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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Tue, 1 Nov 2005 05:09:55 Share Post by Email
In Reply to: Re: Help: Thermostat replacement questions, Jesse and his Champ, Mon, 31 Oct 2005 12:54:09
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Yes, only coolant coming out after 15 minutes, not air.

The thermostat/thermofan switch system is somewhat disconnected. The thermostat opens at a given temp (say 89C), letting hot coolant out into the radiator - this flow causes (hopefully) cool coolant in from the radiator. Once the car warms up fully, the thermostat will be slightly open, allowing a small but constant flow of coolant to the radiator, where the air flowing over it cools it down, and back it comes to the engine. How open the thermostat is depends on engine load, outside air temp, and how much of that air is flowing over the radiator.

The temp gauge shows the temperature of the coolant in the engine.

The fan switch doesn't give a hoot about the engine temp. It monitors the radiator temperature. If the radiator gets hot, the fan(s) kick on. Why would the radiator get hot? No airflow. The fans are there to provide airflow when the car isn't moving, or moving very slowly. By the time you get to about 30 mph, the airflow is as much as or more than the fans can provide.

But the engine is the heat source, and there is a lag getting to the fan switch. So the engine gets hotter and hotter, and then the radiator gets hotter and hotter, and eventually the fans come on. So the engine gets pretty hot before the fans kick in. If you put in a cooler thermostat, it will have a small effect - the thermostat will open fully sooner, providing more flow to the radiator, so it will get hot faster; the fans come on and cool the radiator. So you'll see a small drop in max temp in traffic with just a cooler thermostat.

The best bet if you're running hot in traffic is to have (1) a regularly flushed, clean cooling system, (2) unclogged radiator, and (3) lower temp thermostat and thermoswitch. I say the first two first, because a compromised cooling system won't get fixed by cooler thermostat/switches.

The fan switch helps because it gets the radiator cooling at a lower temp, so the overall system temp will be lower. In the old days (say a '74 99), we would use a spare switch space in the dash, and put in a switch that would kick the fan on manually. In fact, my '67 two-stroke Sonett has a switch from the factory that turns the radiator fan switch on, in parallel with the thermoswitch.

Outside air temp has something to do with engine temp, but you can still overheat a car at below zero temps. And with cars that are getting to be 17 years old, radiators get old and clogged. If the car hasn't been having regular coolant flushes, that may be the problem.

As to thermostat location on an '89, the easiest thing to do is grab that big upper hose and follow it back to the engine. Where it stops is the thermostat.

posted by 192.249....
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