My oil pressure sensor seems to be failing. The current one has been in there for 19 years and worked fine until recently. I have a new one, and the shop manual says apply sealant to the threads, but I seem to recall a Mazda mechanic telling me to just use teflon plumber's tape. I don't remember what I used last time. It never leaked.

Recommendations?

 

Teflon tape here. No leaks, problems.

 

If you bought an OEM Mazda sensor, I believe it should come with sealant applied on the threads.

 

It has about 1/3 of the threads coated with a blue material, but 2/3 of the threads (the ones that go in first) are bare, and since the shop manual says to apply sealant, I figured that the blue stuff was not sufficient.

 

I think Teflon tape is sealant and paste or the tape will work...just be careful not to get any in the opening of the sensor.

 

Loctite has a nice lineup of thread sealant.

 

any of that will work, in fact if you just put it in, it will likely seal.

 

Teflon tape or thread sealant. Don't overtighten it and make sure you clean out any old tape/sealant. I've seen irons crack there.

 

I used oil/gas resistant sealant on mine. I separated the sensor from the adapter, torqued the adapter to the iron per shop manual, then screwed the sensor while holding the adapter with a wrench to prevent overtightening on the iron.

 

Thanks everyone for the thoughtful advice.

Pete

 

My factory pressure sensor doesn't read well either. It was showing scary low values sometimes, so I installed an aftermarket one connected to my aftermarket ECU for logging and failsafe limiters. This video/data overlay shows a quick comparison while the engine is warming up:

I used Permatex High Temperature Thread Sealant from the auto parts store, it's only been a few months but it has worked well so far.

 

Thanks. That OEM oil pressure gauge looks like mine now -- low readings from a failing sender.
That is an amazing display. Your display's oil pressure actually looked kind of high, but then I saw that the engine wasn't warmed up yet.
My car is mostly stock - just a downpipe and catback, so I'm trying to keep the analog gauges working correctly.

 

Good catch, the engine wasn't warmed up yet in that video. Once the engine is warm the oil pressure is about 30psi when idling at 1000 RPM, and a very smooth & linear increase up to 100psi around 3500-4000 RPM. Oil Pressure might be a little lower with a stock ECU idling at 700-800 RPM, but I prefer idling at 1000 RPM to make the car a little easier to drive.

I'm interested to hear if a new pressure sender fixes things for your car. I removed and cleaned my stock sender with a small pipe cleaner while I had things apart to install the new sensor & oil filter pedestal, but that didn't change the readings.

 

I'm on my 3rd sender. The original got squirrely at about 13,000 miles, the second one lasted 20,000 miles, and the current one about 25,000 miles. Each time the symptoms were the same and a new sender fixed it. The shop manual shows how to check the sender's resistance with an ohmmeter. It should be "over 74 ohms" with the engine stopped, but I don't think it should be too much above that. My new sender is 79.1 ohms. I haven't installed it yet. The flaky one in the car is 97.4 ohms, and the previous flaky one reads 1,365 ohms. Per the shop manual, at idle (750 rpm?), 30 psi should give 43 ohms, and 45 psi should meter at 50 to 57 ohms. At 3,000 rpm fully warmed up, the oil pressure spec is 50 psi minimum. The OEM gauge's allowable indication error is twice the width of the needle, so there is some slop in the system.