I have a question: When I start my car the coolant level in the reservoir is at the "fill to cold" level, however when a drive two or three blocks it is full. Is this normal? It returns to normal after it sits for awhile. Should the radiator cap valve restrict overflow activity until engine gets hot?
So now it's May 7 and 88 deg outside. The car got up to 228 and recovered to around 221-225 once I started driving. However once it reached 235 it slowly climbed to 245. As I was pulling into my garage it had reached 250. There was steam coming out from where the reservoir is, and could hear it bubbling in the bottle. Help! Are my fans not operating properly? Is there still air in my system? Could my water pump be faulty?

 

Yes as the coolant warms up heat expands the coolant and the reservoir level raises
You always want to leave 1 or 2 inches of coolant level below the top--to allow for expansion OR for any air bubbles that may have gotten into your cooling system
These LS engines are prone to having air bubbles in the cooling this will make it run hotter than normal and not allow full cooling
I would try to "BURP" your cooling system and that will get any air out of the system
To BURP the cooling system you can start the engine with the radiator cap OFF --as the temps get up to normal you should see the coolant begin to circulate--Yes it will make a mess ! then re fill--
Finally I always recommend installing a colder thermostat on any LS engine-The stock Thermo begins to open at 195* However it is not fully opened until about 204* Way to late !
Best thing to do is install a aftermarket 160* thermo
Your engine will not run that cold trust me It will run about 185-200* which is wonderful
THEN in return you can have a tuner re-set your electric fans to come on sooner

STOCK Corvette fan settings are
#1 fan ON at 226 OFF at 219
#2 fan ON at 235 OFF at 227
Are you kidding me ??? That is way to late and way too hot !!
Once you install a 160 thermo I would set the fans as such
#1 ON at 202 OFF at 190
#2 ON at 208 OFF at 203
This will make you coolant temps run between 190 and 200--PERECT for an LS
PLUS remember if your car has an auto trans there is a trans cooler built into the radiator So in return your trans will runs cooler as well and it will make both your engine and trans happy !

 

Thanks for the swift and informative response. I will attempt the burp technique that you described. Just to be clear, you are talking about doing this with the "radiator" cap off, not the reservoir cap? How long should I let it make a mess?

 

9) Fill the cooling system through the surge tank.
10) Fill the cooling system with a 50/50 mixture of DEX-COOL® coolant and deionized water.
11) Start the engine.
12) Allow the engine to idle for 1 minute.
13) Install surge tank cap.
14) Cycle the engine RPMs from idle to 3000 in 30 second intervals until the coolant temperature reaches 99°C (210°F).
15)Shut off the engine.
16) Remove the surge tank cap.
17) Start the engine.
18) Allow the engine to Idle for 1 minute. Fill the surge tank to 12.7 mm (0.5 in) above the COLD FULL mark on the surge tank.
19) Install the surge tank cap.
20) Cycle the engine RPMs from idle to 3000 in 30 second intervals until the coolant reaches 99°C (210°F).
21) Shut off the engine.
22) Remove the surge tank cap.
23) Top off the coolant as necessary, 12.7 mm (0.5 in) above FULL COLD mark on the surge tank.
24) Rinse away any excess coolant from the engine and the engine compartment.
25) Inspect the concentration of the engine coolant.
26) Install the surge tank cap.

 

Your car will tell you when it’s low on coolant.

 

You guys are awesome. Thanks to the useful info I was able to properly burp my cooling system. The temp holds steady when driving, no worrisome fluctuations. I check the coolant reservoir daily and it also appears to be holding steady. It reads just below the"fill to cold" mark. So I top it off and hit the road. Thanks for the advice!