Oil pressure sender what thread?

Fitting oil pressure gauge etc to my mk1 and am confused about the thread on the sender. Have seen lots on fleabay that are 1/8th npt what ever that is but i am sure i remember reading somewhere the golf was 10mm? Anyone know? Also toying with which port to mount sender, low or high pressure. Anyone know the values for the current warning light trigger pressures? Thinking the low pressure on the head might be better as it'll tell me when i have low oil pressure at the head not that i have no oil pump? cheers

muppetlab said

 Also toying with which port to mount sender, low or high pressure. Anyone know the values for the current warning light trigger pressures? Thinking the low pressure on the head might be better as it'll tell me when i have low oil pressure at the head not that i have no oil pump?

The low switch is 0.3bar which is around 5psi. The high pressure switch is 1.8bar which is about 26psi. And the placement you are thinking about, on the low side, is correct for your thinking about the warning (low would warn about the entire system).

NPT is National Pipe Thread, or something like that and is a common pipe thread. The Volkswagen ports for the oil switches are 10mm. I can't remember the exact thread pitch but it is something like 1 or 1.5 per millimeter.

m10x1
i may be wrong but i think 1/8 nbt is the same as m10x1? Not 100% on that

No. Don't even try mixing the two. NPT is a tappered thread and 10mmX1 is a straight thread. The diameters might be close the the thread pitch and taper will destroy one or the other depending on which is softer.

Okay thanks so i need to find a 10mm sender, not an npt one. cheers folks most helpful. If only setting up my damn webers was this easy!!

Doesn't matter which port you mount the pressure sender to, they both see the same pressure, it's the switch that reacts differently.

yeha said

Doesn't matter which port you mount the pressure sender to, they both see the same pressure, it's the switch that reacts differently.

That is not true. The port on the filter mount will only show the pressure that the oil pump puts out. The one on the side of the cylinder head will cover the entire oiling system except for the followers. So if the sender is at the head it will show low pressure if say a main bearing is toast, or if a passage is blocked or the system springs a leak say at the head gasket. The port at the filter mount will only indicate that you have an oil system problem when you run out of oil, too late then.

this is true, on my 2.0 8v the pressure was much lower at the head than at the filter housing.
It had worn cam bearings and the pressure dropped low enough when warm to trigger the pressure warning light, but at the filter housing it was 'healthy'

Apologies, I was thinking of the small block with the 2 senders in the head.

yeha said

Apologies, I was thinking of the small block with the 2 senders in the head.

No problem by me. Correct in that they are both on the same passage with those motors. Guess due to the lack of a filter mount that was the most simple way to make the warning system work.