Coolant level lower when hot?

Is the coolant level supposed to be slightly lower when the engine is hot? This goes against how I understand it to work. Here's the synopsis of events: Replaced water pump, thermostat & flushed and replaced coolant (using Ahsai's method) about three weeks ago as PM. Used a vacuum filler but I know I got some air sucked into it Drove ~200 miles with the burp valve open & added some additional coolant as necessary. Closed valve. All fine for a few weeks Top hose on expansion tank started spitting coolant out under pressure. Replaced the hose clamp & replaced what little coolant was lost Took some drives to get the coolant up to temp and make sure the repair worked Now when I check the level cold, the coolant is just below the max line. When I check it hot after shutting down & system pressurized (valve closed), it's just above the min line I'd also replaced the tank about 4 months ago. No sign of intermix. I'm not too worried about that.

Sounds almost completely normal. I think you still have an air pocket to work out. Open bleeder valve and leave it open. Do at least 5 complete heat/cold cycles. Check coolant level.

Mine acts completely opposite than that. Min line when cold, Max line when hot. I agree that it seems like you may still have a little air in the system. As long as you don't see any leaks, and it's not overheating I don't think there's anything to worry about - just leave the burp valve open and keep an eye on the coolant level... fill as needed.

I just went through this same scenario, you have air in the system. Once all the air is out you should read lower when cold and higher when hot.

Yeah I agree, you may have some air in the system. May need to jack up the rear end pretty high and let it run to get the bubbles out now. I guess another question, when the car cools down, does it return to the same level or remain low?

I think you're all right about the air in the system. After I replaced that clamp on the expansion tank I drove it around in hot weather for over 50 miles and got the temperature up to 108 C. No issues with coolant escaping that hose so I thought I was good. Yesterday I drove it to go jogging & drove it around a little again to get the temperature up. Put it in the garage and all looked good. After I posted this, I went back out into the garage last night and discovered it had spit out some more coolant after I shut it down and the level was quite a bit below the min mark this time. Any idea if it can suck air into the system via a loose expansion tank hose and cause air bubbles? I just topped it up and will take it for another drive at lunch. Hopefully I can catch it spitting out coolant and tighten down that hose until it stops. I need to get this solved. I have my first HPDE event this weekend. Although it only seems to do it when it's shut down and the pressure builds, I know coolant on the track is a very bad thing.

Update - I caught it leaking coolant from the connection to the bottom hose of the expansion tank under pressure. I thought the tank was moving a little too much and remembered I couldn't get one of the bracket bolts very tight when I replaced the tank 4 months ago. So, I siphoned out the tank and removed it. Found the loose bolt in the bracket was gone. I got a new bolt and hose clamp & replaced both. I was able to get the bracket tight this time (had a new 10 MM deep socket that I didn't have last time). I got the tank re-installed and re-filled that night. I've kept the burp valve open for 6 hot/cold cycles and except for the first drive after refilling the tank, the level hasn't dropped anymore. My next few drives will be with the valve closed and the tank under pressure. I'll see what happens.

Just remember the burp valve closes when cool and opens/rises when hot. Sounds like you are good to go. Good job!

After removing and re-installing the cooling tank and replacing the lower hose clamp, I took it through 6 cycles with the burp valve open & 3 cycles with it closed. Looks good. No coolant dripping or spraying out of any of the hoses and the level hasn't moved a single millimeter. I'm pretty happy I was actually able to remove the coolant tank & get the car back in running condition in a single evening and still get to bed on time. After siphoning out the tank, my next coolant buying decision may be based on taste.

Next time use the coolant drain plug to lower the level below the tank! Antifreeze is deadly. You can control the flow with your finger and simply pop the drain plug back in.

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I considered that but didn't want to drain 2.5 gallons. I knew from recent experience that siphoning the tank would only take a couple of minutes. Not something I'd want to do on a regular basis if I did this for a living. I had a glass of water handy to rinse out my mouth just in case. I think as long as you don't swallow any and rinse quickly the risk is very low.