Coolant expansion tank question (car running hot)

[The Mad Hatter]

OK, i was here months ago with overheating issues, but after replacing several parts, everything was great.  The gauge stayed halfway between the light and the "cold" area.  Even at worst, it only got up to the light.  Well, a few weeks ago, my upper rad hose split close to the engine.  I cut out the bad section and reattached it, and everything was ok again.  I finally get around to replacing the hose, and now, the gauge will not come below the light, and is holding consistant ABOVE the light, but not to the point the fan comes on.  The only thing i changed was the upper rad hose, and refilled it with 50/50 coolant.  

Now, my question is, when i got home, i could hear a hiss/gurgle coming from the expansion tank.  Its coming from the cap.  I don't remember it ever doing that before.  I'm thinking the cap seal has failed?  If its not getting up to pressure, that would cause it to run hotter, correct?  It's NOT leaking any coolant, as the tank is full to the max line.  I'm going to replace the cap today (as i need this car back on the road), but looking for any opinions on this.  Thanks in advance!

[jtanguay]

you have an air lock in the system... how did you fill it???

[The Mad Hatter]

Poured it in the tank, like i've always done.  I squeezed the rad hoses to get any lingering air bubbles out.

[jtanguay]

you should fill the rad, then the tank.  

now you need to run the car with the expansion tank cap off and let it get up to temperature so the thermostat opens.  some guys drill a small hole in the t-stat to help bleed out the air, and i've seen vanagons with coolant hoses that had small bleed valves (very cool!).

so let it idle there up to temp for a good 3-4 mins and verify that the whole rad is getting hot/warm.  (good time to make sure that the fan comes on too)

the level in the tank should rise considerably, but mine never overflowed...  i did however rev it a bit to help it get up to temp.

[The Mad Hatter]

OK, i let it do just that, and it is running cooler now.  Mine looked like it would overflow, so i shut it down.  But, it is running cooler now.  Not as cool as before, so i probably need to do it again.  Thanks for the help!

How do you fill the rad?  There isnt a cap on the rad like on my Chevy's.  The only opening in the system is the expansion tank.

[jtanguay]

OK, i let it do just that, and it is running cooler now.  Mine looked like it would overflow, so i shut it down.  But, it is running cooler now.  Not as cool as before, so i probably need to do it again.  Thanks for the help!

How do you fill the rad?  There isnt a cap on the rad like on my Chevy's.  The only opening in the system is the expansion tank.

you need to disconnect the upper rad hose from the head and fill from there. of course you dont want to put too much, so it doesn't leak back out when you reconnect it.

did you check the t-stat to make sure its working right??  seeing as how difficult it is to get at (with power steering) it is almost worth it to just replace when changing the coolant.  or at least make sure its opening right on the stove with some hot water.

[The Mad Hatter]

The T-stat is practically new, i just replaced it a few months ago.  I verified it was working before it went in.  The car didn't start running hotter until after i changed the hose and refilled the coolant, so i know it had something to do with that.  And my car doesn't have PS.  Getting to the T-stat is pretty easy (if not messy).

[jtanguay]

The T-stat is practically new, i just replaced it a few months ago.  I verified it was working before it went in.  The car didn't start running hotter until after i changed the hose and refilled the coolant, so i know it had something to do with that.  And my car doesn't have PS.  Getting to the T-stat is pretty easy (if not messy).

yea... aside from having to drain the coolant it isnt so bad.  some shops actually suck the coolant out with a machine... lucky buggers!!!  :lol:

did you remember to flush the system with a chemical flush, like prestone heavy duty flush? it's a very good idea... if you didn't no biggie if the heat works great, but it is definitely recommended on an older car.

[Possum79]

So many people say to use a chemical flush. I don't really agree with that. If your system was always maintained then go ahead but other wise you could start to wash away things that are keeping leaks from happening.

I blew a freeze plug on a blazer from using a prestone flush system. The freeze plug was not fun to change.

just a slight warning that it could cause problems.

[burn_your_money]

 If its not getting up to pressure, that would cause it to run hotter, correct?  

I don't think so. It will run at the same temperature, however the boiling point of the coolant will be lower, so it will actually boil over, and then you will overheat because you are low on coolant

I don't beleive in chemical flushes. They can easily cause leaks.

[fatmobile]

How's the coolant flow into the resevoir?
 Steady or does it spurt?

[The Mad Hatter]

The coolant flow is steady.  I let her run without the cap on, got a couple of big bubbles out.  It is running cooler now, but not back to normal.  Gonna do it again tomorrow, as i wasn't able to finish since i was in the work parking lot.  Thanks for the help!

[jtanguay]

 If its not getting up to pressure, that would cause it to run hotter, correct?  

I don't think so. It will run at the same temperature, however the boiling point of the coolant will be lower, so it will actually boil over, and then you will overheat because you are low on coolant

I don't beleive in chemical flushes. They can easily cause leaks.

how does the chemical flush cause leaks?  if you have any coolant leaks you should use the old swedish mechanic trick and just add mustard powder... works really good!  :lol:  the mustard forms a really hard crust when explosed to air, but stays suspended in the coolant until then.  i suppose this could be really bad if you had coolant leaking into a cylinder though...

[Possum79]

I was told that chemical flushes are kinda like a weak form of acid. Its supposed to clean all the junk and rust away. If you have weakness in metal somewhere it can eat through it. I would assume its worse if you dont fully get it all out.

thats just what I was told and after I used it my stuff started to leak.

[Dakotakid]

Swedish mustard powder  :roll: . Ya...and these are the people who put their cars' motors in backwards....right?

It is all those months of darkness .