2005 350Z with VQ35DE Engine. About 138,000 Miles.

Once the car warms up, at idle at a stoplight for example, the oil pressure gauge sometimes falls to the far left mark & the dummy light comes on. The car does not stall out or anything but it sounds like the typical bad gallery gasket behavior. (Please, NO!) We have it at a shop, and they mechanically tested the oil pressure and installed a new Nissan OEM oil pressure sensor. They say the mechanical pressure test shows that the oil pressure is right where Nissan says it should be. They are still poking around, but they think the problem might be with the waterfall gauge itself. Does this theory hold water?

My question is does the dummy light operate due to input from the dash gauge in the waterfall, or is it receiving the input from the actual sensor. If it's the latter, it would seem their conclusion may be incorrect.

Second, it could be that even the mechanical pressure test is not catching the problem as it happens during actual driving. My limited knowledge would tell me the only way to confirm that would be to hook up a mechanical gauge with a hose long enough to reach inside the car, and monitor the mechanical gauge during actual driving. Is that dumb thinking? Is there some other way?

Finally, another mechanic I use for "bigger" jobs has built a device that may be of interest for those that want a simple way to test oil pressure without the need to remove the sensor and thread in a gauge. He's kind of a mad genius type and he's has built a lot of tools & machines from scratch. Check this out on YouTube and see what you think:


Thanks in advance for any insight.

 

More than likely you have either a faulty sender unit or a faulty stepper motor in the cluster. If their mechanical testing showed good oil pressure then I wouldn't worry about the gallery gaskets. Note: The VQ35DE is not prone to gallery gasket failure like the VQ35HRs. Can it happen? Yes, but it's very rare comparatively. For peace of mind, I would replace the gasket when doing a timing chain service (around 150k mi recommended), this is not something you should be concerned with until then IMO.

The cluster dummy light is most likely activated by the sender unit's signal, not the position of the gauge stepper needle. The cluster stepper motor isn't that intelligent, it simply receives the analog signal and sets the needle gauge accordingly. In short, you most likely have a bad sender unit or potentially faulty wiring/connection to the sender unit. Could the stepper motor be bad? Yes, it's pretty rare, but it can happen. If the needle appears to be sluggish or sticking full low or high, odds are the stepper motor on the cluster is bad.

Well that's my 2c, good luck!
-Icer

 

Thanks for the reply, as always!
They tested the old pressure sensor (is that the same as "sender unit")? and they said it did seem to have a small amount of "leakage" which it sounded like they meant electrical leakage. They also tested the wires to the pressure sensor and they were all OK. They cleaned the connectors, installed the new (OEM) pressure sensor, test drove, etc. About 3-4 hours labor and they were kind and charged me only for one hour. The gauge itself is not jumpy at all, it operates smoothly. The tech said that both the sensor and the gauge contribute to the dummy light, and it is possible for the sensor to be working perfectly, and a bad gauge could set off the dummy light. We'll give it a week or two and see if the problem has gone away. If not, I can pick up a used set of gauges off EBAY and install them and see if it changes anything. Unless it's an easy fix to repair or replace the existing stepper motor that someone would like to explain to me how to do!

 

Hey JSMCO,

If you truly need to, I would simply replace the triple gauge pod cluster, used ones are fairly cheap and easy to install. Make sure to get one from an 03-06, for some reason Nissan changed the multi-display menu in 07-08 and removed the Tire Pressure data. The oil pressure sensor/sending unit is one in the same (terms used interchangeably). There's probably a troubleshooting guide in the FSM covering how the oil pressure warning light is activated (I assume this is what you mean by "dummy light"), but I haven't had the time to dig through and find out. That was very nice of the shop to discount the labor. When they mention leakage at the sending unit, they probably mean the internal seals failed (not uncommon) as opposed to a leak at the threads. When this happens, you will get faulty readings, oil can seep into the harness plug and cause poor electrical contact. Left unchecked, this can turn into a pretty bad oil leak as well. In the end, it's a good thing you caught this and took action. I'm confident the new sending unit will resolve the issue.

Cheers!
-Icer

 

Thanks again for the reply.

Yes, I did use the term "dummy light" for the warning light, correct. We'll test it for a few days and if the gauge now works right, problem solved. If not, as you suggested, next step will be to get a used gauge pod and see if anything changes. If not, then will have to proceed from there.

 

Wanted to circle back on this. It has been a month since the new oil pressure sensor was installed, and the gauge has worked correctly since the install. From the symptoms, I was concerned it may have been the gallery gaskets, as a lot of times, it sounds like a bad sensor will just peg the gauge at max or show no reading at all, but the new sensor seems to have fixed the problem.

Thanks for the input!