I just bought a 1998 c5 with a 18500 miles and the car seems to be running hot at stoplights. I'm get a 20to30 degree temp change in just a few minutes. Is there any way to program the ecm to turn the fans on at a lower temp?

 

First I would crawl under the car and look up into the area between the radiator and a/c condensor to make sure there is nothing blocking airflow. Sometimes plastic bags, etc., get sucked up there.

If the area is clear, you can have the PCM programmed to turn on the fans at a lower temperature.

HTH

 

What are your temps? Without the air on, the fans don't come on until your coolant reaches 225F. So if you run down the road the airflow will keep your car at about 198F, when you stop the temp will go up to 225 before the fans come on and then it will drop. Equally when you drive off again the temp will go down below 200F again.
All perfectly normal!!

 

How hot is it getting???

You can always buy a 160 degree T-stat.

 

I too beleived my car was running a little hot when I first got, so I looked into it.

Here is what I came up with:
LS1's run hotter than average engines. This is perfectly normal - GM designed them to run this way. Coolant temps reaching 220's is normal, and is this is where the fans will turn on to bring temps down. Furthermore, the fans are programmed to turn on when the A/C is turned on. Because of this - many times when I stop at a long light, or am in stop in go traffic I will turn the A/C on low so that the fans will maintaining coolant temps between 190 and 200.

Regarding a 160* Tstat, I would keep with stock or 180* Tstat.

A basic piece of info that many (but not all) people know is that engines have optimal running temperatures. Too cold and increased wear, too hot and increased wear. The Tstat aids the engine in warming up faster aswell as running at appropriate temps in colder temps where coolant temps may be too low with continually flowing cooling system.

What some do not know is that engine temperatures do need to occasionally increase to temps that usually a 160* Tstat will not allow the engine to do. This is because the engines needs an occasional increase to boil out (turn from a liquid to gas) certain liquids that can accumulate in your oil. I'm not saying that this can't happen with a 160* Tstat, its just harder/less frequent for it to.

To answer your exact question: a 20 to 30 degree increase in coolant temperatures in a few minutes is perfectly normal for your LS1. I wouldnt worry about it as long as your coolant temps don't reach much over 230* and that your car does cool down after reaching these "elevated" temps. A quick inspection to make sure there is no blockages (or plastic bags), the radiator appears to be normal, and that you have adequate amounts of water or coolant in your radiator and reservoir as suggested by coast7 is always a good idea (easy to do and good results ).
Yes your computer can be programmed to turn the fans on earilier. An easier/alternative to this is to turn the A/C on (any setting) and/or turn your heater on(as recomended by auto manufactorers and seen on king of the hill lol. Keep in mind if you turn the A/C on with heat selected warm air will still come out it will just be "air conditioned" warm air (dehumidifying the air is on of the aspects your A/C does).

I'm sure this will help you as I probably gave you more information than you wanted to hear. If you or anyone else has any other questions feel free to PM me.

 

Thank you for the info

 

160 thermostat is 'minimum' temp, not max temp 'at idle'. Temps are kept up for emissions reasons,keeping unburned hc down in combustion chamber