May 2008

Date Event
05/05/2008

Oil Pressure.

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 2 %.  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  BSP (19 TPI.)  We found a suitable 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 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  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  BSP (Male) to 1/8 NPT (Female)

 

   

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