oil pressure on 1hz - what causes is to drop and what can be done to 'fix' it?

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I do not know much about the hz but installed two after market oil pressure gauges + sender , one mechanical and one electric on my 2h. Worthwhile in my opinion, on the 2h gauges are not very accurate. The autometer and marshal gauges are much more real time responsive.
Did an aftermarket temp gauge too, I watch the numbers so I can turn the tunes up, carefree.

The 2h has 2 oil pressure relief valves with springs, the one on the block can be fiddled with, I trimmed my new spring one coil and packed with a thin washer. This can alter your oil pressure to adjustment of personal 'taste'..

Accelerating affects oil pressure, but braking shouldn't as much besides lowering revs creating lower pressure. It is directly related to your revs. If it does the same thing on accelerating and braking then it maybe an electrical gremlin, like a corroded earth.

After much research and observation I have concluded on the 2h that around 70-80psi(which is within factory spec) is optimal oil pressure for around 2000-2100 rpm. This is the minimum oil pressure required to spin centrifuge oil spinners (another aftermarket thing but use to come standard on the older 2h).

Type of oil and oil level makes a difference too. I believe you require mineral oil, synthetic oils would generally be too thin for your engine. Ambient temp does a little too.

Someone fluent in hz should chime in. Get a factory manual, a toyota one.

I am not overly comforted with the low oil pressure numbers that the 2h factory manual allow, I think around 7psi is ok at idle from memory. But I idle at lowest 30psi which is close to the lowest line on the factory needle. Better a bit high with lots of luscious clean oil lubricating everywhere in your engine. But not too high or you pop your oil filter, say over 100psi. Over filling the oil can cause this too, which can even bend or crack crank shafts.

But I wanted to keep my engine so worth the time and money.

The hz can get a million kms, which is something to be really proud of.

What oil do you have in there?
Thank you so much for that detailed reply. There's a lot to think about and respond to. I was watching it as I was driving a few minutes ago and it seems to be quite unpredictable as to whether it goes up to about quarter of the full range or at zero. Pretty much randomly. That would argue for a electrical fault or a sensor fault I think. But I am going to spend more time thinking about this. Again I greatly appreciate the feedback
 
I would like to thank all of you guys for your helpful responses. The consensus seems to be that 1HZ motors go a million Ks, wear slowly if you change oil every 5Ks, use genuine filters at least every second time, and use heavy diesel engine oil. The universal experience, including the views of old mechanics, is that 1HZ dash oil pressure gauges are very conservative so don't panic. Low on hot idle is normal. I expect my HZJ75 to outlive me, so you can't ask for more than that.

One last thing. This site is way better than any other and is visited by Legends in Their Own Time. Cheers, fellas.
 

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