My car runs perfect and never overheats but for some reason whenever I hot rod around and then shut it down it overflows the overflow tank.
I've changed the stat, coolant, blead the system and check the fluid level daily. There is no oil in the coolant and no coolant in the oil.
Anyone have a clue as to why it is suddenly doing this, is there some valve, hose or bypass that could be clogged?

 

In your case i think Its basically purging it self of excess coolant in the over flow tank. As long as you have coolant in the actual radiator I wouldnt too much worry about it. When it overflows do you put more water back into it?. If you are then you need to stop b/c its getting rid of the water it doesnt need. Keep an eye on you5r coolant levels via the radiator cap and make sure you have coolant in there.

 

Yes I check the fluid level both in the radiator and in the overflow tank. Usually it doesn't recover all that it purges and this over time results in some spilling out. I usually try to make sure that the overflow is at the correct cold or hot level (as appropriate) and that the radiator is full an blead. The main point is, is that it never use to do this so I'm wondering what has changed that I'm not seeing.

 

I had that happen to me last fall before I put my car away for the winter, I was just driving around one day, and I could smell antifreeze inside my car, I pulled over and it was freaking throwing up out the overflow tank,

well I checked everything, and I thought for SURE I had a blown gasket
but I just let the car cool way down, checked the Radiator level, filled it up, added alittle more to the overflow tank, and now it sits RIGHT where it's supposed to, hasn't changed AT ALL since........I bet you just somehow added too much, I didn't realize it, but I did....or is it possible there is a huge air bubble in your radiator??

 

Try a new radiator cap. Make sure it is 18 psi like it is supposed to be.

 

Forgot to list that I did that too, and changed the fluid and have tried different ratios of coolant to water, but thanks for replying.

Is it possible to have a very small headgasket leak or a very small crack in the head (besides the one in the head on my sholders) that does not exhibit any other signs or problems?

I'm wondering if the end tank seals in my 10 year old radiator (which is clean inside) might be leaking slightly at temperature and allowing my coolant to boil and purge. I do have some residue signs (white powderish) around my tanks but no sign of liquid leak. Could this be a sign of steam leaks when at temperature and under the added pressure of higher RPM opperation? I'm grasping at straws but I can't think of anything left to do but pull the radiator and have it checked out and replace the end tank gaskets if required.

 

You could always rent/buy a pressure tester to check the cooling system.

 

Good idea, see if I can find anything static, only problem is if it is a hot only problem then I'm going to have to put the wet suit on and work quick

Thanks

 

Is it using water if you don't refill it? mine blew a head gasket and had similar symptoms. If it is a bad gasket it will keep blowing coolant out the overflow until there's none left in the motor. My car would seem perfectly fine for 40 minutes of driving then suddenly blow the lid off the overflow tank and start running hot. If I checked it every 10 minutes or so while running the overflow tank level would be slowly rising more than the normal hot-cold marking distance.