Mystery coolant problem

mynd66September 1, 2008

I have a 99 Olds Cut. 3.1L chevy V6. It had a lower intake manifold leak. I took everything apart and replaced the seals, replaced the water pump, replaced the thermostat, changed the oil... put everything back. Then I filled it with coolant, drove it for a little bit, put more coolant, blead the system till pure coolant came out of the bleeder... Then drove the car over 50 miles. Temp gauge was still good until I pulled in my driveway and shut it off it all boiled right out of the resivior cap. This also happened prior to me changing the seals and I thought that changing the seals would do the trick.

I'm not sure if the cap is bad, it was changed not too long ago but this is the third or fourth time this happend. I'm not sure if its the radiator or maybe the heads. Maybe I didn't bleed the system as good as I should have. I'm not a mechanic but I took the time to read the manual and get some help from a mechanic. I cannot figure out whats causing this to happen. I have used the search and didn't really pull up anything to really help me solve the problem.

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I suspect that the system was not full, possibly air space in the heads. I don't know about the location of an air-bleed on the 3.1 L V6, but I think is is similar to the 2.8 L V6. My 2.8 l V6 did not have an air bleed. the drill was to fill it as much as possible with a top most hose removed and when coolant started flowing out the hose bib, re-attach the hose and fill as much as possible.

Pre-mix the antifreeze and water, usually half and half (unless you purchased the pre-mixed stuff). Be on your toes when you purchase antifreeze. The 100% antifreeze and premix often occupy the same shelf space and it easy to get these mixed up. Use this mix to add coolant to the system. Do not try to mix in the radiator since it is too difficult to get the desired mix ratio.

Fill the overflow bottle with coolant to a level above the full mark.

With the heater control set to high heat, radiator cap off, start the engine. Add coolant as the level sinks (for short period of time) and then put on the radiator cap. Don't remove this cap again during the filling process.

Don't run the engine no more than 5 minutes because there is probably air in the heads. Stop the engine and allow to cool. You should see coolant being drawn out of the overflow bottle.

Check the level in the bottle and start the engine. Allow it to run long enough to open the thermostat. The upper radiator hose has a significant rise in temperature when the thermostat opens.

Stop the engine and allow to cool. As the coolant cools, it will suck more fluid from the bottls, that is, if the fill cap is in good condition and there are no air leaks in the line running from under the cap to the overflow bottle. You can hasten the first two cooling periods by running some water over the radiator core.

Check the fluid level in the bottle. Always add coolant to the bottle, never at the radiator cap. The cap must remain in place to keep from admiting new air into the system.

After these first 2 minor thermal cycles, there should be enough coolant in the system to run the car for a short time. Drive the car until the thermostat opens and the temperature comes to near normal. Park it and allow to cool. Resupply the overflow bottle and after this 3rd thermal cycle, there should be enough fluid in the system to drive the car at mild service conditions. Watch the coolant level in the bottle for the next 2 to 3 cool downs, add coolant as needed, and when the level stabalizes, you may go back to the normal check schedue.

Because the intake manifold was disturbed, keep an eye on the oil level and condition over the next few days. We're looking for possible coolant leaks into the crankcase. On this engine, the intake manifold sits between the heads, acts as the valley cover, and has coolant passages. A rise of oil level and color change may indicate coolant leak into the crankcase. Oil contaminated with ethylene glycol will have a brownish color and may...

    Bookmark   September 2, 2008 at 2:34AM
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Thanks for the reply. I had a bad radiator cap so I changed it. Its a 15 psi cap. I hope that does the trick. I will fill and bleed the system as you said. I checked the oil and it seemed a bit higher than when I checked it after I changed it yesterday. But I checked it today after a drive so the engine was a hot and may have caused the oil to expand. I'm just hoping the problem is not the head gasket. I'm no mechanic and changing the seals on the upper and lower intake was pretty challenging. I know going beyond that to change the heads is going to be quite a job. Thanks again --Ray

    Bookmark   September 2, 2008 at 8:56PM
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A bad radiator cap could certainly cause the system to not fill on cool down. In one case, instead of sucking coolant out of the overflow bottle and into the radiator/engine, it took in air. In another case, if the cap did not hold pressure, it allowed the coolant to boil at a lower temperature.

Air can be admitted if there is a leak in the hose that runs to the overflow bottle.

    Bookmark   September 7, 2008 at 3:47AM
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Mr. Dandy, is there a danger to adding straight 100% coolant to the reservoir? Is straight antifreeze just as corrosive as straight H2O?

    Bookmark   September 19, 2008 at 9:22AM
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RE: Posted by sailor86 (My Page) on Fri, Sep 19, 08 at 9:22

"Mr. Dandy, is there a danger to adding straight 100% coolant to the reservoir? Is straight antifreeze just as corrosive as straight H2O?"

I don't know of any danger, but, its not necessary unless the existing coolant mix in the engine was less than 50% antifreeze. The minimun freeze point occurs at about 50/50 (or so) mix of water and ethylene-glycol. The exact low point may be given on the antifreeze container. Increasing the amount of antifreeze beyond this point raises the freezing point.

I keep a mix of 50/50 water/antifreeze in the garage to use for makeup. You can also buy a pre-diluted mix - just don't make the mistake of later forgetting that it is already diluted and dilute it again.

Both water and antifreeze are corrosive, but according to auto manufacturers, the most corrosive effect is admitting air (oxygen) to the coolant system. Once the fill cap is put in place after a fill, it should stay in place and all makeup liquid be added to the overflow bottle. Once the system has 'burped' the air out of itself over several heat and cool cycles, in theory, very little new air should enter the system. It is the oxygen, combining with other metals and fluids, that creates sludge and corrosion products of the metal parts including the engine walls.

After changing the coolant, I recommend adding a can of water pump lub and anti-corrosion. Add the lub/anti-corrosion first before refilling the system. (It can be added any time before the system is full, but putting it in first, you are assured of having enough space for it.- Been there; Done that; Ran out of space)

    Bookmark   September 21, 2008 at 2:26AM
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