Oil pressure gauge shows zero! Only on really cold mornings.

[ryan2022]

Hi guys, I have a Mazda B4000 (2001)

The truck has roughly 80K miles on it, and runs great. I have no issues with oil pressure once its warmed up, or even when its cold, OR when its cold after a run earlier in the day.

When I'm starting it for the first time of the day, and its bloody cold out, the gauge shows zero, as in doesnt move, until 1-2 minutes, then it flicks to the normal operating point instantly. Almost like the needle was stuck.

To me this is a sticky gauge, or an issue with the sensor or sending unit. I figure if its a oil pump issue, itd show itself at other times. Any thoughts? Its got me a little bit spooked. The engine sounds smooth, and runs perfectly even for the short period the guage shows zero.

Any way I can check this, without hooking a guage up to it?

Ryan

 

[Dune Runner]

I'd start by replacing the sensor. What weight oil are you running and when did you change it last?

 

[RonD]

I believe the Mazda's like the Ford's have oil pressure "switches" so they are either on or off based on a preset pressure, I think its about 6-8psi

So your "sending unit" is probably going bad.

If oil pressure was actually 0 you would hear loud lifter "ticking".

Real oil pressure sending unit and gauge setups have varying oil pressure, from idle to high RPM, and oil pressure would read higher at cold start and then go down as oil warmed up.
This doesn't happen with Ford, or Mazda, truck gauges, so they are "idiot" gauges
Like an idiot light with a needle instead of a bulb.

 

[kimcrwbr1]

Just change the sending unit if you have a guage it is not a switch, make sure the guy at the parts counter knows that. It may be that just after sitting for a long time it takes a bit to build pressure up because the oil drains down slowly from a bad check valve. The only fix for that is a new oil pump. Just start it normally and dont give it gas until the pressure registers.

 

[kimcrwbr1]

Just change the sending unit if you have a guage it is not a switch, make sure the guy at the parts counter knows that. It may be that just after sitting for a long time it takes a bit to build pressure up because the oil drains down slowly from a bad check valve. The only fix for that is a new oil pump. Just start it normally and dont give it gas until the pressure registers. You can add a mechanical oil pressure guage that will tell you for sure if it is the oil pump check valve. It can over a period of time cause damage to the rings and bearings in the engine, something to consider. Starting an engine cold is a terrible thing to do. You can try flushing the oil system drain 1/2 a quart of oil out and add ATF and run it around 100 miles. Then drain it good and put in a motorcraft oil filter maybe put in some lucas oil stabilizer to protect the internals for cold starts.

 

[ryan2022]

Thanks guys, I figure its a sending unit. It just struck me as strange taht the engine actually started really well, rean nice and smooth with little to no noise. I'm betting on a bad sending unit. I may plug in the block heater tonight, to see if it changes anything.

I'll source out the sending unit. I love working in the snow.

 

[ryan2022]

To add to that. I just changed the oil with 5w30 synthetic with a new Motomaster filter....I think its a fram, looks identical.

 

[kimcrwbr1]

If you still have the dry start condition drain and add a quart of the lucas sync oil stabilizer it will protect your motor better for cold starts the worst thing you can do to a motor is start it especially if it dont keep the oil primed up to the crankshaft where the guage takes its reading.