Thermal issues, aka over heating question
 

I'm sure it's something real simple, and hopefully someone here can help. I've been having over heating issues since the Power Tour. LS7, twin e-fan Be Cool radiator. Gauge is showing 250 degrees after idling five minutes. Fans are running and temp keeps climbing. The funny part is the lower hose and lower part of the radiator aren't hot at all. There are some black flecks in the anti-freeze. Bad water pump? Thermostat? Air bubble? The cam was swapped to a milder one before the tour.

Sounds like a gauge problem.

Cold spots on radiator body usually indicate an area where coolant isn't flowing through, as in a blockage. Are hoses building pressure? What water pump are you running?

Have you opened the system recently? A quick heat up at the sensor can sometimes come from an air pocket.

Are hoses building pressure? What water pump are you running? I can squeeze the hoses when it's running. The upper one is hot, the lower hose is room temp after 5 minutes of idling. Not sure if I should be able to or not? The pump is the Wegner accessory drive water pump. Less than 3,000 miles on it.

Have you opened the system recently? Yes, the cam was swapped out before the Power Tour. Never had an issue before that.

Could the thermostat be sticking or bad? Never looked at an LS thermostat, but there are flecks of black rubber in the radiator.

You might have a gauge or sending unit issue. Never seen a LS get to 250 that fast idling. One hose should be hot @250.

Borrow a thermometer and verify temperature.

Then get the air out of the system.

Is the best way to get air out of the system to jack up the front of the car and run it with out the radiator cap? Should I do this a couple of times over a few days? I don't mind buying a tool if that's what I need...

Do you have an overflow with a return? Do you have steam vent return plumbed?

The thermostat most likely isn't the issue. Steam pockets are more likely. Had this issue on my LS3 480HP --- and I spent 3 days tearing into it.... the culprit was no overflow tank and every time it warmed up - and cooled down - it sucked in air which eventually built up and created a steam pocket. That AND the fan was running slow.

I'd check your voltage at the fans and make sure they're cranked up -- this would show up even if you had a 20% voltage drop - say the alternator is cranking out 14.2V and your fan is only seeing 12V...

There have also been some issues with the water pumps loosing their impellers -- they have broken off right at the shaft - so the pump is turning but there's no water circulation. You should be able to see water circulating in the radiator.

do you have the air bleed tube hooked up?

and what greg said. also ls is not a reverse flow system. something i learned with gregs issue.

LS water flow is IN to the motor from the bottom hose towards the thermostat -- and OUT to the radiator at the top hose.

It's easy enough to check flow with a infrared temp gun.... or even using your hand and feel the hoses. Also use the gun to check for temperature DROP from the top (inflow) and bottom (return) --- on in the case of a crossflow radiator -- side to side --- This should drop 20* or so at idle with the fans running.

Use the gun to check front and back of both heads - near the steam vents (I'm assuming your particular LS model has these).

You can also "crack" the seal on these vents (they're O-ringed) one at a time to see if you can hear or see air (steam) vs water flow etc. The temp gun should also show you a temp differential if there is one...

The very first thing I'd do is to use a temp gun to see if the THERMOSTAT and other areas on the block - are reading the SAME as your TEMP gauge.... In fact - I'd do that before I did anything else.