Pete145 said:

Hi John,

I really don't think so, as the engine was essentially rebuilt and upgraded to a very authentic 595ss spec by Middle Barton Garage at the same time the gauges were put in.

Most of what you have listed have either been fitted as brand new parts or parts that have been inspected and refurbished during the rebuild. MBG also had it back and gave the engine a thorough inspection and re-tune after about 250 miles of post rebuild motoring. This is what makes it such a riddle.

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I know you don't think there is an issue with the engine...but there is. Sending units are really not effected by heat. They either work fine, stop working completely, leak, or read low all the time. If you see good oil pressure when the engine is cold, and low oil pressure when hot, then the sending unit is working fine and the engine has a problem. Take it back to Middle Barton, there is something wrong.
John

jjacob said:

I know you don't think there is an issue with the engine...but there is. Sending units are really not effected by heat. They either work fine, stop working completely, leak, or read low all the time. If you see good oil pressure when the engine is cold, and low oil pressure when hot, then the sending unit is working fine and the engine has a problem. Take it back to Middle Barton, there is something wrong.

John

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I'll try another sender unit first.

Have you tried wrapping the sender unit with heat insulation?
Or fit some sort of a heat shield/deflector?
If you have compressed air available, give the sender unit when hot a sustained blast of compressed air and see if the indicated oil pressure improves, or use a freezer spray (cautiously) or spray some water on it to cool it.

I'd have to agree with 'jjacob' above though.
At the very least I'd try a mechanical type oil pressure gauge on this rebuilt engine without delay, just to be sure there isn't a developing problem.

Had a friend once who had just rebuilt a VW diesel engine in a customer's car at his home workshop. Was using it for a couple of days to make sure everything was ok. Oil light came on, he assumed it was 'only a faulty sender'. Drove home, engine was wrecked. Big-time.

Al.

F123C said:

Have you tried wrapping the sender unit with heat insulation?
Or fit some sort of a heat shield/deflector?
If you have compressed air available, give the sender unit when hot a sustained blast of compressed air and see if the indicated oil pressure improves, or use a freezer spray (cautiously) or spray some water on it to cool it.

Al.

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Thanks for the ongoing tips everyone. I had a similar issue when I first got the car, pre-gauges and before the engine had been re-built a la 595S. The oil pressure warning light would come on periodically (while driving). The diagnosis I had was that the heat form the exhaust (without the shield) had indeed fried the sender, so the bottom of the pipes were wrapped, a I fitted a new sender and, voila, no oil pressure light.

I guess this experience has conditioned me to think that the same may be happening this time around, but the consequences of my thinking being wrong are serious, so I will investigate.

Is it generally normal for oil pressure to reduce when the oil gets to temperature? The oil will become less viscous, and will this decrease pressure?

I'll try the tips above (thank you) next time it's running hot, cool the sender down and see if the reading increases.

Sorry if i missed the answer- but where is the sensor mounted?

AndrewHarvey said:

Sorry if i missed the answer- but where is the sensor mounted?

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It's in the same place as the original sensor (see image), note the proximity to the exhaust, and the lack of heat shield. Hence my concern.

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When building my engine it was found that the oil pressure switch position - was a poor position for pressure indication.
Mine is mounted remotely and i recommend doing the same before panicking

AndrewHarvey said:

When building my engine it was found that the oil pressure switch position - was a poor position for pressure indication.
Mine is mounted remotely and i recommend doing the same before panicking

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Yes, I've heard of that solution before. So do you mount the sensor on the shelf to the right, and run a line to it?

There are kits on ebay or from car builder solutions
Mine is mounted in the oil cooler pipework and sits behind the coil.
You could do worse than buy a mechanical gauge, tubing and adaptor and see what you get.
It would show you the way forward for pennies......

Pete145 said:

Is it generally normal for oil pressure to reduce when the oil gets to temperature? The oil will become less viscous, and will this decrease pressure?

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Absolutely correct. As the oil heats up it becomes less viscous, so it will slip more easily through any larger than correct clearances. Also, as the engine heats up these clearances also get bigger.

Get a cheap oil pressure mechanical gauge and install in place of your current units. This will tell all.
John