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Re: 2 cooling fan questions Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 9 Apr 2003 17:18:13
In Reply to: 2 cooling fan questions, JJ, Wed, 9 Apr 2003 16:30:39 Members do not see ads below this line. - Help Keep This Site Online - Signup |
A radiator needs moving air to remove the heat. The fans come on to provide airflow when the car isn't moving. Even a new radiator isn't going to change the fact that moving air will carry off heat better than still air.
An 82C fan switch means that the coolant in the radiator won't get as hot. This is a Good Thing. If you didn't have this, it makes the 82C thermostat only half as effective:
When the coolant in the engine reaches 82C, the thermostat opens and ports coolant to the radiator; hopefully cooler coolant comes back. If the radiator still have an 89C fan switch, the coolant in the radiator would be running around 89C. The thermostat would open, but in some conditions it would actually be getting coolant BACK from the radiator hotter than it sent out.
If you have an 89C fan switch and a 82C thermostat, and the car is just sitting and idling, the engine coolant will get no lower than 89C.
When you're moving, the fans don't usually come on, because the airflow from moving does the trick.
OK, why keep the fans on when stopped? Actually, it doesn't help that much. But it does help. First, just because the water pump isn't turning doesn't mean the flow has stopped. If the radiator is cooler than the engine, and the thermostat is open, there will be some thermonic pumping. Don't think that works? Early Saabs didn't have water pumps, and relied on this for coolant circulation. Works like crap, but there will be some movement.
When you shut the engine off, the temperature rises because (1) the car isn't moving, or shouldn't be, and (2)flow is down. That airflow helps keep the coolant temperatures reasonable - otherwise you could actually boil over some.
Lastly, that airflow goes past the radiator and over the engine, pulling some heat from the block.
The 'after shut-off' fan running doesn't help much, and many folks have disabled it, as the time-delay relays stick closed and run batteries down. Even Saab recognizes this and has a service bulletin to kill the time-delay. But it does help some.
posted by 192.249....
, Wed, 9 Apr 2003 20:18:07, Wed, 9 Apr 2003 21:45:13, Wed, 9 Apr 2003 17:18:13 <-- Viewing This Message
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