Cooling System Weirdness - Expansion Tank Cap?

[OK-944]

So for the past three months that I've had my 85.5 back on the road, the cooling system has been pretty consistent - drive 40 miles to work....drive back...take the 12mm and bleed a little more out of the top hose. Next morning, coolant a little low...add more coolant...and repeat - day after day but with a little less bleeding required as time moved forward. Top hose always pressured after warming up.

Now, suddenly, the top hose feels squishy after warming up....and the bottom hose does not feel warm enough - almost like coolant may not be circulating at all. And yet the engine is not overheating...in fact feels a bit cooler. Also...the coolant tank seems to overfill very easily now....and is always above the maximum mark after a long drive.

Could this be something as simple as a defective expansion tank cap...not holding pressure?

[porschetub]

Had a very similar problem,my cock- up as I had the early tank/cap swapped to the later tank/cap and it stopped puking coolant.
Its most likely your cap,it appears they fail more than most think.
I'am still kinda having issues with air also and like you it seems a little less each time like your car,but my car is running a little hotter than I would like also.
Have you tried jacking the car up in the front or bleeding off air parked on an upward slope ?.

[whalebird]

opening the bleeder when it's hot only creates air pockets. Let it cool off before opening the bleeder. Then remove the cap and fill it untill coolant comes out of the bleeder. Yes, the cap is a common problem. Most parts stores have a domestic made cap that works great in a pinch. You can use that until you order one from our host here. Elevating the front of the car is a good idea when bleeding. If problems persist, hook up a pressure tester to make sure you don't have small leaks somewhere else.

[Timmay!]

If your upper radiator hose is not stiff when the engine is hot, you're losing pressure thru a water leak or the cap. Since you're not leaking, it must be the cap.
Here's how we do it:
We always bleed the air out of the system with the engine warm. Remember that air can be trapped in the heater core as well, depending on the operation that required the bleeding.
You shouldn't need to elevate the car to bleed. Take a look at the bleeder bolt in relation to the rest of the cooling system and you'll see that it's the highest thing. (If the block doesn't have water in it, fill that first. I use a shortened upper rad hose turned upward to act as a funnel.)
Just fill the tank till you get water flowing out the 12mm (head) hollow bleeder bolt. Then, squeeze the upper radiator hose so water squirts out the bolt and while doing that, tighten the bleeder bolt down. That's a good start.
Warm the engine up and crack the bleeder bolt open. You'll usually get a little steam so be careful. Squeeze the upper radiator hose till you get water and, again, simultaneously tighten down the bleeder. I'd still take the car for a drive with the heater on, then re check for more air.

[mattdavis11]

If you put the car on an incline, wait until you get water out of the bleed screw. Tighten it down, leave the cap off and lower the nose. Watch the bubbles in the over flow. Fill to spec.