Contour Enthusiasts Group Archives Forums General General Should I let the car warm up?

Originally posted by BlackE1:

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My friends father did this except for the hopping in the car part, he went out side and his BMW was gone.

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Originally posted by sigma:

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Originally posted by striker2:

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Originally posted by Rishodi:

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Originally posted by striker2:

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the best thing you can do is start it and drive. you actually wear off mor of the cylinder wall when the engine is cold than when its warm. the fastest way to warm it up is to drive it. however it takes the average car about 45 minutes to warm up.

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45 minutes? I don't think so!! It takes maybe 2 minutes for hot air to flow through my vents in the winter after starting my car up, and it can't take too long for the engine to reach its ideal temperature after that.

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the optimal operationg temp for an engine is about 210 degrees and it takes roughly 45 min to get there. the aluminium engines may warm up faster but our blocks are cast iron. when the engine is cold you actually wear about .008 off the cylinder wall for every hour idleing at that temp. you wear less than .002 off the walls when its at optimal operating temp.

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1> I don't see how those numbers could be correct. Using that math within a year of normal driving given what the average car sits at idle between traffic, start-up, and traffic lights, even at optimal temperature, an engine will have several mm of cylinder wear in just a year. There'd be no cylinders left after a couple years.

2> Assuming you're correct and that an engine at optimal temperature is 1/4th as harmful to the engine as one that's cold, why again would I want to just take off and drive?

For one, that relationship between 0.008 and 0.002 on the temperature curve would be non-linear, it would be a logarithmic curve of some sort. So, while it may take 45 minutes to fully warm an engine, that 0.008 done at "cold" is done right at startup and just a few moments thereafter. Cylinder wear would quickly decrease within a few moments to, let's say 0.004, then slowly decrease over the next 40+ minutes until reaching 0.002 in 45 minutes. Almost all of the period of high wear is done right at start-up.

So, in your rush to warm the motor 'because that does less wear', you drive it. Now, instead of having a cold motor sit at 750rpm doing 0.008 of damage, you're driving it and doing five times that because the cylinders are pumping 5 times faster in that initial time of high wear.

In those first few moments of high wear, you multipled the wear several times what it would have been sitting at idle. Those first few moments of high wear by revving a motor at its' 'weakest' will vastly offset the higher wear that one gets by bypassing that period of high wear, letting it pass at idle, then driving the car at a slightly cooler temperature at a point on the curve where wear difference really isn't that significant.

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irst i said that the rate is per hour at that temp. no car is going to idle at that temp for but a few minutes.

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second, the reason you take off and drive is to help the engine warm up quicker. i never said anything about how you should drive it just that you should. you should drive it like an old lady.

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Originally posted by sigma:

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irst i said that the rate is per hour at that temp. no car is going to idle at that temp for but a few minutes.

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No, you said that a motor will wear at 0.002 per hour at idle even once its' reached optimal temperature. Assuming that's millimeters (because it can't be inches, a cylinder wall would be gone in a matter of weeks) you'd still wear several mm per year off a cylinder wall -- you'd lose compression within weeks at that rate.

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second, the reason you take off and drive is to help the engine warm up quicker. i never said anything about how you should drive it just that you should. you should drive it like an old lady.

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Yes, but it doesn't make any sense.

When you're driving, even like an old lady, your pistons will still be moving at least 3-4 times faster than they ar eat idle -- therefore you're doing 3-4 times as much damage every second. Even if you could warm the car up 3-4 times faster by driving it, which you can't, the net wear will be exactly the same.

Coupled with the fact that you're doing 2-4 times as much damage (using your numbers) every second when the engine is first started than you are after warm-up, it makes no sense at all to drive it before it's warmed up.

You're advocating doing 3-4 times more damage (engine is revving 3-4 times faster while driving than at idle) while the engine itself (because it's cold) is already doing 2-4 times as much damage to itself as it would be once it was lubed and warmer. The net effect (you're talking 0.008*3*3 for at least a few moments is a HUGE increase in wear compared to the 'extra' damage does while letting the car warm at idle.

Yes, sitting at idle does more instantaneous damage for a slightly longer period of time, but 1> you avoid the added wear from higher engine revs, and 2> you avoid multiplying the wear from that high initial wear due to taking off immediately. The cumulative effect is much lower.

The most efficient combination of speed and wear on the motor is to start it, wait until the revs settle, then drive. Once the revs have settled, you've already bypassed that high-wear period and are at a level that's above, but not significantly above normal operating wear. That's when you drive. Driving immediately puts significantly higher engine revolutions in the time period when you don't want it, and you can't alter the time it takes to warm up significantly enough (or even close) to offset the exponentially higher wear on the cylinders by driving in that time period.

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Originally posted by jtour:

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Originally posted by sigma:

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irst i said that the rate is per hour at that temp. no car is going to idle at that temp for but a few minutes.

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No, you said that a motor will wear at 0.002 per hour at idle even once its' reached optimal temperature. Assuming that's millimeters (because it can't be inches, a cylinder wall would be gone in a matter of weeks) you'd still wear several mm per year off a cylinder wall -- you'd lose compression within weeks at that rate.

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second, the reason you take off and drive is to help the engine warm up quicker. i never said anything about how you should drive it just that you should. you should drive it like an old lady.

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Yes, but it doesn't make any sense.

When you're driving, even like an old lady, your pistons will still be moving at least 3-4 times faster than they ar eat idle -- therefore you're doing 3-4 times as much damage every second. Even if you could warm the car up 3-4 times faster by driving it, which you can't, the net wear will be exactly the same.

Coupled with the fact that you're doing 2-4 times as much damage (using your numbers) every second when the engine is first started than you are after warm-up, it makes no sense at all to drive it before it's warmed up.

You're advocating doing 3-4 times more damage (engine is revving 3-4 times faster while driving than at idle) while the engine itself (because it's cold) is already doing 2-4 times as much damage to itself as it would be once it was lubed and warmer. The net effect (you're talking 0.008*3*3 for at least a few moments is a HUGE increase in wear compared to the 'extra' damage does while letting the car warm at idle.

Yes, sitting at idle does more instantaneous damage for a slightly longer period of time, but 1> you avoid the added wear from higher engine revs, and 2> you avoid multiplying the wear from that high initial wear due to taking off immediately. The cumulative effect is much lower.

The most efficient combination of speed and wear on the motor is to start it, wait until the revs settle, then drive. Once the revs have settled, you've already bypassed that high-wear period and are at a level that's above, but not significantly above normal operating wear. That's when you drive. Driving immediately puts significantly higher engine revolutions in the time period when you don't want it, and you can't alter the time it takes to warm up significantly enough (or even close) to offset the exponentially higher wear on the cylinders by driving in that time period.

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Very well said!

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I R PHYSICS...rawr

Originally posted by KingpinSVT:

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My car seems to take forever to warm up. Maybe 2 or 3 miles before the temp needle even moves. Then it starts to slowly warm up.

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So is mine but it never used to be that way b4. Also the Duratec we got gets warm like within seconds, so when I remore-start my car and it's sitting outside for like 15 minutes and then my wife starts her Duratec - hers gets warmer like 4 times faster...

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The most efficient combination of speed and wear on the motor is to start it, wait until the revs settle, then drive. Once the revs have settled, you've already bypassed that high-wear period and are at a level that's above, but not significantly above normal operating wear. That's when you drive.

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Originally posted by striker2:

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how long does it take your rpms to settle. maybe 30 seconds. if you start your car then turn on your lights and buckle your belt the rpms should have settled. anybody that doesnt drive with their seatbelt on is just a dumba**. and then you take off. thats what ive been meaning when i say just get in and drive it. if your rpms take several minutes to settle then there is something wrong, they should settle very quickly.

desired idle rpm is based off of your coolant temps. its not going to idle properly until it has reached operating temp. the fastest way to reach operating temp is to drive it.

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Whoa, you just contradicted yourself. You say you should wait for the idle rpm to settle and then drive, but in the next paragraph you say that the fastest way to make the car idle properly is to drive it.

Originally posted by Rishodi:

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Originally posted by striker2:

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how long does it take your rpms to settle. maybe 30 seconds. if you start your car then turn on your lights and buckle your belt the rpms should have settled. anybody that doesnt drive with their seatbelt on is just a dumba**. and then you take off. thats what ive been meaning when i say just get in and drive it. if your rpms take several minutes to settle then there is something wrong, they should settle very quickly.

desired idle rpm is based off of your coolant temps. its not going to idle properly until it has reached operating temp. the fastest way to reach operating temp is to drive it.

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Whoa, you just contradicted yourself. You say you should wait for the idle rpm to settle and then drive, but in the next paragraph you say that the fastest way to make the car idle properly is to drive it.

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