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Old 16th October 2016, 21:03   #106
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

At a recent drive, I had to put the car idle for ~30 mins at two instances. On first I didn't try, but second time, I simply left the hood open. The 2200CC MHawk was barely audible with the hood open. Maybe while idling, if I can, I may leave the hood open.
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Old 16th October 2016, 21:40   #107
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

There is no need to try and cool a car just because it "feels" hot. Unless the temperature gauge is in the red or the high temp warning light is on, only then do you need to take some measures to cool it. Usually turning on the heater with fresh air mode should do the job just fine.
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Old 16th October 2016, 21:54   #108
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

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Originally Posted by sudev View Post
Thinking again.

Cooler engine is prone to wear. Why? All engine components are sized to work best at optimal engine temperature. So the rings, pistons, valve stems, valve seats etc. Would have expansion margins to suit working at optimum temperature.

So if we are on continued journey cycle why cool the engine more than needed when it has to heat up again to optimum temperature?

Have I stirred a hornets nest? Guru's opine please.
Whether you have stirred the bees nest or not, this is fact and no two ways about it. Cars are designed to run between 98 degrees and 101 degrees centigrade and that is why we should change the pressure caps regularly if there is water loss. The spring inside the pressure cap maintains the temps at about 101 degrees in association with the cooling fan and sensors. If the temps drop to 98 then it is time to change the pressure cap.
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Old 16th October 2016, 22:12   #109
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Originally Posted by drpullockaran View Post
Whether you have stirred the bees nest or not, this is fact and no two ways about it. Cars are designed to run between 98 degrees and 101 degrees centigrade and that is why we should change the pressure caps regularly if there is water loss. The spring inside the pressure cap maintains the temps at about 101 degrees in association with the cooling fan and sensors. If the temps drop to 98 then it is time to change the pressure cap.

Pressure and temperature are two different things. Pressure doesn't control temperature, but it does affect the boiling point of your cooling liquid.

Jeroen
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Old 17th October 2016, 20:40   #110
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

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Originally Posted by autodoctor View Post
Still, if the engine temperature goes above the fan trigger limit, it will activate the normal cooling fan.
That's the reason i wanted to try manually activating it, when i turn A/c ON instead of fan spinning in slow speed (starts in slow speed in cold temp), i witnessed radiator fan kicking in full speed, once i tried by turning off the A/c immediately expecting the fan to also cut off too, considering the fact, activation temperature is not reached, but after turning off A/c, the fan ran for a three full minutes before cutting off, bringing to a logical conclusion that the fan was spinning only to cool the coolant and not the condenser, do you have a explanation on this behavior, if not for the A/c why should it spin that long a duration, is there a malfunction here.

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Originally Posted by autodoctor View Post
Remember even though an electric fan blows air to the cooler, it indirectly puts load on engine (via alternator charging the battery).
Agreed.

Last edited by sriramr9 : 17th October 2016 at 20:56.
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Old 17th October 2016, 21:44   #111
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

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Originally Posted by sriramr9 View Post
That's the reason i wanted to try manually activating it, when i turn A/c ON instead of fan spinning in slow speed (starts in slow speed in cold temp), i witnessed radiator fan kicking in full speed, once i tried by turning off the A/c immediately expecting the fan to also cut off too, considering the fact, activation temperature is not reached, but after turning off A/c, the fan ran for a three full minutes before cutting off, bringing to a logical conclusion that the fan was spinning only to cool the coolant and not the condenser, do you have a explanation on this behavior, if not for the A/c why should it spin that long a duration, is there a malfunction here.



.
Electronic Fan control is a complicated function as it take lots of inputs.
For eg: in this scenario you probably had the car driven on a hot day and you are doing all these while you are stopped?
if that is the case your engine temperature have just crossed the cooling fan activation limit, hence triggered the fan. No i don't expect any fault.

Or by activating A/C, it exerted Load to engine and activated the fan as it could raise the engine temp.

Some controls activate both fans as an added precaution.

Regarding using the heater to cool engine: Yes it is true. Because the heater uses the coolant circuit to give hot air. So you are transferring the heat from the coolant to the cabin.
But on a hot day, it is not fun to do so though
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Old 18th October 2016, 00:14   #112
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

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Originally Posted by Jeroen View Post
Pressure and temperature are two different things. Pressure doesn't control temperature, but it does affect the boiling point of your cooling liquid.

Jeroen
Yes, you are right, but there is a very definite correlation between the cooling system pressure, and maintaining the coolant temperature. In newer cars, mainly because the pressure controls the flow of the coolant in different ways.
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Old 18th October 2016, 00:50   #113
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Default Do we need to keep the hood up to cool the engine after a long drive?

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Originally Posted by dhanushs View Post
Yes, you are right, but there is a very definite correlation between the cooling system pressure, and maintaining the coolant temperature. In newer cars, mainly because the pressure controls the flow of the coolant in different ways.

No, it doesn't as such. Again, the reason to keep the cooling liquid under light pressure is to raise the boiling point of the liquid.

The temperature, in essence, is controlled by means of the thermostat. Higher temperature gives you higher pressure. The pump contributes to the pressure, but as most cars operate with closed loop cooling system inlet and outlet pressure its not really a factor. (Of course on an open loop system the pressure is atmospheric).

Jeroen

Last edited by Jeroen : 18th October 2016 at 00:56.
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Old 18th October 2016, 15:00   #114
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

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Originally Posted by autodoctor View Post
Electronic Fan control is a complicated function as it take lots of inputs. Some controls activate both fans as an added precaution.
My car is equipped with only one Fan and upon Activating A/c is starts spinning immediately at slow speeds during cold starts.

Quote:
Originally Posted by autodoctor View Post
Because the heater uses the coolant circuit to give hot air. So you are transferring the heat from the coolant to the cabin.
Unable to understand the context here, could you please enlighten with an example ?
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Old 18th October 2016, 15:35   #115
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

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Originally Posted by sriramr9 View Post
My car is equipped with only one Fan and upon Activating A/c is starts spinning immediately at slow speeds during cold starts.



Unable to understand the context here, could you please enlighten with an example ?
The heater matrix has hot coolant running through it.
Heater matrix
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Old 19th October 2016, 13:19   #116
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

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Originally Posted by autodoctor View Post
Regarding using the heater to cool engine: Yes it is true. Because the heater uses the coolant circuit to give hot air. So you are transferring the heat from the coolant to the cabin.
But on a hot day, it is not fun to do so though
i was taking this test, cranking the temperature down to 20 degrees in AUTO mode making sure chilled air is routed to cabin and with the basic understanding that there will be two explicit signals that could turn ON the fan, One is the engine temperature, the other being refrigerant pressure in the air con system, (fan running to pull some air through the condenser).

As you mentioned, the heater core is part of the thermostat circuit & in my test i opted for chilled air & did not try to use hot air for cabin, (not activated the fan of the heater matrix).

My basic point for this exercise was to see if force ventilating the radiator before cut in temp really helps or not ? You say it does not matter, is my understanding correct ?

But still the fan spinning in high speed mode after turning off the a/c is still puzzling as to what could be input which kept it live that long a duration if thermostat is not needing that ventilation other wise ?

Last edited by sriramr9 : 19th October 2016 at 13:23.
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Old 20th October 2016, 04:14   #117
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Default Re: Do we need to keep the hood up to cool the engine after a long drive?

Hi Sriram,

Force ventilating will not help in reducing heat, especially when you have your A/C turned ON to give you high cooling inside your cabin (as it exerts more load to engine). I personally wouldn't do this.

Also, since your car have single electric fan, makes it bit more complicated to explain.

One more thing is, something called 'heat soak'. When a car is been driven for some time and stopped, the engine temperature can increase. This is due to the lack of air flow through radiator. At these situations, the fan will come ON to aid cooling.

Here in Europe, i have used cars with out a working fan. On normal driving no issues with out a cooling fan. Only problem is when there is traffic- jams/ stop start traffic, the vehicle over heats! The best thing to do in these situation is switch on heater inside your cabin, helps a bit.

New generation cars have On Board Diagnostics. if there is any issue with a system, It should give you a fault code (aka P Code). The code can be checked by dedicated tool normally from dealer or some after market scan tools.



Hope it helps

Kannan
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