What's everyone using for a radiator cap rating?
The old system/eng used a 15 psi IIRC, but these LS engines, at least in the 4th gens i think used a 18psi cap. Later models are up to 19-20 i think. Not overheating, but the temp runs around 200-210 ish. Just curious if anyone upped to a higher rated cap. Am using a too low rating?. I still have a 15 psi cap. The only "stock" part in my cooling system is the heater core. Which makes me wonder if it could even handle the pressure from a higher rating cap...anyone.

 

I used the original factory cap on my LS swap with no issues except when my plastic side tanks cracked. By chance I had a tube of JB weld and it got me home. I now have a cheapo eBay aluminum rad, didn’t bother to check the pressure. Works great, 160 cruising temps on a cool day.

 

What thermostat you using?
I have the stock 189 degree and it's built into the stat housing. I've thought of switching, but I don't wanna go lower than 170. I don't think I can pull the stat off the housing, so I'd have to swap both.

 

I'd stay with 16 PSI radiator cap. It raises the boiling temp of coolant and also is a high pressure limiter for the cooling system. I don't think it interferes with operation of the thermostat which is temperature based. And the system needs a way to expand and contract. The radiator cap is the expansion valve, and the overflow tank is the expansion reservoir.

My understanding is LS engines are easier to cool than the old SBC. I don't have any cooling problems with my 427 and I'm using all stock parts except an upgraded radiator. Engine has a stock thermostat too.

 

Whats your running temp? Im just not used to seeing the temp gauge hover around the 200-210 range even at 5am driving to work.

 

It usually stabilizes around 195°F. I think it goes to about 205°F after a hard pull. Wouldn't surprise me if it peaks higher but that would only be temporary, not sustained. Temps in that range help the oil reach ideal operating temp faster. It's a good thing.

I don't have air conditioning or a trans cooler, I'm sure that would drive it higher.

 

Choose thermostat to get engine at a proper operating temp on the street. If you race then the thermostat is going to be wide open anyway and make no difference. The only people that think about low-temp thermostats are drag racers because they start the race before the engine is fully warmed and the race is done in a few seconds.

For reference, I've had my thermostat in hot water on kitchen stove and it was open around 195°F and cracked open before that.

 

I have a 160 t stat. I have no overflow/expansion tank. Never overflowed. In stop and go traffic on a warm day I’ll get hot…220+ but that’s because I have junk eBay fans
I will usually be 90 degrees above ambient temp.

 

That's a little hard for me to believe. The stock coolant reservoir is huge for a reason. I think maybe there's something you're not telling us, or you've already lost coolant to the point it won't lose any more.

The radiator cap actually has two valves. One is high pressure relief valve, the other is a vacuum valve for system draw down. Without an expansion tank you have no reserve volume of coolant for the draw down so your radiator is sucking in air every time you drive. All that air in the system makes the cooling system less efficient and can accelerate corrosion.

 

Just to clarify, that is with CTS sensor placed in the front location of driver side cylinder head. It would read higher temp if placed in rear location of passenger side head which is stock location for LS engines.

 

Well ive got AC and an auxiliary trans cooler. So maybe that has an affect on the temps then. Guess ill leave well enough alone. Maybe i need to take a look at the gauge/sender. My sender is on the pass head too.

 

Your numbers seem fine to me, and probably equivalent to mine considering the temp offset with passenger side CTS location. Maybe keep an eye on it in the heat of summer.

The numbers I stated are from the engine ECM, not a gauge. My gauges are stock and only good for eyeing if it's generally about right, or below normal, or above normal.

 

The main difference on a hot day is the cooling fan runs more frequently, almost too frequent it seems at times, but no overheating...yet.

 

I've never paid much attention but I'd guess both my fans run continuously in summer because they're programmed to not shut off until 185°F. Honestly, it's healthier for the fan motors to stay on then to cycle on/off all the time.

I suppose I could shut off one or both at highway speed but it sounds like a lot of work to do all the data logging to figure out the criteria for that because it's going to change with MPH and IAT.

 

I had the overflow tank installed for several months in the summer, but left it empty. It never got any coolant in it after several months, so I just pulled it out. This may not be the case for others but it’s what happened on my car.
When cold my coolant level in the rad is about 1 inch below overflowing.

 

You didn't see any fluid because the pickup tube didn't start out being submerged. Your radiator was still sucking air during draw down. It was identical to not having a reservoir at all.

The draw down function is what starts the process, and it doesn't work unless the pick up tube is always submerged. This is why the minimum fill level in the coolant reservoir is so high. If you had submerged the tube then you would have seen fluid exchange with the radiator.

 

Fluid level in my radiator is all the way up to the cap, basically right at overflowing. Yours would do the same if you had a reservoir. Basically mine purged as much as possible and yours cannot.

You've had a good streak of luck that you did not lose more. I would not keep pressing that luck....