My '96 suburban is still relatively new to me. I towed with it for the second time today. And it overheated for the second time! The radiator had been replaced in September. I don't think that the system had been properly burped. I thought that I had the cooling system burped after the first incident. I must not have had the cap properly screwed on the overflow tank, because it erupted after a long 5% incline. -this one was clearly my fault.

That's the background. Now here's the problem. I think I have the air out of the system. The overflow tank has fluid. However, the low coolant light is on. And I'm not 100% sure that the cooling system is properly burped. Anybody have any ideas? -Joi

Only time I've seen the overflow tank full, and the Low Coolant light on was because the overflow tank was full of water, which could explain your overheating problem too.

If you do have the proper ratio of coolant in the system, then its probably a failed sensor. Is there any carbon buildup in the overflow tank? I would try replacing the thermostats first, then the water pump if you don't see any signs of cracked head or blown head gasket.

I think you should run a compression test. I just had to remove my head and what a difference in temps. after.

I agree with QM, a low coolant light is a bad thing. I wouldn't be surprised if you have head gasket damage, and are consuming coolant.

HEY HEY NOW, A low coolant light may or may not be a bad thing. IF you are using coolant and the low coolant light does indicate the fact that you are low on coolant then you need to investagate and find the reason, BUT, as in my case your light is on and has always been on and nothing is low nor does the sensor appear to be bad, AS I am told they go bad often, then it is just a pesky light that won't go out. I think, but can not confirm that it goes thru the PCM and I guess I just got a bad wire somewhere. I'll find it someday when I ain't looking for it I guess.

Thanks for the input. Does the low coolant light need to be reset after it goes on? I see the wires that lead to the overflow tank. There's definitely enough coolant, but the light stays on. Is this by any chance a ploy by gm to get me to bring my truck to the dealer ship???

Your 96 may or may not have the later cooling components. Late 96 trucks have the dual thermostat housing and a High Output water pump. You can see a HO on the top of the pump.

The best thing you can do it to make sure you have the above to start and then start to improve the performance by replacing the highly restricted exhaust system. The next step for cooling would be to get the 9 blade fan and you will have to change the fan clutch as the new fans have a 4 bolt pattern and the 96 has a 6 bolt pattern. This will make a big difference in the performance. I have adjusted the stock fan clutch spring to allow the fan to cut in at 195 to 200 deg instead of the 220 it normally does.

I have a late 96 and will be changing to the larger fan this year. I have a Heath reprogramed ECU and the Heath mechanical wast gate controller to allow me to have more boost. It doesn't do much good to up the boost much if you can't get more fuel. Pulling a 8k trailer I ran into the same things you did on similar grades in NC. I have picked up 20 mph on the grades but still get a little heatup when pushing it up the steep hills

Did you have coolant in the overflow tank before the low coollant light came on? If the tank was at normal levels and the light came on it may just be a bad connection at the radiator. Mine will signal low coolant many tiomes when I first start up but the light goes out as soon as the engine warns up.

You say the radiator was replaced but did they clean the outside of the AC condenser and the oil cooler radiators? Take a look at my web page to see what collects behind the oil coolers and in the front of the condensor.

Two things:
How big is this thing you are towing?
What does your tach read at 65 mph? (4.10 rear is great for towing)
At cold start, is your coolant hose getting pressurized before the engine gets warmed?

Okay, maybe three. . .

1. Too much, too heavy, with too little cooling (like pre-97's) may get toasty.
2. Too high rear gearing, great for mpg, but not good for towing.
3. Getting pressure in system before it's warm indicates combustion products entering cooling system. That means head gaskets, etc. (I think that there are air bleeders in your system, I don't know, I've got the van) Make sure all air is out. Water pump I don't *think* will pass the air.

i don't know if your coolant level sensor is the same as a '94, probably is. i got tired of the light so i jumped the two leads together with a short piece of wir and that keeps the light out.

your thermostat might be broken in the closed position or not fully opening allowing hot coolant to keep recirculating in the block till it overheats.

I've once seen the low coolant light suddenly come on on mine two or three times though there was enough coolant in the overfill tank. The light stayed on for 10 minutes or so and went out again. Probably some moisture had built up somewhere and made the light come on. It didn't come back yet.

The cooling looks to be sufficient. The a/c condensor and tranny cooler were replaced along with the radiator. I was only towing about 4k. I had kept it out of overdrive with top speed of 45 mph. The 'burb has the higher gear ratio so it definitely feels like a heavier load. The air filter doesn't look so good either. I suppose it was a combination of the above. I still want to figure out the low coolant light. I'll try jumping the sensor wires and see what happens. Thanks again for all the input.
-Joi

Check the coolant cap and heater hose disconnect for leaks. The system doesn't keep it's cool unless it holds pressure.