Last month on my way back from the
local JDC meeting my attention was brought to the the oil pressure
reading. I had arrived back home, so the engine was warm, at idle
speed, the oil pressure gauge looked as though it was barely reading. It was
dark so it was difficult to see exactly what the reading was but my guess
was around 10 psi. the oil pressure light was out and there were no
untoward noises coming from the engine. The pressure on the open road going
to the meeting was about 25 psi. Nothing remarkable but no cause for
concern either.
The
following day I called Nostalgia to discuss my observations. Overnight I had
concluded the problem was probably with the oil pressure sensor. I needed to
find out if Nostalgia had changed the sensor when they did the engine swap.
They had, the sensor that was fitted was my original sensor, because the
sensor that came with the engine was even more inaccurate. The
accuracy off the oil pressure gauge is directly proportional to the accuracy
of the sensor and they must be a matched pair. Manufacturers of gauges'
manufacture sensors calibrated to an accuracy of around 2½
%. Equally car manufacturers often specify the accuracy of the
gauge and sensor they want for their vehicle. All this is a long
winded way of saying I had changed the oil pressure gauge for a new one from
the Smiths Classic Range and connected it to the original XJ6 sensor. It
worked, but I suspect it was under reading because it was not calibrated to
work with the new gauge but the XJ6 original gauge. Secondly it was
more than 25 years old and probably tired.
I called "Speedy Cables" and
ordered a new sensor to match the gauge and an adapter to match the XJ6. the
adapter was needed to match the thread of the new sensor to the thread in
the XJ6 Block. the usual prompt and efficient service delivered the parts
next day. A couple of days later when I came to fit them discovered
the adapter did not fit the engine block. I spoke to Andy Barraclough
at "Speedy Cables" who said the XJ6 block is tapped to 3/8 BSP and he would
send me one. Last Friday the replacement adapters were delivered only to
find that they were the same as I already had. This time I did
what I should have done in the first place when I discovered the adapter was
wrong. I went to see my friend John Hopkins. Between us we measured
the thread of the old XJ6 sensor and determined that it was ¼ BSP (19
TPI.) We found a suitable ¼ BSP union and screwed it in to the XJ6
Block a perfect fit. so we knew we had correctly identified the
thread. The adapter we required is ¼ BSP (Male) to 1/8 NPT (Female) to
match the Sensors to the XJ6 Block. A quick look through the "Speedy
Cables" Web site shows there is not a suitable adapter listed. I've
e-mailed then to see if they can help.
Meanwhile John had his
thinking cap on. Today he came up with a solution. He turned down on
of the 3/8 BSP adapters an cut a new ¼ BSP thread . The problem
was the wall thickness of metal that screws in to the XJ6 block was pretty
thin and may shear off when being tightened. Johns solution was to male a
collar that fits inside the adapter narrowing the bore but restoring the
wall thickness of the adapter. the collar was held in place with "Loctite".
This afternoon, armed with a
modified adapter, I fitted the new sensor to the XJ6 Block, topped up
the oil and started the engine. Indicated oil pressure is much better around
35 PSI, @ 1200rpm, cold, at least a 10 psi increase. According
to Haynes Manual for the engine the oil pressure should be 40 PSI, @
3000rpm, hot. I confidently expect to achieve this when I take the car out
to road test it.
Oil Pressure Gauge 0-100 psi
(Smiths Classic Range) Pt No: BP-2404-00
Oil Pressure Sensor (700kN/m2) Pt No: PTR1810-1-P
Adapter ¼ BSP (Male) to 1/8 NPT (Female)
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