fbgh2o

Despite assurances otherwise, I remain concerned that my car suffers from low oil pressure for some reason.

Key facts:

• 1999 C4 with 3.4L engine. Engine was replaced 25K miles ago (30 months) by previous owner with a factory remanufactured one
• Oil = Castrol 5W40 Synthetic
• Pressure Sender was replaced in January
• Gauge reads low by about 0.3 bar (engine off, ignition on it reads below the zero bar)

Here is what I see (I have corrected for the gauge error)

• Cold start up - 4.4 bars - never higher
• Idle @ 180F - 1.1 to 1.3 bars (never any evidence of a warning light)
• 2800 rpm @ 180F - 3.3 bar (typical highway speed)
• 4500 rpm @ 180F - 4.1 bar

I am aware that the owner's manual states at temperature 3.5bar @ 5000 rpm is normal. However, many of the members appear to have pressure above 4 bar all of the time except at idle, so my numbers concern me.

Does it sound perhaps the pressure relief valve is sticking or perhaps there is an obstruction in the oil pick-up?

Your advice and thoughts would be much appreciated

Torontoworker

I think I would start with the gauge, then check connections all the way back to the sender. Pull the two wires off the sender and clean the contacts and then replace and see if there is a change. Your not way off the numbers which leads me to believe it's a 'contact' thing or gauge. The sender usually works or fails - not much in between from what I've read. Most fail high when you power up as mine did or some sit dead at zero or a bit below.

The oil pressure system is about the same and if a pump shaft fails the low pressure light should come on and stay on and your key should be OFF if that ever happens! Then the next sound I would hear is the EMT guy shouting 'CLEAR' as he shock's my heart with those electric paddles if this ever happened to me while driving!

I use the 0/40 myself as the oil does double duty as it is also used as a hydraulic fluid for various operations such as the vario cam system. Lots of controversies over oil around here - no one wants a flame war over it but it's a bit cooler in Bytown then Hogtown and the zero weight has better properties on cold start up conditions then the 5 weight. I know the Mobil 1 0/40 is a lot more money but I think it's worth the cost.

Van

Fergus, that's pretty close to what I get (and I just replaced my sending unit). However, on cold start up, I get 5 bar. Once it's warmed up, and I've romped on it a little (street driving) it's about 1 bar at idle, and then about 3 bar at 3k RPM and 4 bar at 4k RPM or higher.

I'm using Mobil 1 0-40.

Dave!

The running temp. pressure are just fine, but the cold start being 4.4 isn't right at all--I've never had a pressure less than 5 at cold start. It being 4.4 means it's probably something electrical. I wonder if maybe your new pressure sender has a resistor in it that's too high or too low, something weird like that.

fbgh2o

The original and replacement sender behave the same way, both were OEM part parts. So I doubt it's that. Will recheck contacts. I know the previous owner replaced the faces at one point, could that screw up the electricals in the gauge itself?

fpb111

Fergus check it with a mechanical gauge. That way you can eliminate the fear of it being the engine and concentrate on the sending unit\harness\gauge. . If the PO changed gauge faces the gauge face may be misaligned.

fbgh2o

Thanks Frank.

redridge

its the oil.... I use 15w-50. Always get good pressure. 5 bars cold, 4.5 hot, idle 3+.

Van

ivangene

+1 for Ferd...

OP - pick a better oil IMO
I used Q horse power (formerly Shell Helix Ultra) 5/40 (or was it 10/40... forget)

nothing against Castro... but try something else... might be the simple fix - check level... dont overfill. I ran mine about 1/2 way on the electronic level guage not more... and dont FREAk if its low one day... tomorrow it might pop up a bar or 2....also remove the oil filler cap while running and see how the motor runs... rough, really rough... smooth? might indicate some internal pressure/vacuum issue

fpb111

Fergus,
Just got back from a run on back roads and some highway.
2003 C2 Cab 42k mi temp middle of the "0" of the 180 - Mobile 0-40
850 rpm 1.4
2k 2.6
3k 3.8
4k 4.2
above 4k stayed ~4.4
It looks like my pressure relief opens at ~ 4.4 - 4.5

At cold start I can get it to 5 bar. As soon as it starts to warm up it settles at 4.5 when I rev it.

I have to smile with a 2.7ltr engine you were ecstatic if you had enough pressure to keep your oil warning light from flickering at idle. That was with 20-50 oil.

Torontoworker

I'm smiling at this quote as my brother in law with the 77 targa (2.7CSI) says the same thing - he thinks newish P Car owners are spoiled! Ok, we are.

Pac996

First thing I thought when I bought my car was the oil was too light since the pressure reading wasn't high enough for my liking. Had porsche do an oil change to the 15-50 and inspection and I just look back at the light stuff as a second break in oil for the car at 100k miles.

fbgh2o

Ed, have tried Mobil 1 0W40 and Castrol 4W40 with similar results. So I think that oil itself is eliminated. Will check the internal vacuum you described.

Thanks Frank. I am not far off of that except at idle, so it provides some comfort.

ivangene

If its low now (and temps are low) in the summer they will drop farther.

Hope its a mis-read. But you should no guess. Good job in being pre-empted in your work