Cooling system pressure not building - Weird - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-07-2007, 01:12 PM   #1
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Default Cooling system pressure not building - Weird

Got one for you guys. My cooling system on the 96 is not building any pressure. The upper hose is soft when hot and when you remove the radiator cap there is nothing.
Here is what I do know.
1) I am not using a drop of coolant.
2) Tried a brand new stant cap, same thing.
3) Temp gage is perfect never going over the first line.
4)Cracked the bleeder a few times and nothing but coolant comes out. No Air.
5) Overflow tank expands and contracts properly from cold to hot about 1/2".

Its as if the pump (its original) is not forcing enough pressure under the cap to seal up the button to close up the system.
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Old 05-07-2007, 02:25 PM   #2
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Default Re: Cooling system pressure not building - Weird

Quote:
Originally Posted by SSEBONNE4EVA
Got one for you guys. My cooling system on the 96 is not building any pressure. The upper hose is soft when hot and when you remove the radiator cap there is nothing.
Here is what I do know.
1) I am not using a drop of coolant.
2) Tried a brand new stant cap, same thing.
3) Temp gage is perfect never going over the first line.
4)Cracked the bleeder a few times and nothing but coolant comes out. No Air.
5) Overflow tank expands and contracts properly from cold to hot about 1/2".

Its as if the pump (its original) is not forcing enough pressure under the cap to seal up the button to close up the system.
When you remove the radiator cap there is nothing? I presume you mean that there is no pressure and that coolant is up to the very top of the radiator neck? If that is so, then your symptoms sound like a cap that is not functioning properly. I would pressure test the system to make sure it can hold pressure and has no leaks. If that tests OK, then I would try a new cap and a new thermostat. Temp never going over the first line could be a thermostat sticking open.

When you squeeze the top radiator hose, is it full of coolant or full of air? You should be able to feel the difference. Soft sounds like you might have a slug of air in there.
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Old 05-07-2007, 02:33 PM   #3
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I got a question for ya...when the thermostat was changed, was the o-ring type gasket installed with it?

For a while, mine would not pressurize either, but I WAS loosing coolant...slowly, but steadilly. I thought it was the waterpump gasket at first, then I replaced the cap, but it still had the same problem. Then I checked the last thing it could be...the o-rings for the coolant pipes. Sure enough, one had broken, causing the small leak. I am not sure how the S2'* are done, but it is worth checking into both these things I listed.

Other than that, I gots no other to offer
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Old 05-08-2007, 01:46 PM   #4
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Default cap

I knew you guys would bring additional thoughts. Thanks
When I said the temp gage stays under the first line I actually meant the 2nd 200 deg mark.
I changed the stat and cap last fall and re-used the o-ring grommet around the stat and installed a new gasket. Its possible it was buggered up but the temp is running perfect so there can't be any blow by happening other than the drilled stat.
Yes the upper hose is soft and when I squeeze it quick the cap hisses then seals.
I'm thinking maybe air in the system too or the upper hose is just too worn out and soft although it should blow up like a baloon but it doesn't.
When removing the cap there just isn't any pressure but the radiator is full.
Any further thoughts?
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Old 05-08-2007, 02:14 PM   #5
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(This presumes you have no coolant leaks in the system - internal or external.)

I would siphon a gallon out of the radiator into a clean jug; remove the thermostat and re-fill the cooling system using this procedure: http://www.bonnevilleclub.com/forum/...=article&k=100 That should minimize air in the system.

If after a week, the top hose is still soft when hot, or feels full of air, I would install a new cap.
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Old 05-09-2007, 10:40 AM   #6
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Default pressure

Update: I installed the original Delco radiator cap this morning and I am now holding coolant pressure.
This defies all logic. I tried a brand new stant and no pressure, and the stant that was on there worked fine for two yrs. Now I'll have to search for an alternative replacement cap as I don't want to leave the Delco on there.
Any of you guys use any other brands?
Bill, thanks for the reply, when installing the stat I used the procedure you mentioned.
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Old 05-09-2007, 10:58 AM   #7
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My only thoughts are something was on the sealing area of the radiator causing you not to seal 100%
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Old 05-09-2007, 11:16 AM   #8
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Why not get a new Delco cap? Stay with the brand that works!
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