![]() When that happens the local temps run away. With 50/50 or straight water even with high system pressure your never that far from locally boiling the coolant from these hot spots. What you are using is the higher natural boiling point of waterless to keep these extreme hot spots wet and surrendering heat to the coolant. These hot spots are exhaust seats and spark plug bosses. The point here is to suppress localized boiling around the traditional hot spots that have temperatures considerably higher than the bulk coolant temp the gauge is reading. Then figure with 50/50 and a 20 pound cap the boiling point is like 265 so if you were running 220 with 50/50 this is only a 45 degree cushion. Your numbers look what is expected with waterless, at 240 your under the waterless boiling point of 375 by 135 degrees and that at just atmospheric pressure which would be a with zero pressure cap. At the very least, I would install an oil temp gauge. If take away the water from the coolant and let it get hotter, you risk superheating the oil, or at least giving yourself a need to control oil temps to prevent blowing past those tolerance thresholds. piston-bore clearance, bearing spaces, ring gaps, oil temps and viscosity, etc are all tailored to hit their target "sizes" when the oil and coolant reach a stasis around 200 degrees. It was fine, but one of the things that you have to realize is that everything about an engine is designed to operate at (you guessed it) a temperature based on boiling point of a 50/50 coolant. The reason we want to keep temperatures low is because of the limitations of the boiling point of water-based coolants. As long as the coolant can transfer enough heat, the actual temperature isn't a big deal. You will superheat one spot while the rest isn't, and you can get a cracked or warped pan ![]() What happens when a vehicle overheats is more like using an acetylene torch on one focused spot in the pan. Imagine having a cast iron pan in a 500 degree oven. If you remove the boiling fear, a piece of cast iron that melts at 2200 degrees doesn't care if the gauge reads 195 or 295. It's not the temperature of the water that causes damage, its that when it boils it creates pockets of steam which can no longer absorb heat like liquid water can, and the combustion chambers get super-heated. Think of it this way: Every minute you have thousands of ignition events of 2700 degrees. The only reason we have to keep it cool is because once the water in traditional coolant boils, it's all over. The actual temperature of the coolant is pretty irrelevant. One particular day I left Phoenix towing that trailer headed for Flagstaff which is 150 miles of "up." Coolant hit what I'm guessing was 300 (280-degree gauge) and it never did a thing. I ran Evans in a Caddy 500 for years towing heavy stuff - probably around 10,000 lbs. Here is what they do to the 500 Cadillacs. You might try pointing an infrared heat gun at your heads in different places to check for hotter areas, and also compare exhaust header temps. I just say that as an example to demonstrate that the heads are usually where the problem originates and often finding your solution there will correct the problem. The idea was to NOT drill the coolant holes in the mid cylinders, which may allow the coolant to return before it gets to the back.but to make it easier to flow at the back and then return past the mid cylinders. Not sure if air is being trapped or just insufficient coolant, but it works. This allows more flow at the back which subsequently flows forward. One of the solutions they came up with is to drill a couple additional coolant holes in the deck of the block at the rear. There are lots of people who have temp problems on the Cads. Then you also might back the timing off a degree or two and see what the result is. ![]() Some radiators are modified to be multi-pass which helps. There are lots of people running large engines.some with superchargers and they cool just fine.so it has to be doable. I would see if adding a couple fittings and a temporary purge doesn't alleviate the problem. The heads on an engine are the primary source of heat, and the block usually is not problematic. Many other engines can trap air too but no one really wants to talk about it.everyone assumes its the radiator. LS engines have vents to let trapped air purge. Are you sure you don't have air trapped in the heads.
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