86TpiTransAm

Ok, I've got a dual problem here on my '91 Firebird (3.1 V6) and I'm trying to figure out what the heck is going on. Problem 1 .... car is losing antifreeze (see my other post). Problem #2 ..... the overflow tank is full but when the radiator gets low on antifreeze the fluid in the overflow tank doesn't get sucked in to the radiator to help out.

My question I guess is ..... isn't the fluid from the overflow tank supposed to get sucked in to the radiator if it gets low? I know that the tank is there so if the engine overheats for whatever reason the fluid gets pushed into the overflow tank but I also know from my '86 that the fluid is supposed to get sucked in from the tank if the radiator gets low. Or at least that's what it does on my '86.

One thing that's confusing me is that the tube from the overflow tank to the radiator goes right to the neck of the radiator and it "appears" that it's actually above the hole that the radiator cap seals when you put it on it. If that is the case, how in the heck would the fluid get sucked in to the radiator from the overflow tank if the hose is ABOVE the opening which is sealed by the cap??

Am I missing something here ... maybe the whole concept of the overflow tank? Someone PLEASE clue me in on this.

Any help, advice, suggestions, or otherwise would be greatly appreciated.

coolram62

iTrader: (2)

Before manufactures started using overflow tanks the coolant was just vented to the ground.What happens is the radiator cap internal seal/spring assembly lifts when the cap's pressure limit is reached but instead of venting to the ground it's captured in the overflow tank.When the radiator/motor cools down the inner seal lifts and vaccuum pulls the coolant back into the radiator.If you're having problems with the overflow tank you could have either a faulty radiator cap(which can cause other cooling issues)and/or the hose from the radiator to the tank could be dried out or collapsed.
Hope this maybe of help to you.

Gramps

iTrader: (1)

i think that the problem is that those rad caps dont work unless there is water pressure pushing on them. a 14lb rad cap will blow off with coolant at a certian temp, but if the rad is low, air pressure builds instead of fluid pressure (air pressure isnt as much as fluid because air can be easily compressed where as oil and water cannot). so not enough pressure is opening that valve to create a vacuum. if you find your leak then itll be fine, but rarely does that coolant line kink, plug, or even warm up for that matter.

Reid Fleming

iTrader: (2)

Does your temp gauge work fine for say half an hour and then suddenly rocket towards the red zone? Is your coolant overflow tank bubbling like a witch's cauldron?

I hate to say this, but it sounds like a blown head gasket. I was stumped myself on this. Coolant would suck itself into the overflow and then not come back to the radiator. No fluid on the ground, oil looked great. Pressure test showed no leaks.

I stopped in at a radiator shop and they looked at the bubbling coolant overflow tank (my fans come on at 190 and 200F). The car wouldn't get hotter than 200 sitting there.... They put an emissions probe into my overflow tank and found I was getting 850 hydrocarbons in there.

86TpiTransAm

No my guage doesn't make any erratic jumps. It just gradually warms up like usual and then gradual gets closer and closer to 220. When the radiator first gets low enough, the temp guage gets up to about 220 but doesn't go over that mark. That's the point when I know the radiator is low and top it off and go about another 100 miles or so and do it all over again.

I don't get any bubbling or gurgling in the overflow tank.

I know the problem is very odd. I suppose it still could be a blown head gasket but it doesn't show any of the typical signs of a blown head gasket. And if that's the case then it could be a bad water pump even though it doesn't show any of the typical signs of a bad water pump. Or a cracked heater core even though it doesn't show any of the typical signs of a cracked heater core.

See what I'm getting at here?? I hate guessing. Always ends up costing more money that way in the longrun.

Thanks for the suggestions guys. If you have anymore suggestions, advice, comments, etc please post them.

BADMAN

iTrader: (13)

When you start your car after it has been sitting overnight does white smoke(steam) come from the tailpipes and then dissapate? A small leak in a head gasket will do this. As the engine cools water can seep into cylinders and then is burned upon startup. Also check dipstick for brownish color(water in oil).Badman

86TpiTransAm

No white smoke from the tailpipes and no sign of water in the oil. Basically I've checked all of the normal reasons why the coolant would be disappearing.

No sign of antifreeze in the oil.
No leaks visible under the car.
No leaking into the passenger floor to indicate a cracked heater core.
No signs of antifreeze going through the exhaust.
No signs of antifreeze leaking into the transmission through the in-radiator tranny cooler.

I did fix the problem with the antifreeze not being sucked out of the overflow tank however. I pulled the radiator cap off my beretta and put it on the firebird and that seemed to fix that problem. I just bought that new radiator cap that was on there about 3 weeks ago so I guess I just got a bad cap out of the box.

Now if I can just figure out the coolant leak problem I'll be set. One possibility that I haven't checked yet is the possibility of a leak near the top of the radiator on the front side and it's evaporating off the radiator as it runs down before it gets a chance to leak onto the ground.

I'll keep posted if I figure anything new out and if anyone has any other suggestions, please let me know.

TIA!