I working on the wife's 1994, runs hotter than it really should at times. Twice last week when she was stuck in traffic the digital readout was at 255 and the analog over 260. When driving the digital drops to about 237 or so.
Check for clogged radiator/condenser
Primary fan turns on at 225, secondary turns on around 235
Fans turn on when AC is on
New Water Pump last year, and T-Stat
Now when I check for coolant recirculating on my 84 I just take the radiator cap off and watch

On the LT its a bit different due to the location of the cap, When my T-Stat opens will I see the coolant recirc in the reservoir?

Is there... or could someone point me to the link on how to bleed the coolant system?

thanks

 

Air trapped in the cooling system might be the way to start...
Try the search option or someones should chime in with the link...

 

I'm guessing T-stat at this point. As I started the car and let it warm up. Temp got up to 221 and the coolant level never went down, just a couple of bubbles. The T-stat is LT specific but I'll go pick another one up and see if it works.

 

I plan to test the Tstat prior to buying another

Surge Tank is filled to the top and nothing is in the overflow tank, neither cold or hot

 

your temps are high. you should be running close to what your stat is rated at on the open rd. If you are sure of the fluid levels I would start with the stat also.

 

Are you sure you have cleaned the radiator fins very good? I did this several time with the stock radiator it would help a bit but I could really never get all the little grit out of the fins totally. You bang that thing on the garage floor for hours and still get **** out of it.

After replacing my radiator, any higher than usual temps that I had periodically experienced went away.

 

Open the radiator and make sure it is full. Then on the tstat housing there should be a brass bleeder screw/nut open it until coolant comes out then tighten the bleeder screw, fill system and tank to cold level.

Also use a towel under the tstat housing to keep coolant away from the opti and some say to do it at operating temps so the stat is open.... If I remember an LT1 stat has a bleed hole in it so it should work when cold.

 

At this point this is what I've done.
Tested the Tstat- opens at 190 tho it says its 180 stat. Margin of error maybe..not to worried about that.
Filled the overflow tank, ran the car at idle, bleed the lower hose rad bleeder. Once I saw the level moving a little bit at the neck of the surge tank I closed it up. Primary fan turned on at 228 and only cooled till 223 at idle. Primary fan still running.. didn't cool it enough to turn off.

If this doesn't work I'll try the cap next.. Its a 15lb cap.

 

Does your heat work?

 

My 92 had two bleeder screws; one on the thermostat housing and the other was on the throttle body. Did GM delete the TB bleeder at some point?

Because the bleeder screw is designed to get rid of air pockets, there should be no real need to "pack" the cooling system. But it's something that can be tried.

Fill the system with the bleed screw open. Once coolant begins to flow out, close the bleed screw. Finish filling the tank until the coolant level is just below the filler neck. Start the engine and let it idle until the coolant drops (t-stat opens). Run the engine at 1100-1200 RPM or so and continue filling coolant until it's at the base of the filler neck. At this point, you should see some coolant flow in the tank if everything is working OK.

Install the pressure cap, drop the RPM's to a normal idle. Check the fluid level in the overflow container and fill to the COLD mark.

Another possibility is a bad lower radiator hose. Old hoses can get weak and if it has a spring in the hose, it's possible that the spring is broken or simply rusted away. If the hose collapses, that reduces the flow rate leading to higher coolant temps. If the car still has the original hoses, it might be a good idea to replace both of them.

Also, have you done a full flush of the cooling system? The FSM says to remove the knock sensors at the bottom of the block to get rid of any sludge that has built up. It's sort of a PITA to do, but if coolant isn't circulating everywhere, temps can climb. Same with the radiator; if the tubes are clogged up, there won't be enough area for the coolant to flow and let temps drop.

The FSM Says to use water only for flushing. The procedure says to drain the coolant, refill with water, run the engine to operating temp, drain and repeat two more times (each time draining the block by removing the knock sensors). Then finally fill the system with a 50% mix of coolant and distilled water.

 

Obviously the temps are too high. Since you seem to have verified the thermostat is operating correctly - I'd suggest:

1) Check / Replace Radiator Cap

2) Double Check that the Upper and Lower Rad hoses are in good condition and are not collapsing. If the Hoses are more than 5 years old - It's probably time to replace them. A Upper Rad hose failure will likely get the opti wet - which will kill it - which is a $400+ part and at least 3 hours of time to replace ....

3) A full cooling system flush - including removal of the 2 knock sensors, and flushing out the heater core and coolant reservoir (I bought my 92 Used, and after one lap on the track the cooling temp was over 230 and climbing - quickly). You wouldn't believe the crud that came out of the block when I pulled the 2 knock sensors out - the coolant in the overflow tank looked nice and green, but the "coolant" that came out of the block when I pulled the knock sensors was dark brown - not green).

4) Remove radiator (it's not a terribly fun job, but it's not anywhere near as bad as pulling the tranny). A lot of road "dirt" etc. gets up in there and the only real way to get it out is to get the radiator out and hose / lightly brush everything out of it. While it's out - see how well it flows. If the cooling system has not been maintained, the radiator could be partially plugged up. You can do this yourself - or take it to a radiator shop and have them flow test it.

Those steps should solve most any cooling system problem.