Single Fan for Engine Cooling and Airconditioning

[TimV]

When the AC is turned on, the belt driven fan goes on. And when there isnt enough air flow, the 2 electric fans kick in to.

The fans are in front of the ac radiator, behind that radiator is the coolant radiator, and between the coolant radiator and the engine is the belt driven fan.

[bobdbilder]

Originally Posted by Piwoslaw

My P307 has A/C (the condenser is right in front of the radiator) and only 1 fan. The fan kicks in when the coolant temperature reaches 98C. If A/C is active, then the fan keeps coolant temperature below 82C, which is a bummer if you are trying to keep the engine running hot for FE

You might be mistaken. What regulates the engine temperature is the thermostat. This closes during engine startup. Typically the coolant temp sensor situates close to it. It opens mechanically when a preset temperature is reached. The radiator and fan reduces coolant temperature.

Bear in mind that this singular fan setup also need ventilation of the engine bay. In a different discussion, this was researched by Dr. Karmann and was used to modify airflow around the windshield. A small engine compact car may achieve this by simply removing the weather strip or seal where the windshield meets the hood. Leaving a small strip where fresh air inlet is so that engine heat might not enter the cabin.

Bigger engines with different layouts may require bigger sized outlets. I seem to recall side air vents were in fashion at one time. This time it could actually be useful.

[Piwoslaw]

Originally Posted by bobdbilder

You might be mistaken. What regulates the engine temperature is the thermostat. This closes during engine startup. Typically the coolant temp sensor situates close to it. It opens mechanically when a preset temperature is reached. The radiator and fan reduces coolant temperature.

The t-stat is what allows engine coolant into the radiator, but once it is there the fan can be used (if there is not enough airflow) to cool it, of course no cooler than the t-stat's closing temp. In my case the coolant temp stabilizes at 78C, so this is the t-stat's opening temperature. I've seen the ECU's documentation, which is where I got the limiting temps from. These were confirmed on the road (ie when A/C is active the fan kicks in when coolant temp goes above 82C, without A/C this is 98C). I like to run my coolant temp around 90C, as the engine has slightly lower FC.

[bobdbilder]

I think there are two ways to go about this.

A) plug an orifice plate of smaller size just after the thermostat, effectively reducing flow of coolant to the engine or

B) modify the signal from your temperature sensor using a potentiometer as a voltage divider as in this Autospeed article. AutoSpeed - Pots aren't just variable resistors

[cRiPpLe_rOoStEr]

Originally Posted by Piwoslaw

My P307 has A/C (the condenser is right in front of the radiator) and only 1 fan. The fan kicks in when the coolant temperature reaches 98C. If A/C is active, then the fan keeps coolant temperature below 82C

Maybe that explains why my stepmother claims her 206+ "overheats" with the A/C off

[user removed]

Originally Posted by bobdbilder

I think there are two ways to go about this.

A) plug an orifice plate of smaller size just after the thermostat, effectively reducing flow of coolant to the engine or

B) modify the signal from your temperature sensor using a potentiometer as a voltage divider as in this Autospeed article. AutoSpeed - Pots aren't just variable resistors

Radiators are designed for the "worst case scenario". Think 124 degrees stuck in traffic in Phoenix AZ in July.

Now think about -40 degrees (C or F=same temp), you have 5 times the radiator you need to keep the engine cool. In fact it's almost impossible to keep the engine at operating temperature, so like the big rig drivers, block the airflow over the radiator to retain heat energy, until the coolant exiting the radiator is the same temperature as it was in July (probably impossible when it is that cold).

Adding any restriction to coolant flow does not address the grossly excess radiator capacity when ambient temperature is 164 degrees colder (124 vs -40).

regards
mech

[MobilOne]

My 1960 Volvo 544 had a curtain one had to pull up in front of the radiator to get the engine warm in the winter. It didn't work very well.