Alan Cesar Associate Editor
March 23, 2012 10:55 a.m.

I recently started driving a bit of distance to work. 80 mph interstate (~4k rpm) for about half an hour. I also did an engine rebuild ~1 year/10k miles ago. Right now I'm about halfway to due for an oil change. For the record, interstate speed limit is 70 here. And this is a '91 Miata.

My oil pressure is doing some strange things. It was running lower than before on the highway, and I'd see lower than normal pressures at idle after the interstate stretch. That's compared to the readings I'd been seeing in the time since the rebuild. So, 30psi at 4k rpm, just under 15 at idle.

But the needle also floats a bit. It'll fluctuate up and down by a small amount.

Today it got extra weird. I was cruising at slower speeds (say, 65-70 mph indicated). The pressure did some occasional jumping—not just floating—from ~30 to what I'm used to (~45) and back. At idle, it would jump from nearly zero (!!!) to 15-20 psi. That freaked me out a bit, but the sound of the engine hasn't changed and the way the needle was jumping made me think it was electrical. I got to work safely (another 15 minutes of driving).

Oil level is OK. I'm going to clean the terminal soon and see if the problem returns.

Anyone experienced this weirdness? If that pressure continues to drop like this with a clean terminal, where do I look next? Is it time to change the sensor, or look into deeper issues?

Per Schroeder Technical Editor/Advertising Director
March 23, 2012 11:01 a.m.

If it's a quick flicker on the gauge, it's usually a ground issue...

spritedriver28 New Reader
March 23, 2012 11:08 a.m.

Pull the wire off of the sending unit (under the intake), clean it and smear on some dielectric grease. If that doesn't fix it the sending unit may be wonky.

Keith MegaDork
March 23, 2012 11:24 a.m.

Yup, that's where I'd start. The terminals corrode, and sometimes the sending units clog up over time.

Xceler8x UltraDork
March 23, 2012 11:28 a.m.

I'm with the "it's a ground issue" guys. Sounds like you either have a wonky sending unit or a ground issue. Intermittent ground issues can act this way as the sending unit gains and loses contact.

If you clean the ground and make sure it's tight...and the issue persists....What model is your Miata? Early Miata's had an oil sending unit that can pick up spark knock and blip. It's usually a really fast flick as opposed to any reading with longer than 1 - 3 second duration.

Woody UltimaDork
March 23, 2012 12:22 p.m.
spritedriver28 wrote: Pull the wire off of the sending unit (under the intake), clean it and smear on some dielectric grease. If that doesn't fix it the sending unit may be wonky.

It may be easiest to access if you remove the passenger's side front wheel and go in through the wheel well.

PseudoSport HalfDork
March 23, 2012 1:59 p.m.

In reply to Alan Cesar:

I had the same problem happen to my 91 Miata. On the highway the pressure was jumping around and when I got off the exit and came to a stop it would jump from 0-15 psi. I pulled over but the engine sounded fine so I wiggled the connector on the oil sending unit and my gauge went back to normal.

You'll need to log in to post.

Also on Grassroots Motorsports

Follow Us to the Nürburgring

10 hours ago in News

Follow along as James Clay from BimmerWorld contests his first ADAC Zurich 24-Hour race at the Nürburgring.

Shark Bite: Back in 1997, Hyundai Was Into Rally

11 hours ago in Articles

A Hyundai Tiburon as a rally car?

From the GRM Vault: Our First Drive of the Original BMW M3

1 day ago in Articles

We tested BMW's E30-chassis M3 back in 1989. Here's what we thought.

Great Moments in $2000 Challenge History: Minor Gasser

1 day ago in Articles

Here's what happens when you put a Chevy 350 in a Morris Minor.

What’s the Soonest That You Have Raced Your New Purchase?

1 day ago in News

This BMW M3 was wearing numbers 24 hours after getting registered.

You Need This: 2005 Lotus Elise

2 days ago in News

A Lotus Elise looks so right in British Racing Green.

2017 Mazda MX-5 RF

2 days ago in New Car Reviews

We're big fans of the Mazda MX-5. Now Mazda went and put a retractable fastback on their fourth-generation car. So, ...

Project Ramp Truck: Installing Sound Deadening

2 days ago in Project Cars

Time to cut down on heat and road noise making its way into the cab.

Eric Foss Sets Fastest Time Ever at the Tire Rack Ultimate Track Car Challenge

3 days ago in News

47 of the country's fastest cars battled it out for track supremacy.

Who Wants to Design the Next GRM T-Shirt?

3 days ago in News

Blipshift is involved, so you know that it will be cool.

Reader's Ride of the Week: Improving Upon the Ultimate Driving Machine

3 days ago in News

This E36-chassis M3 just keeps getting better.

What Was the Most Powerful Car at the Grassroots Motorsports Dyno Day?

3 days ago in News

What if we told you it was an Audi?

OUR SPONSORS

Grassroots Motorsports Magazine

Subscribe Today

Also get your instant access to the digital edition of Grassroots Motorsports Magazine!

Learn More
4gQDkngEy9sJThba3TNww9BfaZDA72TF