I have an 86 that I did a radiator flush on a few weeks back. I refilled with coolant, ran until the tank opened at 195 degrees, then burped until it stopped filling (about 3gal). Drove it home and got it up to temp to try and pack it, came back from vacation this week and found a big puddle of coolant that ran out of the overflow tank. Overflow tank and radiator are still full near to the brim and coolant gauge is still reading LO, which means the temp gauge is still reading an air bubble and I need to pack about 1gal more of coolant. Any advice?

 

When I had my C4 a old timer shop Forman when I brought my car in the shop gave me this advise to me.

I know lot of people going to tell you different advice and not to it, but I owned my C4 for 24 years and 5 years serviced my coolant this way, will not clogged system.

I use take match book, take match stick out, and cut a very small piece to stick in the thermostat which leaves it open and install and service and run the engine.

That small open it letting coolant do it thing, and when it gets hot enough and opens that cardboard match stick leaves, and you should now have properly serviced system.

That small piece of the match book never hurt the system. It worked for me!

Here is my car I had to show you not blowing smoke?

 

It took me a long time as a total noob to cars and mechanics to figure this one out. So you are not alone my friend.

First things first, for proper functioning of the cooling system, you need to ensure you do not have any vacuum and pressure leaks. I mean, your cooling system needs to be sealed entirely.

When your system heads up, the fluid has a bit of an expansion. And right after refilling, there are small pockets of gas that seriously expand with heat. When the pressure of the expansion exceeds 16psi (what does your rad cap say?) it overpowers the cap spring, and then flows into the "overflow" container The white, usually dirty, rusty, muddy coloured tank in your passenger side front headlight cavity.

Now, when you turn the car off, the fluid cools, and contracts.

As it contracts, it sucks, 'vacuums' the fluid back up the same hose from the overflow container up to the rad.

Technically speaking, as long as your overflow tank is full, and your system if filled up via the rad cap, while waiting for the tstat induced fluid level to drop, then you fill the sytem to the brim and put the rad cap back on......that is all you need to do, sounds like this is what you did, and over the next few driving cycles AS LONG AS YOU ENSURE THE OVERFLOW TANK IS FULL OF FLUID AND THERE ARE NO LEAKS then as the gas escapes out the rad cap, it bubbles out the overflow tank, then, when the system cools, it will vacuum from the overflow tank and draw it back into the engine to fill the void age left behind as the gas escaped.

You can absolutely get fancy, and go about various other ways to release that gas, but the system is designed to take care of it.

I could never figure out why so many owners (me included) cam on the forum saying they could not purge their systems.

90% of the time it is because the "suck back" ability is hamstrung by a breach in the system. In other words, if there is a perforation in the seal (intake manifold base is the usual suspect, at either cyl 7, or, 8) then the vacuum will suck in air.....not the fluid from the overflow. And then you end up on this never ending cycle of "low coolant" light coming on....and the overflow tank always filling up on you but never being sucked back.

If that doesn't make sense feel free to ask questions for clarity.

Also, you could just have a leak somewhere as the source of your puddle. Which.....eventually creates the scenario i've just written about.

 

Sounds good, appreciate the write up. The only thing that concerned me was, before the flush with the key turned, the temp gauge read ambient coolant temp immediately at around 100 degrees. Whereas now, it reads as LO until the car has a chance to heat up, which makes me think it's reading the ambient air temp because it hasn't been packed fully.

I was fiddling with the overflow tank while doing the flush, so I suppose I'll double check all the seals there and just run it some more.

 

be sure not to let it overheat, and be sure that ur system is sealed, with fluid in the overflow. If the system has gas in it still, it should purge it out, and suck back fluid in its place.

You want to get it hot so it expands but not so hot u overheat. 👍