Coolant system pressure test?

[Ralph50]

96 Lesabre, 115K miles, 3.8L, Vin K.
I have been loosing some coolant, not alot but some. I intend to do a flush and replace with the green stuff. Before doing so I pressure tested the cooling system and it lost about 1/2 psi over a 10 minute period. Had it pumped up to 15 psi. I think I will repeat this test and check for leaking around the test equipment. Also considering it is cold here in Michigan and the car was cooling down while working on the car is it possible that the cooling lowered the pressure?
So, for my question, what is an acceptable pressure reading per time?

Thx

[coffey2]

For what it is worth, I have a suggestion.

I too had a minor coolant leak that and I could not find it. I finally succumbed and put in Bars Leak and over the course of 4 weeks the leak has almost stopped. From what I have read, this is not harmfui to the coolant system, although the coolant is now an ugly brown.

I had the leak, got it almost stopped and then flushed the system thinking I could rinse out the ugly Bars Leak. Well the leak returned to an unacceptable level, so I put back in Bars Leak and am leaving it in. My leak has almost stopped completely again.

Buick also sells a similar product that comes in tablet form.

[Ralph50]

Yes I have used the tablets before. They are made from fround up ginger that swell and seal the leak.

[Hapynzap]

Bar Leaks is just a band-aid on what could end up being a hemorrhage (Upper intake manifold failure)

If you are lucky you might get 5-10k more miles out of it then a quick painful engine death when it finally lets go.

[Ralph50]

I did some research on these tablets. GM actually uses these in there cars. The dealer also sells these. They were having small leaks and by what GM documentation describes as very very small leaks. GM started using there tablets and have saved alot of money.

R

[HotZ28]

My advice is to be careful with the “rat pellets” and do not use more than absolutely necessary to stop a small leak, otherwise when summer approaches, the radiator will be partially blocked and the car will overheat. Ask any radiator shop and they will tell you that a common cause of poor coolant flow and radiator efficiency is the overzealous use of rat pellets! I much prefer to use Bars Leaks liquid aluminum for small leaks and liquid copper for larger leaks. You should only use 4 oz of this product to begin with, or ½ of the 8.5 oz container. Remember, more is not necessarily better in this case!

[imidazol97]

Originally Posted by Ralph50

I did some research on these tablets. GM actually uses these in there cars. The dealer also sells these. They were having small leaks and by what GM documentation describes as very very small leaks. GM started using there tablets and have saved alot of money.

R

Actually the material which GM uses in the pellets for seal from the factory or when replacing radiators is made of ground organize material, such as walnut shells or some spice. I don't know if the Bar's Leak is made of the same...

[BNaylor]

I recall seeing info on the GM cooling system sealant tabs on a GMTechLink web site several years ago but many were shut down to people other than in the dealership. So from my memory I don't think the tabs were used by GM until 2000-2001 model years and up.

Also, the composition was herbal in nature and Ginseng rings a bell to me. Made from Ginseng root but I could be wrong.

I once pulled a radiator where off the shelf stop leak was used as a band aid fix. The lines in the aluminum part of the radiator were clogged which caused overheating at extended idling periods.

[Ralph50]

Update to the original thread.
The car is loosing about a pint a week.
Today I did another pressure test on the cooling system. This time the motor was running and hot. I wanted to see if the head gasket was blown and pushing air into the cooling system. The pressure stayed around 10psi. dropping slightly when the cooling fan turned on and also dropping about 2psi when the motor was raced. Basically it held pressure. No leaks!
I then checked the vacuum and it was at the high end of the green on the tester but still not low like I suspected.
I am now thinking maybe the radiator cap could be bad? I figured that if the cap were bad then the extra coolant would flow to the overflow bottle. I see nothing.
I will check the trans fluid again.
I hesatate to change the UIM and LIM just because this is a known problem. It may not be my problem.

[imidazol97]

Originally Posted by Ralph50

Update to the original thread.
The car is loosing about a pint a week.
Today I did another pressure test on the cooling system. This time the motor was running and hot. I wanted to see if the head gasket was blown and pushing air into the cooling system. The pressure stayed around 10psi. dropping slightly when the cooling fan turned on and also dropping about 2psi when the motor was raced. Basically it held pressure. No leaks!
I then checked the vacuum and it was at the high end of the green on the tester but still not low like I suspected.
I am now thinking maybe the radiator cap could be bad? I figured that if the cap were bad then the extra coolant would flow to the overflow bottle. I see nothing.
I will check the trans fluid again.
I hesatate to change the UIM and LIM just because this is a known problem. It may not be my problem.

A heated motor should bring the pressure up to 15, 17, 18 pounds, whatever the cap is rated at. A lower temperature means the coolant can boil and burp into the reservoir tank.

What happened when you turned off the motor and let the pressure sit? Pump it up to 18 and wait with the motor hot.

I'd be sure I had a good cap on the system.

[Ralph50]

Yes I did this. The motor was hot enough for the rad cooling fans to turn on. When the car was turned off I lost maybe 1/2psi over 10 minutes.
Here are some facts noticed; 1-with the motor running and at about 12psi when the cooling fans came on the psi dropped to about 8psi, I waited and just before the fan turned on again the psi climbed back up. That tells me that the coolant temp change affects the static psi. So when I turn the car off and watch the psi gauge the 1/2 psi drop could be the coolant in the rad dropping. 2-when I raced the motor the colling psi would drop then climb back up when back to idle.
I will change the cap but a bad cap just allows the coolant to go into the bottle not disappear.
Still confused.

[Ralph50]

Update on this problem. Took off the UIM and there was puddles of antifreeze. Even though I pressure tested it was still leaking. I also replaced the LIM, 37 dollars for the gaskets. I started the engine and the lifters were ticking loudly. More than just one. They ticked for about 2-3 minutes then got silent. I hope they were loud cause of the antifreeze getting in there. But there was no antifreeze in the LIM only upper and the oil is clean so I dont know about the ticking. Job took 8 hours. cleaned the throttle body because it was caked with carbon, cleaned the EGR cause of a fault code 1460, it was sticking and used that PB blaster, its a big job, lots of disconnected wires, vacuum lines off, replaced the plastic elbow on the LIM, alternator was off, had to clean the idle control pintel in the throttle body, I hope the lifter noise is gone.

[jbjslambert]

i had same problem, sounds identical even down to the lifter ticking. check my post with UIM PICS and you will see the puddles in the LIM like yours,joe

[BNaylor]

Originally Posted by Ralph50

I hope the lifter noise is gone.

The best thing to do is run about 8 ounces of Seafoam engine treatment directly into the crankcase for a few hours. The Seafoam will help remove any residual water/coolant which will cause the lifters to tick. Then drain the old oil. Install a new quality oil filter and add new oil.

This has worked for many of us that had UIM and LIM issues that experienced the ticking sound after the job was completed.