Date: Tue, 15 Dec 1998 12:56:01 +0200 From: "Roy Björkstrand" <nospamroilonopsamut.fi> Subject: Re: Best method for morning warmup
Justin VanAbrahams wrote: > Ilia Papas wrote: > > Is it bad for the engine to just > > turn it on and leave it for 5 or 10 minutes? Also, while driving the > > car with a cold engine, is it ok to drive it at high rpm's to warm it up > > faster or should I just drive it under 3000? Yes, but it is important to keep the sylinder pressure as low as possible too (don´t push the pedal too much even when driving at low rpm.). Also raise your rpm slow (less acceleration on the parts of the engine). > The second reason is oil pressure. The engine is designed to > operate at a certain level of oil pressure. This pressure is > directly related to heat - less heat means less pressure. By > letting the car sit for a while at idle and warm up, you end up > running the car much longer on low oil pressure than if you > just started out driving right away, heating up the engine > and getting to normal oil pressure faster. > -Justin The oilpump gives only volume and the pressure is relative to the "blocking" or "strangling" of the oilsystem. We should actually speak about resistive pressure (I made this term up, don´t know what word I should use). ie. if you have a garden hose you can adjust the pressure of water by putting your finger on the end of the hose. Resistive pressure of the oilsystems depends on how thick the oil is (cold oil = thicker oil = more pressure) and how freely oil can flow (tolerances at bearings, oil channels...). As a conclusion: less heat more pressure, though the pressure comes up with the rpm. (greater volume - higher resistance at bearing and channels). I have always wondered what happens inside the engine if it is heated up fast. How high are the thermal stresses (block is cold from the outside and hot from the inside) compared to the slow heating? Does the pistons, if it is for example aluminium, expand faster than the block? Due to these questions I´m a "slowheater". (One could also ask what is the REAL difference between "slow" and "fast" heating). I live in Finland and we have pretty cold weather sometimes. I use, when ever it is possible, a block heater. Doesn´t cost much - and it saves 0.1 litre of gasoline at every coldstart. (BTW did you know that one cold start wears the engine as much as does 500kms with a warm engine.) I let the engine run for a minute or two and then I take of driving with 1st gear and 1500rpm to the main road (100 meters). I don´t give "full power" untill the engine is warmed up. -37C and survived 99 -82 900i -85 900i -91 Roy
 |
 |
 |
 |
 |
