Automobile Maintenance: Engine Vacuum Leaks

When a road-going naturally-aspirated gasoline engine is idling, there is vacuum in the intake manifold. Vacuum is any pressure that is less than the ambient atmospheric pressure. Atmospheric pressure is expressed in different units and it varies with altitude. Therefore we usually reference it at sea level. At room temperature (20-25°C), atmospheric pressure is 14.7 psi or 760 mm Hg or 29.9 Inches of Mercury or 760 torr etc. Vacuum at engine idle exists due to the fact that the throttle is fully closed and the little air that gets past the throttle is sucked in by the cylinders. When the throttle is gradually opened, the pressure inside the intake manifold increases and nears the ambient atmospheric value.

In the start of the above paragraph, I used the term road-going vehicle because in some race engines, there may not be enough vacuum even at idle. The race engines use long-duration camshafts and the amount of vacuum in an engine depends on the design details of the camshaft(s) like the valve overlap angle.

Nuclear Testing in the South Asia

The five declared nuclear powers, i.e., USA, Russia, UK, France and China are also the only permanent members of the United Nations Security Council. This elite nuclear club also has the the privilege of veto. These powers have signed the nuclear Non-Proliferation Treaty (NPT), forbidding any technical assistance related to nuclear weapons to the non-nuclear states. 

India was a vast country with a big economy, huge population and a powerful military but without the nuclear power status. Also India had border disputes with China and it could not really confront China without becoming a nuclear power. The move for getting nuclear power status and possibly a permanent seat at UNSC was undertaken in May 1998 by doing a series of nuclear weapon tests. In turn, Pakistan replied with its own tests. The earlier Indian test of 1974 was declared as “peaceful nuclear test” and hence new tests were needed for demonstrating nuclear weapons capability. 

Automobile Maintenance: Engine Cooling System (Update)

This is an update to the former article on the engine cooling system : http://syed-imran-shah.blogspot.fr/2015/08/automobile-maintenance-engine-cooling.html

Coolant Expansion Tank

To make things clear, a schematic diagram of the expansion tank is given here. The internal tube is shown as a dashed line. Real pictures of this tube are also added. This tube has a bubble flare on one side to facilitate the entry of coolant and a bevel on the other side to facilitate the exit of the coolant. A rubber seal is also mounted on the tube for sealing of coolant and vapours.

Automobile Maintenance: Testing of Electrical Relays

This write-up concerns the general-purpose electrical relays. The specialized ones like timer relays etc are not discussed here.


For testing of electrical relays, one must first understand their function and working principle. Fucntion of a relay is to allow the use of a low-amperes circuit to control a high-amperes circuit. By control is implied switching on and switching off operation. The low-Amps circuit is the control side and high-Amps circuit is the feed side of the relay.


Many online videos suggest that if a relay clicks, then it is working. Clicks are an audio test at best and does not confirm if a relay is actually working. A click confirms that the control side of the relay is good but nothing can be said definitely about the feed side based on a clicking sound.

Automobile Maintenance: Identification of Electrical Relays

Here I am discussing a topic which is very important for automotive safety and yet is rarely discussed. This write-up concerns the general-purpose automotive electrical relays. The specialized ones like timer relays etc are not discussed here.

Electrical relays allow the use of a low-amperes circuit to control a high-amperes circuit. They can have either five or four terminals but mostly four of them are used. Ignoring the fifth terminal, a relay has two ground and two power connections. The low-Amps circuit is the control side and high-Amps circuit is the feed side of the relay. Looking at the specific positioning of the terminals, one would think that plugging-in of the relays is fool-proof and that they can only be inserted one way but in reality it is not the case.