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

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I'm aware that a very old 1hz like the one in my 80 has a lot of wear and potentially blow-by.

I'm noticing when driving that the oil pressure is not coming much above 1/3 anymore and when idling (hot motor) the pressure goes to about 1/6 on the gauge.

I always change the filter with a genuine one and do oil changes roughly every 10000 km. I use Delo 400 multigrade oil. I always use an oil system flush (Nulon is the one I use) as part of the oil change routine.

I've not replaced the oil pressure sender or any other parts of the oil system besides replacing the filter when I do oil changes.

I've tried stuff like 'worn engine treatment' etc. in the oil and really those products do nothing that I can determine apart from perhaps a very short term improvement in oil flow by improving the wear properties.

Putting aside the fact that the motor is very old and worn, is servicing the oil pump, etc. a feasible thing to consider and is it something that's relatively easy to do with the motor in the vehicle?
 

mudgudgeon

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Most likely problem is just general wear on bearing surfaces leading to out of spec clearances on things like crank main and big end bearings and crank journals surfaces, and camshaft bearings and cam journal surfaces.

As bearings wear, clearances increase, your oil pump is pumping the same amount of oil into a bigger gap. This equals a reduction in pressure. Oil also escapes out of these areas faster, so again a reduction in pressure.
The pump itself will also wear, clearances on the impeller and thrust surfaces will increase, reducing effectiveness of the pump.

Solutions?
- Replace worn bearings. If crank journals are worn, this will limit how effective this is.
- Rebuild the oil pump. Same as above
 
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Not too familiar with hz and it's longevity, (think they can get a million k's) but on the 2h, it can be increased with the pressure relief valve by packing the spring with washers. Not that this is advisable.

The 2h can blow oil filters with too much oil pressure if the relief valve gets stuck. I mucked around a fair bit with oil pressure with electric, mechanical gauges and the relief valve, relief spring length and tension, and different oil viscosity. Thicker oil does a little bit, but not much. Old oil gets tired too. Warm weather and long drives makes the oil a bit thinner too, not by much.

If any comfort, a digital oil pressure gauge can let you know exactly what psi you have if you measure it against a mechanical gauge. I find that the ome gauge is not very accurate. The ome gauge can read 1/3 but be 70 psi on the digital, which is plenty. Over 100psi you may pop the filter.

As long as psi is in fsm spec, you got be happy with that. For the 2h , fsm says as low as something like 7psi at idle is ok, but I would be worried to be that low.
How many k's you got? If it is just worn, that is life.
 
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Thx it definitely is happening only with the engine warmed up. When the motor first starts the oil pressure shows a good measure on the gauge and as it warms up the pressure readings go right down. I checked the oil level today since I'm in the engine bay doing the fender panel job and it's good, but I'll check again when running just to be sure.
 
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Thx it definitely is happening only with the engine warmed up. When the motor first starts the oil pressure shows a good measure on the gauge and as it warms up the pressure readings go right down. I checked the oil level today since I'm in the engine bay doing the fender panel job and it's good, but I'll check again when running just to be sure.

It shows good pressure initially because the oil is thick from lack of heat. Once the temp of the oil starts to rise, the viscosity will go down. Therefore, the pressure goes down. That, as stated above, can be due to several things. I would say that it is most commonly associated with a worn oil pump.
 

mudgudgeon

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Good call on checking with a gauge and not just relying on the OEM dash gauge.

Without a secondary gauge and relying on the factory gauge, there's no way to know how much of a drop is actually occurring
 
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Soooo. what is the best way to set up to have a secondary, proper oil pressure gauge even if it's not a permanent thing fitted in the dash but one that can be connected when required for testing? Is there a need to monitor both oil pressure and temp or can it be presumed that oil temp and coolant temp are basically matched?
 
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search on here, or google, i did it along with a 'bypass oil filter rave'. I feel naked now without my extra oil and temp gauge.
mind you, always a little something on old cars..
 
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oh
search on here, or google, i did it along with a 'bypass oil filter rave'. I feel naked now without my extra oil and temp gauge.
mind you, always a little something on old cars..
oh, 690k's! well no wonder, there is a guy here who got a million k's on his 12ht with the same oil pump. Whilst you probably alright for a bit, personally I would be slowly be gathering parts for a rebuild for the future. Parts go up in price, not as quick as vegies, but noticable.
I am slowly building a second 2h.
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1668689709915.png

The extra gauges just give you some reassurance.
 
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I have a Watchdog TM2 for coolant temp (sensor mounted to top of motor near radiator hose connection), but need to figure out what do to if I want a permanent oil pressure monitor or not.
 
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This may trigger a new debate but, I change oil every 5000Ks, as recommended by the manufacturer. Everybody tells me the recommendation for today is 10,000 but, call me cynical, I believe the rationale is, wear out your motor faster and be forced to buy a new one.
 
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This may trigger a new debate but, I change oil every 5000Ks, as recommended by the manufacturer. Everybody tells me the recommendation for today is 10,000 but, call me cynical, I believe the rationale is, wear out your motor faster and be forced to buy a new one.
with ya there brother! clean oil is the best
 
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What are the actual oil pressure specs for a 1hz motor? I'm aware the Toyota factory gauge in diesel vehicle with an oil pressure gauge is uncalibrated.
 
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What are the actual oil pressure specs for a 1hz motor?
I'm not familiar with the 1hz but a rule of thump is: rpm / 1000 in bar oil pressure

Idle at 600min-1 -> 0.6bar oil pressure (maybe 7.5PSI)
1500min-1 -> 1.5bar or 22PSI
3000min-1 -> 3 bar or 45PSI

often the limits by the manufacturer are a little bit lower, so the upper values are on the "good" side. In real life, a healthy engine has more then this.
The background is, that there is a minimum pressure needed to push the oil into and through the crankshaft against the centrifugal force, to get to the lubrication points of the connecting rods.

I've not replaced the oil pressure sender or any other parts of the oil system
Usually the oil pump is not the problem. Worn bearings can be.
If there is a drop in oilpressure under higher rpm, then maybe the inlet filter/screen of the oil pump is clogged. If there is a drop in oil pressure at same rpm but different load, it can be a sign for worn bearings.

I had a broken oil pressure sender at my J4, replaced it and everything was fine, but over a time of around 4-5 months the oil pressure trent dropped. I did a oil change but no change in behaviour. I removed the sender and tested with a air pump of my bicycle (with gage) and: The sender gave only half the pressure, BUT constantly over the whole range. Very tricky, because the behaviour of the oil pressure seemed reasonable, but too low.
A new sender fixed the fault.

BUT, as long as you not have verified the sender to be faulty, consider you have a real oil pressure "problem".
 
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I've had 3 1HD-T's and talked with a few others that had this motor - no-one sees much pressure in these engines. It's usually just above the low pressure mark when at operating temp. Mileage on all was around 170-220k km.

If ppl have other experience I'd like to know.
 

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