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HJ60 oil pressure

G

Guest

Guest
Roman,
I cant remember where the needle sits when the engine is shut down, but that
has not changed. I have not yet tested to see what voltage gives FSD, am
now waiting for the new gauge to arrive from the dealer. Ordered it last
week, so should be here tomorrow or early next week.
 
G

Guest

Guest
On 6/2/05, Neil Paisnel <[Email address removed]> wrote:
hat
Neil,
If the 60 has an oil pressure gauge like the 80, voltage is not an
accurate indicator of the health of the system, but better than
nothing.
I have my instrument cluster stripped to pieces on the workbench and
am investigating how the gauge works. Well, the gauge is a very crude
instrument based on a bimetallic strip with a length of wire wrapped
around it, acting as a heater element. Deflection movement is
translated from linear to rotary with a very short fulcrum. The
tolerances are very loose and would give different readings form gauge
to gauge. The heater element is also subject to variations in battery
voltage and ambient temperature.
The gauge's heather element is connected to the battery and the
pressure sender acts as a variable resistor connected to ground. When
oil pressure is low, sender resistance is high. Current flowing
through the heather element is low enough and does not cause
deflection of the bimetalic strip - the pointer is at the bottom of
the scale. Higher pressure lowers sender resistance, hence more
current flows through the gauge. That deflects the bimetalic strip
more and moves the pointer up the scale.
I noticed that recently the pointer in my gauge dropped lower than 0
when ignition key was off. When the engine was running it showed
pressure lower than normal. Readjusting the bimetalic strip rectified
the problem. The same may have happened in your case, too. The FSM
does not provide any current values allowing for gauge calibration, so
measuring actual pressure with a calibrated gauge is the only way to
make sure the oil pump is working properly.
And the reason why current rather than voltage is used to measure oil
pressure is possibly to even out pulsations in the system but still it
is a very rudimentary method of indicating pressure.
--
Rgds,
Roman (London, UK)
'92 HDJ80
 
G

Guest

Guest
I have measured oil pressure with another trusted gauge, and it is showing a
good pressure, whether it is within spec or not is debatable as I have yet
to see figures for this engine. All diesel spec books at the local diesel
engine repair workshop have specs for all other Toyota engines, and other
figures for this engine (2H) but there are no figures for oil pressure. So
yes it could well be in spec, but there is no way of knowing for sure. If I
saw book figures for this engine then I would know.
As for the sender, I am not so sure that it does react to the pump pulses as
you say. I applied a constant pressure to the gauge via an airline and
regulator slowly increasing the pressure up to 8 bar. 24v fed though a bulb
and the sender. The bulb pulses the same as it does when connected to the
running engine. Pulse speed from 20 per min up to about 45 per min at 8 bar
Anyway, for now all I can do is wait till the new gauge arrives
 
G

Guest

Guest
Well, I finally got the factory oil pressure gauge reading correctly. It
was the display unit. The bi-metallic strip had become too hot and bent out
of shape, causing the needle to read incorrectly. I believe this was caused
by a failure/ sticking contact in the sender unit.
Neil Paisnel
 
G

Guest

Guest
On 7/26/05, Neil Paisnel <[Email address removed]> wrote:
out
sed
Hello Neil,
I almost forgot but I promised to measure the oil pressure sender
output with a scope. Well, I did it but as I was not sure what to make
out of the readings, I kept it at the back of my mind for a while.
OK, the scope registered a series of iregular 12V impuses, some were
square, some just spikes. There was some very vague pattern of impulse
frequency increasing in relation to engine revs, from which I can
deduct the following:
- oil pump revolutions produce pressure peaks which are translated in
the sender's tranducer into short current impulses. These impulses
drive a coil in the sender and cause the bimetalic strip to bend and
close the contacts. The ON/OFF impulses generated by the contacts are
send to the gauge which translates the frequncy of the impulses into
current that heats up another bimetalic strip. It deflects the
pointer.
The whole idea seems to be to introduce a very long hysteresis so that
the pointer does not vibrate at the oil pump frequency.
As a result of this the gauge is so inaccurate that it only shows if
the pressure goes up or down, but it's readings have little
relationshiop to the nominal pressure. I have an idea how to design a
device that would accurately measure oil pressure in relation to
engine revs but it haven't got a datalogger to register sender output
under different driving conditions.
How much did you pay for a new gauge?

--
Rgds,
Roman (London, UK)
'92 HDJ80
 
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