Hey, lot. I've searched a little and found a few things regarding low oil pressure that involved either the sender, the thermopellet, or the front cover o-ring, but nobody's situation was more than vaguely like my problem.

I of course get high oil pressure on a cold start. It has been especially cold for north FL these past few days with the storm, and I have seen my oil pressure dwindle down to around or just above 0psi while driving. Sometimes it will jolt back up to 80psi and fall back down to around 60 psi which I considered normal, although it doesn't usually ride past that even at ~8k. Sometimes it didn't go back up until I put it in neutral to slow down and would go up to 20-30psi. Warm idle has always kinda been low as well at around 15psi, sometimes lower.

In preparation for this cold and my FC being the daily, I put a little bit of 10w-40 in a few days ago in hopes to raise the pressure a little with the thicker oil. I got my usual oil, just 10w-40 and it did make a slight difference until it started doing this two days ago.

I guess my question is which of those three things could it most likely be? I mean, it seems intermittent for now, but it has been unusually cold for this area the past few days and I wonder if that could be part of the problem too. That's my inner-Floridian coming out. 89, read the sig, oem thermopellet FWIW. I appreciate any help, you guys.

 

You're giving oil pressure readings in psi, do you have an aftermarket gauge?
First thing I'd check would be the sending unit, in any case.

And, while the temps might be unusual for your area, they are surely within the normal range for the car and shouldn't cause the weird readings you see.

 

Check your wiring, the condenser/grounding capacitor. Its a little black box with a tab that mounts, usually, to the clutch slave cylinder. On my '88 the wire broke off the box, periodically grounded, and my gauge gave me wildly varying reading. When it finally stayed grounded it seems to have damaged my gauge.

 

Where can I find the sending unit?

I have previously cleaned up the capacitor end and used a stainless bolt. Anything else besides check the wiring too? I have a UIM project coming up that I will address all of this.

Is the car safe to drive? I mean it might be the gauge but it might not.

 

The sending unit is below the oil filter...one wire connected on the end.
Is the water temp varying as well?
Since the oiling system provides @ a third of the cooling capacity, it would seem that a problem with the oil might be reflected in the water temp.
Assuming there is a real problem (not the wiring/sender) and you have a real temp gauge (the stock S5 won't respond much to temp variation), you might see changes in water temp as well.

Maybe.

Another possibility (however remote) would be an obstruction of the pickup tube/strainer in the pan.

 

Unfortunately I don't have any aftermarket gauges. I have been highly considering getting a mechanical oil pressure gauge and a linear water temp gauge so I don't have to guess at things like that any more. I don't have a need for a pillar pod or dash mounted gauges yet so I'd want those to go in the cluster in the factory spots. Is that feasible? Can I use silly AutoZone gauges or do I need something better?

With the sending unit, what am I looking for? I just need everything to be nice and clean? Good contact at the sliding connection I've read about?

I haven't had to reseal the oil pan since I built it, but it seemingly drips slowly. Maybe a drop every 3-4 days. I always check my oil before I drive, warm or not and it's definitely not losing oil, and I'm not burning any more than I should; at least there is an absence of smoke. I haven't any clue what could be blocking the pickup.

 

I started having a similar issue with my gauge a month ago. My issue is the sending unit considering everything else is normal. I didn't test the oil pressure with a mechanical gauge, but if it really had no oil pressure at times, the engine would be clattering like a banshee.

 

Get some VDO Vision series gauges. They are electric (much easier to install than mechanical), good quality yet inexpensive. Check egauges.com.

I suppose they could be integrated into the stock cluster but I've deleted the cluster altogether, so I'm not sure what would be involved.

Nor do I.
I was simply casting about for a explanation of your symptoms.

 

clean the sending unit connector or replace it with an aftermarket unit. the problem is usually oil and dirt on the sending unit connector which breaks the connection intermittently or a faulty sender unit itself.

 

That connection on the op sending unit is the most harebrained thing ever.
No other connector is like that (that I can think of) and I see no advantage to it, so the whole thing seems just arbitrarily shitty.

And yes, sending units wear out just like everything else and that could be the case here.
If the op does in fact get new gauges, the (required) new sending unit would solve that problem right away.

 

but i'm not a huge fan of redundant gauges, fixing the problem with the OE gauge usually costs less than replacing it with another gauge cluttering up the interior of the car.

the connector design is bad but the problem isn't so much the connection design but the fact that the oil filter sits right on top of the unit, leaking oil onto it during oil changes and fouling the connection sooner or later. the slip on design is very very old and still was used until recently on many truck engines, but the only real fault is the sensor location.

 

I just installed AEM mechanical gauges for both oil temp and pressure. There was quite a bit of difference between the factory xdcr and AEM pressure gauge. In my case about 20 psi.

 

Ben hit the nail on the head. Cleaned it a bit and works fine. I agree it's in an awfully ridiculous place underneath the pedestal. Ben, I'll also have a look at those gauges. The reason why I want to integrate into the cluster is for the very sake of not having a cluttered dash, plus I don't want to block my idiot lights. Hah

jdonell, nice gauges!

 

Could the "condenser/grounding capacitor" affect the reading of the gauge?

 

I like your reasoning.
Before I swapped to the Miata cluster I looked into doing just what you propose but decided it wasn't worth it. There are several obstacles to overcome, worst of which is the paired diffusers and faces. It's not like you have individual gauges in there that can be popped out and replaced, they all share structure/mounting...you'll see when you disassemble the cluster.
I was able to substitute VDO gauges into the Miata cluster with little difficulty.

No, it's a safety measure to protect the gauge in case of voltage spikes.
As long as that wire is properly capped off and not grounded the readings will be normal.
Lots of FCs are missing that condenser.

 

Thanks

 

without the condensor if the wire is shorted out the gauge will fry, it only takes a few seconds to burn out the oil pressure gauge in that event and i have seen it happen.

 

Note taken to see about a Miata cluster. Plus it's even better if the Miata cluster fits inside our shrouds with ease and still looks good. I really like my rpm gauge showing 8000 as redline though. Hahah. I do also wonder if the clusters have revs in the centre.