On a recent trip to the Bay area, something strange happened.

Fresh oil change and filter

ZX pump with maybe 10 hours on it

Sending unit has maybe 10 hours on it

Gauge always real consistent...moves quickly and easily to expected levels depending on driving conditions...about 1/4 up at idle, slightly under mid-way at most driving, slightly above half to 3/4 at 4-5r's...

Cruising up the 101 at a sustained 90-95 mph. Not much traffic so it was going solid at 42, 4300 rpm for upwards of an hour. Oil pressure ran at it's usual slightly above half-way for an hour and then started dropping slowly. Over a span of 15 minutes or so I watched it fall to below the 1/4 position on the gauge! This is all without dropping below 4000! Temperature and all other gauges normal. I was really getting nervous and pulled in for lunch.

After lunch, I checked the oil and found it completely 100%. Exactly the level it had been upon leaving my garage.

What happened?

steve77

Bad Sensor?

The Z's are notorious for having bad sensors both temp and oil.

If the oil did in fact foam up, then I would suspect water or something in there, but just dropping oil pressure...I'm not sure what it could be. Then again, I admit I'm not a grease monkey.

2¢

What brand oil did you use? First thing I thought when I saw this post was that your useing Penzoil. I have never had Pennz in an engine and not seen it foam up. I hate that crap. I'd use $49 per quart Wal-Mart oil over that junk. If you are useing Pennz, I'd switch it as fast as possible...If not, I would assume its just a faulty sender. Try getting a cheap mechanical oil pressure guage for a while and see what it shows for pressure.

Castrol GT 20-50

steve77

OH MY GOD!!!!

Just kidding Zvo...

The diaphram in my stock guage was bad and it behaved similar, I switched over to a mechanical guage and it reads steady...About 60 at a run...I can attach pics of the placement inside the cockpit if u like, lemme know....

How did it do on the ride back?

You stated you were cruising for an hour @ 90 MPH, 4200 RPM.

My Guess is the oil heated up, thinned out, with an expected drop in oil pres. After it cooled down, I bet your oil pres. came back up. I've seen this on the dyno many times. Try a straight 40 wt. racing oil. This will tend to foam less, and thin down less than a multi-grade, street blend.

Phred

That does sound like a possibility. I wondered if that was not the cause when I first read this.. I only wondered why it took an hour. But I guess the heat could slowly climb. Are you running an oil cooler.

No oil cooler.

The ride back was plagued with traffic and CHP officers, so never did another sustained run, although a Civic and I did a little 120 for a minute...

steve77

One hour at 90mph? Didn't you post on the thread about street racing not being a good thing? Shame on you. :devious: :cross-eye

If you are going to run hard for extended periods of time, or run in very hot conditions, it might be a good option to check out.

If the oil was foaming, and you haven't replaced the oil pump, I would say that is the most likey suspect. Probably has a little galling or pitting on the pump rotor or maybe has a little too much clearance due to wear. This could be the cause of a little cavitation in the pump, hence foaming in the oil. A new oil pump is not too expensive, and would be cheap insurance. I personally always use the high volume pump for a little added security.