How should I start and run a cold engine?

land rover defender v8 engine rebuilt by leoxrovers.com

Starting a cold engine

When you start an engine there are a couple of things that you have to keep in mind in order to minimize wear and tear and also to prevent catastrophic failures such as cracked heads or blocks.

The lubricating qualities of oil

The first part of the equation is the amount of oil that is in the engine and able to lubricate the moving parts such as the camshafts and lifters. When the engine is off, the oil drains down to the pan. A little oil remains in the engine in order to lubricate the parts on the next start-up. The problem is that the oil is cold and thick and therefore the oil pump has a relatively hard time to get more oil to the moving parts. This results in wear and tear.

Should I first idle?

Now, some people advocate that you should first let the engine idle in order to get it ready for the road. This is thoroughly bad advice because it means that the engine will take longer to warm up to operating temperature. The oil will be cold and thick for a longer period with poorer penetration and lubrication qualities.

It is much, much better to start the engine and then drive with a light foot on the gas pedal until the engine has reached operating temperature. This is because the engine will warm up faster with a moderate load.

The critical role of the thermostat

The critical part of the engine warm-up phase is the thermostat. The thermostat is closed when you start the engine to prevent coolant from circulating from the heads and the block to the radiator. This means that the engine will warm up fairly quickly when you drive it. Once the engine has reached operating temperature, the thermostat opens and allows coolant to get cooled down by the radiator, thereby keeping the engine at the desired temperature.

The correct driving procedure until operating temperature

It is important to put load on the engine by driving but it is critical not to overload it by revving the engine too high. Letting the revs go above 3000 can be catastrophic for a cold engine, especially if the block and heads are made from aluminium.

This seems counter-intuitive. You might rightly argue that I just said that we want to minimize the time that the engine is running while below the operating temperature and surely the engine will warm up quicker if the revs are high? What nonsense am I spewing now?

Well, the other part of the equation is that the engine is not warming up at the same rate everywhere throughout the block and the heads. The engine will probably have hot spots where the aluminium has become hard and brittle over time while the surrounding areas have retained its flexibility.

What can go wrong if I rev the engine?

If you let the revs go up too high while the engine is cold, the hot spots will heat up much faster than the surrounding areas and the brittle aluminium can crack. If this happens to the heads, you are in a world of hurt and the repairs will be expensive.

If this happens in the block it is much, much worse. You will probably be searching for a replacement engine. But most likely you are going to sell the car for spare parts because to replace the engine is a nightmare.

Personally, I like to keep the revs below 2000 but that is because I had the heads crack on me. I was in a hurry one cold winters morning because I was late for work. Against my better knowledge, I revved the engine. When I stopped at the first traffic light my Landy had decided to throw a smoke-screen, engulfing myself and the surroundings in a bright white mist. A very expensive mist, as it turned out …

Removing the thermostat – a crime punishable by death

One last thought – a popular backyard mechanic fix for overheating engines is to remove the thermostat. The belief is that the thermostat restricts coolant flow (which is true) and somehow that is bad for the engine. As I have explained above, this is utter nonsense. The thermostat is critical and if any mechanic commits the cardinal sin of removing your vehicle’s thermostat – please take him to the backyard and have him promptly shot.

Overheating problems have specific causes such as a leaking head gasket or a failing viscous clutch. Removing the thermostat only masks the symptoms. It is infinitely better to diagnose the problem correctly and fix it.

While you are here, you are welcome to take a peek at our flagship Landy that is currently for sale.

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