Gauge sensor and sender threads

[gt_james]

I've bought some gauges recently for my race car and thought I'd summarise some info here, in case anyone else wants to fit aftermarket sensors.

On a stock S3 at least, you're given:

• Oil pressure gauge in the cluster, sender LH side of the rear plate, big round thing. The stock sender thread is 1/8BSPT.

• I don't think there is a low oil pressure warning light.

• Water temp gauge - pretty slow responding and no actual temperature readings, just C and H. Sender is the small one in the rear plate next to the above oil pressure sender, and just above the heater outlet pipe. The stock sender thread is 1/8BSPT.

• A low water level warning light. Switch is in the top of the radiator. Sorry don't have the thread for this.

• A low oil level warning light. Switch is in the sump, LH side. Sorry don't have the thread for this.

• The choke has a water temperature sender in the back of the thermostat housing. It's an M16x1.5 thread.

In my race car I won't be running a stock cluster, as the car came without one, won't fit with the dash bar of the roll cage, and for a track car I think the stock water temperature gauge doesn't really cut it anyway. Also lacking low oil pressure warning (idiot) light.

I plan to run oil pressure, oil temperature and water temperature gauges, as well as warning lights for low oil level, low oil pressure and low water level.

Some gauges like defi use the same 1/8 BSP thread as stock. Most gauges seem to use 1/8 NPT, which is what the gauges I bought use.

• I will leave the stock water temp and oil pressure senders in the rear plate but won't be using them.

• For water temp gauge I will use an M16 to 1/8NPT adapter in the thermostat housing (no electric choke on my engine set up). In my opinion the rear plate is a better place for the sender, but I didn't want to tap my rear plate incase I ever want to use a stock sender, and I'd be worried about swarf getting in the galleries. As the 1/8 bspt and npt sensors are the same diameter, an adapter would space the sender away from the block, I've read that can cause accuracy issues. The water m16 thread in the thermostat housing should allow an adapter that won't space the sensor out much and should work fine. A sensor in the upper radiator hose is less than ideal.

• For my oil pressure gauge, oil temperature gauge and low oil pressure warning light I will run a cheap sandwich plate under the oil filter with 3x 1/8 NPT ports. Again easier than adaptors and drilling out the ports. I'll add a 5psi low oil pressure warning switch.

• I will use the stock low oil level and low water level switches for warning lights also.

[gt_james]

I've bought some gauges recently for my race car and thought I'd summarise some info here, in case anyone else wants to fit aftermarket sensors.

On a stock S3 at least, you're given:

• Oil pressure gauge in the cluster, sender LH side of the rear plate, big round thing. The stock sender thread is 1/8BSPT.

• I don't think there is a low oil pressure warning light.

• Water temp gauge - pretty slow responding and no actual temperature readings, just C and H. Sender is the small one in the rear plate next to the above oil pressure sender, and just above the heater outlet pipe. The stock sender thread is 1/8BSPT.

• A low water level warning light. Switch is in the top of the radiator. The stock sender thread is M11x1.25, and a lot of aluminium radiators unhelpfully use a 1/4"NPT thread.

• A low oil level warning light. Switch is in the sump, LH side. Sorry don't have the thread for this.

• The choke has a water temperature sender in the back of the thermostat housing. It's an M16x1.5 thread.

In my race car I won't be running a stock cluster, as the car came without one, won't fit with the dash bar of the roll cage, and for a track car I think the stock water temperature gauge doesn't really cut it anyway. Also lacking low oil pressure warning (idiot) light.

I plan to run oil pressure, oil temperature and water temperature gauges, as well as warning lights for low oil level, low oil pressure and low water level.

Some gauges like defi use the same 1/8 BSP thread as stock. Most gauges seem to use 1/8 NPT, which is what the gauges I bought use.

• I will leave the stock water temp and oil pressure senders in the rear plate but won't be using them.

• For water temp gauge I will use an M16 to 1/8NPT adapter in the thermostat housing (no electric choke on my engine set up). In my opinion the rear plate is a better place for the sender, but I didn't want to tap my rear plate incase I ever want to use a stock sender, and I'd be worried about swarf getting in the galleries. As the 1/8 bspt and npt sensors are the same diameter, an adapter would space the sender away from the block, I've read that can cause accuracy issues. The water m16 thread in the thermostat housing should allow an adapter that won't space the sensor out much and should work fine. A sensor in the upper radiator hose is less than ideal.

• For my oil pressure gauge, oil temperature gauge and low oil pressure warning light I will run a cheap sandwich plate under the oil filter with 3x 1/8 NPT ports. Again easier than adaptors and drilling out the ports. I'll add a 5psi low oil pressure warning switch.

• I will use the stock low oil level and low water level switches for warning lights also.