07 CTS-V with an LS2 engine. OEM thermostat is 186*F. Dexcool 50/50. Cruise temps were 192 consistently while car was moving while at least street speeds. Stopped at a light quickly had temps rise. Water pump was replaced under warranty in December.

Installed a 180* thermostat from Lingenfelter, but it's nothing more special than the one that sells in Summit. I think it was made by Motorad. Refilled system with 50/50 Dexcool, ran engine with burp tank cap off, filled tank as the level dropped until it stabilized, capped it, drove it, let it cool, then ran with cap off to help it burp, topped off, etc. Fans were adjusted to come on at slightly lower temps than OEM.

My first question: Is there a high flow LS2 style thermostat out there? The OEM stat may offer greater flow than the readily available aftermarket thermostats out there, not sure.

Second question: Coolant temps are obviously slower to rise to cruising temps, sometimes cruises at 188*, but sometimes it creeps to 194 and stays there for a while. It appears the temps come down with engine rpms above 2000, but cruising around in 6th results in rpms below 2000 (no need to read a "drive it over 2000" comment). Stopped at a light has the temp stop at 195 and go no further, but the fan adjustment is the reason for that.

We are a bit frustrated because we thought cruising temps would be a little lower. I understand the systems cooling capacity has much to do with the temps, so we weren't expecting 180* cruising temps from just a thermostat change. However, I think cruising temps above 190 indicate to me either there is still air in the system or the aftermarket thermostat doesn't flow well. I've been told the LS2 cooling system is a bugger to burp, but I've done what I think is a thorough job ensuring there's no air in the system. Perhaps I missed something.

People who installed 160* thermostats in this engine have reported cruising temps in the 175* range. I felt a 160* thermostat was a little much on the cool side.

Hoping for some good technical input.

 

You can try drilling the tstat so that there's a constant flow of coolant even when it's closed, but that's not gonna do much. Also, there are no 'high flow' tstats out there...they are what they are.

Also, I don't see a problem with cruising temps in the 190*s, so what' the need for a higher flowing tstat? Yes you can get the 160*, but that is a little cold for max engine efficiency.

You engine runs better at operating temp, so there's no need to go lower unless you live in the south or have FI on there. If your engine is knocking at operating temps and you need to lower the engine temps just to kill the knock, then you have a bigger problem and you need a better tune. A stock or close to stock engine does not need lower engine temps, as they were designed with a certain operating range in mind and that's where they perform best. Stick with the 180* and have the fans come on stronger, but I would not worry if you have a max of 195* coolant temp. That's normal and going down to say 180* is not going to do squat for you or extend the life of your engine.

 

My point was that the cruising coolant temps increased with the lower temp thermostat compared to the OEM thermostat, hence the concern about flow or actual opening temp.

 

It's all about the fans and how strong and when they come on. You could get a 160* tstat in there, but if you don't adjust the fans accordingly then you're not gonna be any cooler than stock.

So unless you change the fan settings, that 180* tstat is going to keep the coolant temp the same as the stock 186*. The reason why cruising temps went up were not because of the new tstat, it could have been a warmer/more humid day and that's what caused the temps to go up 3*. The coincidence was that you changed the tstat then, but it had nothing to do with it. A colder tstat will not make the temps go up, but at the same time it will not make them go down without fan settings change.

Now if your temps would be over 210* with the new tstat I would be worried about lack of flow as you say, but going from 192* to 195* is not a big deal and it's most likely because of an ambient temperature change rather than the tstat. Maybe the coolant is low, maybe there's an airbubble in the system, maybe the cap is not on right...there could be lots of things to attribute a 3* change in temps other than the tstat.

If you're worried about the opening of the new tstat, take it out and put it in a pot of water and start boiling it. Keep a thermometer in the water and watch as the temps go up and see when the tstat actually opens. That's a good way to test the operation of a tstat and see if it actually opens at the temp it was designed for.

 

I've tested them in that manner before, dunno why I didn't this time.

Fans are a moot issue because they were adjusted for the new stat, but the temps are low enough not to have them in the equation. Outside air temps were consistent enough that they were not a factor.

I have read that LS2s are real buggers to bleed out all the air pockets. Is there a specific procedure to follow to ensure all the air is out of the system?

 

let it idle with rad. cap off for couple min, fill w/dexcool and water till it seems liek its topped off then hold down the throttle to bout 1,500rpm for bout 15sec then check again do it twice then cap it
thats wat i do
but everyone awlays got a diff way of doing this

 

Interesting...know it's probably been discussed a few times, but this is a recent thread. Subscribing. My 06 Z51 Vette stays around 200-205 in traffic, even though it's about 40-50 degrees out. I bought a 160 t-stat and am waiting on Mike to get down here to tune it. It just seems my car should be a lot cooler. My turbo 6.0 LQ9 GTO ran 180 at the most.