My blazer has a new radiator and 190 stat but I keep noticing lower levels in the over flow container.Upon checking it two or three times I noticed the cap on it had been striped out so I took some plastic from a plastic bag doubled it up and replaced the cap.Now the question is will that cause the sealed coolant system to stop evaporating coolant.I am sure it is evaporation because the vehicle does not loose a drop off coolant along with any other fluids.What do you think am I rite?

 

That shouldn't cause any issues.

 

Might want to add some UV dye and do a cooling system pressure test. Lower intake manifold gaskets like to spring leaks on these things, and they can be difficult to detect without the dye.

 

Like I said no drips no leaks any were but with the cap to the over flow striped isn't that then vented to the atmosphere and in tern available for evaporation from the canister itself.Just my thought on it so i double wrapped the threads on the overflow canister with plastic from a albertsons grocery bag then screwed the cap back on gently now we will see if there is any more coolant loss due to what I can only imagine to be evaporation.

 

More likely to be leaking and boils off before it can drip on the ground. Time will tell

 

The overflow container itself technically is not a sealed unit. It still has an open drainage hose if the level inside of it were to get high enough. I would highly doubt coolant evaporation is occurring from a loose overflow cap. How recently did you replace the radiator? You might just still have some air trapped in the pressured system slowly working its way out. If not, like the Capt said, I'm suspicious of a leak somewhere. After I did my intake manifolds, I still didn't think the system was quite right. Pressure tested the system cold and found the upper radiator hose was leaking on the engine side from reusing the factory clamp. Switched it out and no problems since. I never would have found the leak looking a a hot engine...

 

Ok tried the uv dye and pressure test no head gasket leaks or failure of the factory clamp,I believe all that leave,s is the over flow cap issue and since the plastic bag seal these latest 90 degree days no antifreeze smell or fluid loss at all like normal when shutting down after a warm run in 90 degree weather. Capt,oh by the way I am at 98,000 original miles don't know if that makes any difference or not on the gaskets probably not but thought I might just mention it.And without the smell like I was experiencing after driving 10-15 miles maybe with a little luck I may have resolved it.Only time will tell at least it wasn't head gaskets I wasn't looking forward to that if it can even be done with engine in.?

 

Ok I take that back the pressure test revealed no head gasket leaks but on further inspection and a little hand wiggling of the factory clamp at the radiator top hose found the leak or should I say seepage when wiggled by hand and more than likely seepage while under pressure while engine was hot just enough to let me smell the antifreeze smell but never find a real leak other than hot under pressure seepage.Topped off the over flow took out the plastic bag doing nothing but probably not allowing fluid to return to the radiator over flow and vice a versa.

 

I looked it up on google and the overflow canister is a sealed system or so they say on google and on mine you can see were the cap meets the top of the container it has a seal to seal it before the threads.

 

2003 Blazer overflow tank is not a sealed system.

03 2003 Chevrolet Blazer Expansion Tank - Cooling System - Dorman, Replacement - PartsGeek

Here is an example of a sealed system (2006 Pontiac G6). They always say "do not open hot" on or near the cap.

http://www.partsgeek.com/catalog/200...l?brand=dorman