Tuesday, April 1, 2014
What does 2 minutes cost?
On this, the first day of April, I wanna wish my wombmate, my sister Elizabeth, a very Happy Birthday. You are loved more than you know Liz- heres hoping its a great day for ya!!
What can 2 minutes get ya? Warm-ups part 1
Well, to speak for the machines, let me clue ya in. We all have been told for years that every cold start on an engine is detrimental and does irreversible damage. Realistically, we can't much avoid that type of initial damage without pricey pre-oilers, but driving and loading a cold engine is far more damaging long term and quickly takes over as root cause of premature engine failure.
Some of the damage is alleviated by using good oil, but loading a cold engine and cold oil cannot help but remove miles from the tail end of the engines life at a more rapid rate regardless. Define 'cold' you say. OK, so, some parts of the engine run very hot, some run cooler. When possible, everything under the hood should roughly half of its normal operating temperature before putting any load on the engine- 'rule of thumb' there if ya need one.
In the tropics or temperate summer, a minute or 2 warm-up is enough to eliminate most issues. In the colder climates or temperate winters, letting a large engine idle for as much as 15 minutes may be needed to get oil circulating normally and combustion happening efficiently. Small aluminum engines need less warm-up, big iron engines need more. Ask truckers about idling vs. restarting those big turbo diesels they run for a million miles or more. These folks leave their rigs idling all night long to prevent cool-down and thus any need for warm-up.
Have you ever cracked or broken something in the winter cold, usually plastic, that you know during the summer months would have taken that minor abuse without incident? Well plastics and engine metal have many similar characteristics- wax point, crystalline structure, flexibility and brittleness numbers. These similarities in physical properties lead to similarities in behavior. In cold weather pliability of materials like these is replaced by brittleness. The term 'glass-point' is used to describe the property of brittle breakage from extreme cold.
As an engine warms, the metal gains pliancy. Cold metal under high stress will crack in microscopic spiderwebs that slowly (or sometimes rapidly) weaken the metal or warp parts and tear them apart over time. Crystalline structures can change, twist, and warp from rapid heating/ cooling, not to mention the stresses of torque production required to push a vehicle down the road.
One significant issue that I have repeatedly dealt with and is caused directly by cold start/ drive-aways is blown and sheared, and thus leaking, gaskets. An engine started cold and driven immediately or shortly thereafter, shows very uneven rapid heating, poor lubrication, oil contamination with acids and water, abrasive soot production, and transient thermal stresses. When the cylinder heads on an engine heat up fast and the block is still cold, the head expands and literally slide across the block face, tearing the head gasket or the intake gaskets on V design engine.
When the coolant has had time to circulate through the engine and heater core to bring the entire system up to a hundred or so degrees before stressing it, the metal of the engine will stay straight, strong and true for much longer, and thus gaskets stay happy and fluids stay where they should. Allowing the temperature to equalize across the block and head also allows time for the oil to warm a bit.
Another consideration is the simple fact that parts just don't fit like the engineers designed them to until they are up to operating temperatures. Normal temperature for an engine is when the coolant is around the boiling point of water (100 C, 212 F at 1 atm)- meaning most parts are running hotter than that- some hundreds of degrees hotter. This heating to very high temps rapidly while other parts are still cold is a cause of much wear and damage.
This is how exhaust valves start to leak oil and make blue exhaust smoke: the valve heats up to 1000 degrees (in a gas engine) and expands while the valve guide (bronze usually) are still cold and small. Thus, the valve fits extra tight and galls and tears at the bronze until it warms up and fits right- unfortunately, the damage is done, metal has been permanently removed and the valve will never fit tight in its guide again. The faster that heating happens, the more extreme the damage and more rapid the degradation of performance and longevity.
So it comes down to this: slow heating helps save parts and leave metal where it is supposed to be, allowing engines perform better for longer.
Thats it for part 1, Check back Friday for the rest of this article. MW out. :-)