Been using Motul 5-40 for years. Last change was done w X-Cess, not X-Clean as I seem to recall. Immediately noted high oil pressure, gauge remaining pegged even warm at idle. Was going to change out gauge when I noticed a similar post by fellow user.


Today after about 1000 miles I changed oil and used Mobil 0-40 on a hunch. Oil pressures returned to normal, 5 at startup, 1.5 warm idle, 3-5 on road at rpms. I don't know what this says about Motul XCess or rest of line but I am concerned about effect of excessive oil pressure over time, especially with OEM setup bypassing filter under certain conditions.


Any thoughts?

 

If you're ever concerned about the oil gauge reading wrong, turn the car on to accessory mode, don't let the engine turn over. If the gauge reads anything other than zero, the oil pressure sending unit most likely needs to be replaced. Sometimes you can just clean the contacts but that doesn't always work or might only work partially.

 

Good to know. Tx

 

Did this last night. In "off" the needle is at the bottom of the 0 line. In Acc the needle displaces slightly just to the top of same line, maybe +.05 to .1 (one tenth). Is there some minimal pressure in system or would you read this as a 'fail' for the sensor?

 

There is no residual oil pressure after the engine has been off a short time (on the scale of seconds).

I recently (easily) replaced the oil pressure sender on my 2005 C2S. I was alerted to its failure with the "off" test described above and the abnormal unexplained variation in oil pressures while the engine was at various RPMs.

 

OK. On cold motor with motor off, key in right click position I am now seeing a +1 reading on the op gauge. I guess this is the indication of sensor failure. While in general I am not a believer of coincidence I have to think that initial 'problem' and subsequent 'cure' has nothing to do with brand of oil. I will swap out sensor and go back to Motul to see if this holds true. But not for a while. Just laid out 1200$ for coilpacks, plugs, service and need a break.


Thanks for help.

 

I don't know if this helps the "coincidence" part but my oil pressure sender seemed to fail "overnight" - meaning, it was seemingly working one day and the next day I noticed the quirks, and the next, next day the quirks were worse and then leveled off at a point where I told myself I just couldn't trust the pressure readings anymore.

I've read ulcer-causing stories where the sender failed in the "other" direction - reading no pressure at highway speeds, and the driver then having to make a semi-emergency pull-over to minimize blowing the engine and then a tow - to then find out it was just a bad sender.

 

The oil pressure sender went bad in my 06 at 26K miles.

 

Oil pressure was ok, changed oil from X-clean to X-cess: reading too high. Rechanged oil to M1 and back to normal. You gotta admit the odds are poor. But you're right. At least I didn't need to call a tow truck. Kind of weird though no?

 

I found when I just stick with Mobil 1 0W-40 my cars run better

 

UPDATE: I Did NOT change out the sensor. After 2 weeks using 0-40 Mobil the o p gauge readings continue to be perfect from idle to full throttle. Hot to warm idle 1.2-1.5, warm over 3500 4-5. Cold 5. I have to conclude the problem was with the viscosity of the batch of Motul 5-40 Excess. I have been recommending this oil. I can no longer do so. Idk what the effect of excessive oil pressure is over time but it can't be a good thing.

 

Hey Gpjli. I think I stumbled into the answer for you.

Take a look at the post from Flat 6 Innovations on the following thread posted on Rennlist (He means Motul instead of Mogul when it is first mentioned). The bottom line is that he is saying that Motul does not mix properly with other oils unless the previous oil is fully flushed out first. According to others the two oils are not "miscible". There is always some leftover oil during a change... Flat 6 says around a half quart and some claiming that it is a couple of quarts (I find this harder to believe) or so regardless of how long you let it drain. I assume this mismatch caused the problem you saw and possibly caused the "mixture" you ended up with to effectively thicken beyond its intended specs. Hopefully you won't still have some degree of that problem now that you've switched back since there may still be some Motul lurking about.

BTW, thanks for this thread. I was considering Motul the next time. That plan is now aborted!

Here is the link:
http://rennlist.com/forums/997-forum...ange-3.html#40

 

Note I had been using Motul for several years before this incident. Different scenario. I always got good pressure readings maybe .5 bar higher than w M1, ie 2 at hot idle. This time the change was from 5-40 X-clean to 5-40 X-cess which should not be a problem. Same foundation for both oils and both are on P list. When I switched from M1 to Motul 5 or 6 changes ago there was no issue so I'm thinking that's not whats going on I'd call them but I tried once before on a usage issue and they hung up on me. Maybe Redline is in my future We'll see. I'm good for the next 6 months in any case.

 

I use Motul 8100 xcess every time. Never a problem with high oil pressure.

 

OP tested the oil pressure sending unit while the car was off and it registered pressure. Now supposedly it doesn't. Whether there's no oil, too much oil, or mixed oil, that sending unit should still read zero. My guess is his sending unit is on the way out or the contact is poor and being affected by seasonal changes.

Before I had mine replaced, my readings changes depending on temperature, relative humidity, and even me just playing with the contacts. Taking them off and cleaning them resulted in a lower reading but not a perfect reading.