Can't purge coolant, radiator slowly overflows even when thermostat is closed.

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Jun 3, 2012
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Location
Bremerton, WA
1996 Jeep Grand Cherokee 5.2L V8 (Magnum 318) Stock everything.

I have a gurgle in the heater core on startup, I didn't use to so something changed.

Bleeding proceedure:

RADIATOR CAP = OFF
HEATER SET = HIGH
BLOWER FAN = HIGH

Let idle at varying speeds until engine reaches 195F and the thermostat opens.

The problem:

Even from a cold start the radiator level will slowly rise and start pouring out the radiator fill neck at a rate of ~4fl. oz. per minute. Attempting to bleed the coolant system results in a net loss of coolant in the system even after the thermostat has cycled several times.

I did the exhaust gas in coolant test with the blue reactive fluid and it passed. Is the next step buying a leak down tester?
 
Some vehicles take something like 3000 rpm to bleed air properly. The coolant overflow is probably just from thermal expansion of the cold coolant. Don't let the car warm up too much with the cap off. Try to rev the engine with the coolant still cold, or cool. If that fails, make sure that if there is a small bleeder hose running into the reservoir, that it is open and CONSTANTLY flowing coolant, hot or cold.

Other than that, try to run it normally, getting the revs up.

Most cars that I've seen recently have a high point hose that serves that purpose, just to keep air always being directed to the reservoir. They can become plugged with sludge or bits of rubber, sometimes even the steel fittings will corrode inside, reducing the flow to almost nothing. If you find one, and it is plugged, do not blow the debris back into the engine. Remove the fitting and clean it out off of the car, otherwise your problem will return soon.
 
Get a vacuum bleeder or you'll never get all the trapped air out.

[Linked Image from tooltopia.com]
 
Without symptoms like overheating or no heat, no need to do anything drastic yet. Before starting for the first trip every day, when the engine is completely cold check the radiator. If its not full to the top, fill it up. Then put the cap on, start up and drive. Do this several days. If you find coolant keeps moving to the expansion tank and not returning it could be a bad head gasket or a problem with the radiator cap or the hose between the radiator and the tank.
 
FWIW those "block" testers are completely useless IME.

Have you tested your cap?
 
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In addition to the other good ideas given, consider driving it for a week and determine if you are using or loosing any coolant .
 
The Lisle type funnels work great and knockoffs can be had for about $20.
In order to use the vacuum bleeder, you need compressed shop air, which might not be available to us shade tree types.
 
Originally Posted by Imp4
The Lisle type funnels work great and knockoffs can be had for about $20.
In order to use the vacuum bleeder, you need compressed shop air, which might not be available to us shade tree types.


Just how do those funnel things get trapped air pockets out?
 
Originally Posted by mattd
FWIW those "block" testers are completely useless IME.

Have you tested your cap?


I have to disagree with that. I used one on an engine with a very minor crack in the head next to the intake valve and it turned the fluid yellow in seconds.
The fluid does react quickly to hydrocarbons, granted it will not detect a internal leak into the oil or an external one but that does not render the tool "useless".
I think of it as just another testing tool in the arsenal.
 
I went out and bought the lisle spill free funnel and gave it another go.

The level kept rising in the funnel up until it almost started overflowing and then the thermostat opened and the engine took a big gulp and sucked back about 2 quarts. I never actually saw any air bubbles, but once the engine sucked back that coolant the level never rose again. I put the radiator cap back on, we'll see how it goes.

Makes sense that this method would work better because if not for the funnel holding all that fluid, my old method would have puked all that coolant into my drain container.

Still, however, after my 3 or so bleed attempts I have not added any coolant haha. Only net losses.

Radiator cap is new and tested, expansion reservoir hose has been checked for blockages, system holds 18lbs of pressure, no overheating issues and I have good but not stellar heat.
 
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Originally Posted by atikovi
Get a vacuum bleeder or you'll never get all the trapped air out.

[Linked Image from tooltopia.com]


That tool is worth its weight in gold.
 
Originally Posted by Trav
Originally Posted by mattd
FWIW those "block" testers are completely useless IME.

Have you tested your cap?


I have to disagree with that. I used one on an engine with a very minor crack in the head next to the intake valve and it turned the fluid yellow in seconds.
The fluid does react quickly to hydrocarbons, granted it will not detect a internal leak into the oil or an external one but that does not render the tool "useless".
I think of it as just another testing tool in the arsenal.


I have had several engines with badly blown head gaskets and it has never changed color. I can probably say it worked on 1 vehicle that coolant was boiling out of the reservoir. I find the best tool for this is a 5 gas analyzer. Heck I have even stuck the tester near a tail pipe of a running car (for testing purposes) and was reluctant to change color. Again, just my experience with this particular tool.
 
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Originally Posted by atikovi
Originally Posted by Imp4
The Lisle type funnels work great and knockoffs can be had for about $20.
In order to use the vacuum bleeder, you need compressed shop air, which might not be available to us shade tree types.


Just how do those funnel things get trapped air pockets out?

Hey, thanks for the snide comment...

Upon reflection, I guess it's the exact same way as a vacuum bleeder does when you're like me and you don't have a compressor. And the answer there is that neither works in those circumstances.

Put another way, the Lisle funnel doesn't get trapped air pockets out and a vacuum bleeder with no compressor doesn't get trapped air pockets out either.

Now, a shade tree type like me is never going to buy a compressor, so a Lisle funnel, while a flawed solution in the circumstances you describe, is much better in the preponderance of situations than the multiple thermal cycle method and much faster too.

And it's only $22....

Cheers!!!
cheers3.gif
 
If you just fill through the radiator with the system assembled, you can end up with some pretty large air pockets in some systems. What you are getting is typical of that.

I prefer to remove the thermostat and fill through the intake manifold until the system is full up to that level. Then reinstall the thermostat and top the system off through the radiator. Almost zero purging this way.
 
Originally Posted by mk378
Without symptoms like overheating or no heat, no need to do anything drastic yet. Before starting for the first trip every day, when the engine is completely cold check the radiator. If its not full to the top, fill it up. Then put the cap on, start up and drive. Do this several days.


This is how I get the air out in my cars.
 
Originally Posted by atikovi
HAHA! $22 for something that doesn't fix your problem is a bargain.
banana2.gif


Hmm, that's odd because it does fix my problems.
While the OP may be experiencing a trapped air pocket, my comment was pointed to a more general approach to a coolant change. I've had great success with a Lisle funnel in many applications and others have too. It works wonders in many situations but not all.

I also know, just like you do, that if a user doesn't have compressed air, then a vacuum type tool makes for an excellent door stop and nothing more. So in that case you'd be spending more than $100 for something that doesn't fix your problem, but you already knew that too.

Cheers!!!
cheers3.gif
 
Originally Posted by mattd
FWIW those "block" testers are completely useless IME.

Have you tested your cap?

I have used them at work and they are an asset.
 
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