Engine oil pressure switch

Curious Dave · 12-20-2011, 06:26 PM

Does anyone know what the thread size is on the engine oil pressure switch that threads into the block? The auto parts stores have the thread size listed as M18 X 1.5, but from what I can see, the thread size looks more like 1/8" NPT. Any help on this matter would be greatly appreciated.

jimrm · 12-20-2011, 07:21 PM

I don't remember right now if it was 1/8" or 1/4", but I am sure it is national tapered pipe thread. When I installed my turbo I put in a "T" there for the turbo oil supply.

aisbell · 12-20-2011, 08:57 PM

It seems odd to me that an engine made in Japan where the metric system is used would include an oil pressure sending unit whose threads are 1/4" or 1/8" national tapered pipe thread. But the world can be odd, I guess.

jimrm · 12-20-2011, 09:42 PM

Here is what I found out on the Honda tech forum. Honda uses 1/8" BSPT. The British use a thread angle of 55° and NPT thread angle is 60° and the taper is 3/4" per foot. It looks like it could also be a ISO 7/1 thread which are also 55°

NPT threads may look similar to ISO 7/1 threads. However, ISO and NPT threads should not be mixed. ISO threads have 55o taper angle versus 60o for NPT. The NPT root and crest configurations are also different from ISO. For ISO threads pitch is usually measured in millimeters ( may be expressed in Inch). The pitch are different.

I know this doesn't clear it up entirely, but it's all the information I could find.

Curious Dave · 12-20-2011, 10:27 PM

Here's a description from the Autozone site: Duralast/Oil Pressure Switch (PS432) | 2003 Honda Insight Hybrid 3 Cylinders 1.0L Gas/Elec SOHC | AutoZone.com

Definitely not M18, but more like 1/8".

Curious Dave · 12-20-2011, 10:45 PM

Here's a better pic. http://i122.photobucket.com/albums/o...wpartimage.jpg That looks like 1/8" BSPT to me. Does anyone else agree? I'm also thinking that the plugged port directly below the oil pressure switch has a passage that connects directly to the oil pressure switch port. Funny, I should know this by heart since I rebuilt my engine several years ago, but I'll be darned if I can remember if the two ports connect.

The plugged port looks like it might have a M18 thread size.

http://i122.photobucket.com/albums/o...siteside-1.jpg Sorry for the pic being out of focus.