be the scariest gauge in the cluster, esp when it goes south. after re-reading the op's post. but if you've replaced it already..? strange.

 

Find a location to install a pressures gauge and get a real number I'm sure someone will chime in with better info.

 

No better info than that. Getting some real pressure numbers vs. relying upon that idiot light of a pressure gage is the best idea.

 

i agree. the whole idea of one of the cars most important gauges being electronic.. and known to bug out...is, well.. disconcerting, at best. esp when its failing. i wouldn't want to drive the car. it's not like a voltage gauge or engine temp. it's only our..OIL PRESSURE

 

I use to add oil ps and voltage meters to all my older rides a real pressure gauge would be nice in a car this expensive .

 

Sorry, that was poorly written. I already changed the sender- it made no difference. So, I'm fairly certain I do have a real low oil pressure situation. Other then something odd, I would think an electrical failure is going to fail it to either all the way up, or all the way down... (Open, or closed circuit)

I am not quite sure where I can measure the oil pressure. I could take my old sender and chop it up and make a port / extension to put a real hose on it. That said, it's about an hour worth of labor each way to get in to where the sender is. Only other place that I think is going to be remotely accessible would be the banjo bolt on the top of each turbocharger. That's not gonna be easy either.

I'm probably going to pull the pressure relief valve guts out and check the spring and piston. I might even just replace the spring at $4 or so. If it's not that, I'm really not sure what it would be. I could pull the feed off the case and check the pump rotors for damage, but I don't have any metal in the filter so that would be strange.

 

So, a little update...

I got a new piston, spring, and plug etc for the oil pressure relief valve. No change- nothing looked wrong with the old parts either.

I will probably pull out the oil safety valve spring and piston etc next time I jack it up, just to check that.

I think at this point we are going to figure out how to get a mechanical oil pressure gauge on it somewhere. Anybody have any suggestions for easy places to do that. I can adapt to the sender port pretty easily, but it's not exactly quick to get to.

Cheers,

Pete

 

I have this exact same problem, not sure what to do.

My gauge and sender are accurate, pressure relief valve springs have been replaced, still low pressure.

I have been told the engine needs to be stripped down and inspected to find the problem.

Has anyone fixed this problem before?

 

I would change oild and check for metal in oil filter. My first suspicion is if wire, terminals and sending unit are confirmed good then I would suspect a cluster before the oil pressure. Clusters fail. But also don't drive until you get to the bottom of it.

 

Had a similar issue - needle would randomly bounce from 0 back to 5 and eventually stopped giving any reading at all. Turns out the little wire on top of the sending unit wasn't making a good connection. I pushed it down securely and issue was resolved. I would take another look at the connection, make sure that female piece on the wire is crimped tight enough to make a good connection with the sender male piece.

 

Oil and filter has been replaced, no metal at all. Manual pressure gauge has been plugged in and confirms low pressure when the oil is hot.

I don't know anything about the clusters, are they easily diagnosed if they fail?

 

Thanks Stephen, lets say I have low compression or a blow by issue, sounds like an engine rebuild would be required. I have been quoted $30K from my workshop that has done all my servicing for the last few years .

I think I would just buy a 2nd hand engine for $12k rather than rebuild my existing engine for $30K