I'd like to add something here. Installing a 160° stat will do nothing for lowering temps UNLESS you tune your fans to come on at a lower temp than OEM. A thermostat controls your lowest temps. A 160° stat ensures the car will never run under 160° once its thoroughly warmed up. Your cooling system is responsible for the high end of the temp range. I do agree with the post above that on a totally stock car, there's not really any reason to run cooler than the engineers intended. Running cooler can, however, fool the pcm into thinking the car hasn't warmed up completely, so it may slightly richen the fuel/air mixture, which sometimes makes a small increase in power, because the stock tune is really lean, for emissions purposes. On a built/modded engine, cooler temps can help control spark knock, so then a cooler temperature would be desirable. I have a 25° UD ASP balancer. Now that I drive in Florida half the year, I think a 10% UD would be as much as I'd ever recommend, that or standard OEM size. If you truly want a cooler running engine, and actually need it to run cooler, a larger, aftermarket radiator is the answer. My .02

 

Regardless of any of this, it's all governed by physics, and in this case by Fouriers's Law. The majority of the cooling effect is by heat transfer. Heat is transferred by contact from the coolant to the rad fins, and then from the fins to the air in contact with the fins, assuming the air is cooler than the fins. So, unless cooler air is moving across the fins, the air in contact with the fins just heats up, and there is little cooling effect. The whole system depends on air flow. No air flow = almost no cooling. And I did state that the 180 stat would be of little use if stuck in traffic, because there's not enough air flow until the fan comes on. And by stuck in traffic, I don't mean 45 or 50 mph on a highway where you could legally go 70. I mean stop and go, and with extended stops. I've got the OEM 186 stat, but also a DeWitts rad. Even on a hot day, if I'm 40 or above, temps are under control. The rad fan doesn't come on. In fact, I'm about 12F over the stat set point when poking along at 45. At 50 mph and over, I'm like 194 to 196 consistently, unless I'm throttle off on a long decline, where I've actually seen temps drop to 187. I've also seen 221 - 223 on a hot day stopped in traffic with the same setup.

It all comes down to the fact that the system must be able to transfer at least as much heat as is being generated, or the temps go up. In your case, if you can transfer more heat going at 45 than is being generated, then temps will drop to an equilibrium point governed by the rate of heat transfer. The 160 stat should be wide open I'd say around 170, so the fact that you see 180 at 45 mph is not surprising, but it wasn't what I was getting at. Again, don't expect a lower set point tstat to help for more than a couple of minutes if you are stuck in stop and go traffic, unless the fan has been programmed to ramp up sooner. Also, the fact that you have a built engine doesn't imply that it's producing much more heat under normal driving. The heat generated is directly related to how much gasoline you're burning. Without changing anything else, burning more gas means less efficient use of the fuel, going faster or accelerating harder, or maintaining constant speed on an incline, or any combination of these.

 

So I did this procedure I found from another message board for a C5 Z06:

Start w/ a cold engine
Remove rad. cap
Idle for 1 minute
Install cap
Cycle RPM from idle to 3000 until coolant reaches 210F
Shut off engine
Remove cap
Start engine
Idle for 1 minute
Install cap
Cycle RPM from idle to 3000 until coolant reaches 210F
Shut off engine
Remove cap
Top off

I got some coolant running out from the overflow hose when I opened the cap at 210 the first time, it looks like I had over filled it with the vacuum device. It was definitely acting like it was releasing trapped air, with the level going up and down. After the level stopped changing, I actually had to add a little to get it back up to the fill line.

Then I drove the car and nothing changed.

Next I attached a vacuum source to the expansion tank return (upper) line as suggested. I disconnected the return hose from the tank and adapted the venturi tube that came with the fill kit to the end of it so it pulled from the hose. I connected a hose to the venturi outlet into a container and connected the air inlet to the air compressor. I did see a little foamy coolant going into the container. I let it go for a couple of minutes. I guess some air came out, but it's hard to tell since the exhaust shop air comes out of this port on the venturi too.

Drove it again and still not right. Maybe the temps are slightly lower, but still in the 205-210 range at 1500 RPM.

Any other ideas? Did I let the venturi vacuum on the line go long enough? Think I'm going to do something other than work on the car for a while...

Thanks!

 

I'd be damned awful careful removing the coolant tank cap with coolant temps of 210°F!!!!! It can be done, but it's not on my list of safe things to do!! You are inviting scalding hot coolant to a party nobody else will attend but you......

 

100-105 here in DFW and i'm sitting at about 185-190F AC on and idling.

 

does anyone run a fan over ride kit, to run the fan all the time in stoplight traffic ? I've been thinking about doing it.

 

Any other ideas to get the trapped air out of the cooling system? I did both techniques from my earlier post again, and the temperature is still behaving the same way. I may go to work where there's a larger air compressor so I can run the venturi tube vacuum on the surge tank return hose for longer.

 

The "old fashioned" way worked perfectly for me after I installed the reworked heads on my 427 short block. The filler cap is taken off and you jack the car up about 6" on the same side as the filler cap (obviously the left front). The air "bubble" will always go to the high point of the cooling system........then begin filling the "space" that WAS the air bubble, and voila, you should be golden. In my instance I poured in another gallon after the air bubble was taken care of. Works like a charm!

 

You need 190-220*F coolant temps in modern engines to minimize wear/tear and improve efficiency/economy

never run an engine long at sub 185*F especially modern units

They must rapidly warm up including oil temperature (mainly oil temperature matters most)

There are boat applications where people desire cold 140-160*F coolant temps (of course it is favorable to power), but when they build the engine there is still a need to rapidly warm the oil temps up (cold water, HOT oil) and in doing so they build the engine with excess piston-wall clearance to make up for the cold water. DO not attempt this with a typical engine without consulting somebody who knows what they are doing.