Electrical or Mechanical Oil Pressure Gauge?

Monitoring Engine Oil Pressure

Keeping check on an engine’s oil pressure is one of the key readings on race cars and road cars alike. Here at Merlin we stock gauges for this very purpose. From the retro looking Smiths Classic gauges to the hi-tech Stack Pro Control, we have a gauge to suit every application.

There are many options to choose from, but the main criteria is to select whether to use an electrical gauge, which uses a sender to send an electrical reading to the gauge. Or a mechanical type gauge, which uses a capillary tube to supply oil to the back of the gauge. There are pro’s and con’s for both types of gauges. Mechanical gauges tend to be extremely reliable and accurate, often used in race car applications. But at the same time, it is not always suitable to have oil entering the cockpit. The electrical gauges obviously eliminate this, but in some instances, it is not always easy to fit the relatively large pressure sender in to the engine.

Below are some top tips on fitting both types of oil pressure gauges.

Electrical Gauges

Electrical gauges use a sender to send a signal to the gauge. It is important that the correct sender is used with the gauge. For example, a VDO pressure sender will not work with a Smiths gauge. This is not always the case, but it is a general rule of thumb.
The sender must be fitted somewhere in the oil system. This is often screwed in to the engine block where an existing low pressure switch is fitted. The switch is removed and the sender is screwed in. Or, if the switch is to be kept, a T-piece is screwed in, the switch screwed back in to the T-piece and the sender is screwed in to the side of the T-piece. Various T-pieces and adaptors are available, meaning that most threads can be catered for.

The analogue type electrical senders are fairly large in comparison to the tight spaces in an engine bay. For example, a VDO analogue pressure sensor measures 50mm tall and 45mm across it’s diameter.

With this in mind, it is possible to remotely mount the sender using Goodridge 600 series hose and fittings. The Goodridge hose is screwed to the T-piece or adaptor, and is then run to anywhere that is suitably sized to take the sender. This is often on an inner wing or bulkhead. The sender can then be held in place using a bracket or similar.

Not only does this make fitting easier, it also prolongs the life of the sensor. All analogue sensors have small moving parts inside which can be susceptible to damage due to vibrations from the engine when screwed straight in to the block.

This method of remote mounting pressure sensors is not needed if using a Stack Pro Control or Professional oil pressure gauges. These ranges use solid state sensors which have no internal moving parts, and the sensors are physically smaller than the analogue versions.

Mechanical Gauges

Many race car applications use mechanical pressure gauges as they can often be more accurate, giving an instant response to any drop in pressure. As mentioned before, the main thing to bear in mind is that oil is fed to the back of the gauge, within the cockpit. The pipe (or capillary tube) for these gauges are sold separately (with the exception of Stack gauges). There are two main variants for this.
Firstly is using the black nylon pressure pipes. These come ready made in two lengths, either 1.5 metres or 3 metres long. They come with the appropriate female threaded union on one end for the back of the gauge. The other end has a 1/8BSP female union. This end can then be attached to the engine block using either a male to male threaded adaptor, or via a T-piece as described above. We have many threaded adaptors to suit most applications.

The second method is to use Goodridge 600 Series hose. Connected in the same way as the nylon pressure pipes, using two specific Goodridge unions. The length of this can be determined by you. This method is often used by race teams wanting a reliable ‘fit and forget’ oil pressure pipe.