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Old 05-19-2009, 08:43 PM   #1
jonnycube
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Default Radiator fan activation threshold

  • It is hard on a Saturn engine to run when the temperature gauge is over 1/2.
  • Saturns are designed so that the radiator fan turns on when the temperature gauge reaches 3/4.
Why would the car be designed this way?

To deal with this, I know I can install a manual fan switch. Is there a way to change the point at which the fan automatically turns on? Is this a function of the PCM, and if so, is it possible to reprogram it?

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Old 05-19-2009, 09:25 PM   #2
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Default Re: Radiator fan activation threshold

Quote:
Originally Posted by jonnycube View Post
  • It is hard on a Saturn engine to run when the temperature gauge is over 1/2.
  • Saturns are designed so that the radiator fan turns on when the temperature gauge reaches 3/4.

Who says? You?? I'd be willing to bet the engineers that designed the engine and the car know how to make it run at optimal performance. The fan is designed to come on at 226 degrees, and there are plenty of Saturns out there with well over 500,000 miles on them running this way, the way they were designed to run. Stop watching your temp gauge and just drive the thing already. No need to re-engineer the car, it was done right the first time.

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Old 05-19-2009, 09:33 PM   #3
jonnycube
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Default Re: Radiator fan activation threshold

I read it on this forum that Saturns run optimally near the halfway mark on the temperature gauge. I'll see if I can find the post; I'm pretty sure I read it recently. In any case, if a higher temperature is better, than why wouldn't the car be designed to run that hot all the time?

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Old 05-19-2009, 09:40 PM   #4
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Default Re: Radiator fan activation threshold

You are a bit confused.


For the 95 and OLDER car all gauge readings will be 1/8 higher. In traffic or when moving slowly in hot weather the gauge will tend up to 1/2 or above in the 96 and newer cars but not turn on the fan. This is not a problem or an item of concern. The region of operation will read 1/8 higher for the 95 and older cars also. And its still not a problem.

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Old 05-19-2009, 09:44 PM   #5
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Default Re: Radiator fan activation threshold

"When the engine is cold, components wear out faster, and the engine is less efficient and emits more pollution."

"The engine runs best when its coolant is about 200 degrees Fahrenheit (93 degrees Celsius). At this temperature:

The combustion chamber is hot enough to completely vaporize the fuel, providing better combustion and reducing emissions.
The oil used to lubricate the engine has a lower viscosity (it is thinner), so the engine parts move more freely and the engine wastes less power moving its own components around.
Metal parts wear less."

I believe the oil also has a tendency to form acids and sludge at lower temperatures. Lower temperatures are not ideal, the fan keeps the coolant from boiling over (when there is no airflow). Also if the fan came on earlier than it did, it would be running at every stop light, and that takes up gas.

Last edited by BlackPlastic; 05-19-2009 at 09:50 PM..

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Old 05-19-2009, 09:52 PM   #6
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Default Re: Radiator fan activation threshold

All right, thanks guys. I must have misunderstood something along the way. It looks like it's unanimous that my post doesn't make much sense.

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Old 05-19-2009, 10:09 PM   #7
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Default Re: Radiator fan activation threshold

You have an early and late car so if you compare them then make the 1/8 adjustment. Also the front end is a bit different in design so the natural air flow through the radiator is different and that makes the temp gauge respond differently.

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Old 05-20-2009, 07:51 AM   #8
jonnycube
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Default Re: Radiator fan activation threshold

I'm not actually having a temperature issue with either of my Saturns. I just thought that, assuming 1/2 gauge (or thereabouts) is optimal (which I will no longer assume), why wouldn't the fan be programmed to keep it there? Why would it wait until the car got a lot hotter before cooling it back down to the temperature that it normally is? I think that my original post either wasn't clear, or it had a false premise.

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Old 05-20-2009, 08:17 AM   #9
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Default Re: Radiator fan activation threshold

Natural air flow across the radiator and the thermostat control the normal range of operating temperature on the low end and the fan controls the top of the operating range. The low end is maintained at about 195F or slightly above by this method. This temperature is the temperature at the intake of the water pump. The fan switches on at about 222F-226F(cylinder head outlet) and switches off after dropping temperature 10/12F. There is a heat gain across the engine depending on load. When the natural air flow is no longer capable of removing this heat then the fan switches on to maintain temperature.

Overheating is the condition where the fan can no longer terminate or control the increase in temperature.

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Old 05-20-2009, 10:48 AM   #10
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Default Re: Radiator fan activation threshold

The fan turns on other then when checking codes? Huh. You stop too much

~1/2 guage on '91-'94('95?) is the same numerical temperature as 1/4->3/8ths on the '96+.

...
The proper way to fix a S-Series automatic is to replace it with a 5spd O:)

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Old 05-20-2009, 11:09 AM   #11
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Default Re: Radiator fan activation threshold

OT but a lot of the newer cars have dampened gauges that are driven by the ECM so you don't panic after going up a mile-long hill by temporary spikes. Scan tools tell the real story.

Saturn got rid of the oil pressure gauge after 92, and a lot of other makers dumbed them down. Ford explorers have "normal" and "bad" which is the same as an idiot light! People were freaking out to see 60 PSI (pegged) all the time then have it dip to 20 PSI at hot idle.

My impression of the 226 fan rule is to somehow cheat at a pre-prescribed EPA city drive cycle. A manual fan won't overcool as long at the thermostat is working correctly and it means less heat stress cycles on head gaskets etc. You start losing ignition timing before 226 degrees and the cars are dogs, say, when you sit through several city blocks of traffic lights then suddenly are on an interstate onramp gunning it.

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Old 05-20-2009, 12:45 PM   #12
DonP
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Default Re: Radiator fan activation threshold

Oil pumps are essentially of positive displacement devices aren't they? Designed to pump a volume of oil that is based on engine RPM. The thus the pressure is what it takes to push that (RPM dependent) amount of oil through the system at the oil's viscosity.

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Old 05-21-2009, 11:50 AM   #13
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Default Re: Radiator fan activation threshold

Yes but they put the oil pressure sender upstream of most opportunities for the oil to leak out and use up the pressure. When it's colder and thicker it pushes against the walls of the oil galleys fighting harder to get out = higher pressure.

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Old 05-21-2009, 02:27 PM   #14
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Default Re: Radiator fan activation threshold

In theory, the best place for the pressure sensor is arguably where it will detect lack of adequate flow/pressure at the earliest time; i.e., oil pressure not reaching the furthest points (pressure/and flow wise) from the pump.

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