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Discussion Starter · #1 ·
Low coolant light will come on not long after I crank up the truck. When I push the trip it goes away. I have checked the coolant level and it will look low when the truck is at running temp. When I open the coolant cap the coolant bubbles back in the tank to the normal level. Should I add more coolant or is something else causing the coolant to bubble back when the pressure is released from the system.
 

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Discussion Starter · #2 ·
Anyone?
 

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I'm not a Tech, but read this several hours ago, and no one has answered yet.

As the coolant system heats up, coolant level should never drop in your expansion tank, as long as your coolant system is "gas free". With a "gas free" system, as the coolant heats up and expands, there is no where for the expanding coolant to go but your expansion tank, in which level should rise about one inch, and develope normal system pressure. If you have gas in your system, the gas bubbles collapes under pressure and expansion tank won't rise as expected, and system pressure will not build as required. As the heated coolant system cools after shutdown, the contracting fluid decreases system pressure, and could go to a vacuum. The expansion tank cap has both a pressure relief, which lifts if pressure increases about 15 PSI. This same cap also has a vacuum relief, which is necessary to break vacuum developed when the system cools, and this is suppoosed to allow any gas in system to go back to expansion tank, which allows coolant to replace this vent gas.

If you are only getting bubbles when cap is removed, I'd suspect the vacuum relief in your expansion tank may be faulty. If you remove the cap, wash it, you should be able to suck air through the cap. It takes a slight amount of vacuum before you'll suck air through it. If you can't suck air through it, I'd replace the cap, which cost about $8. Now watch your level over the next several cool-downs, and fill as necessary. Some that had gas in system needed to add 1-2 qts to system until de-gassed. The system should de-gas itself when cooling down with a working cap.

Does the upper radiator hose get hard when coolant temp reaches 190 Deg F? If not, you probably have gas in your coolant system. Another sign of gas in system is if your upper radiator hose collaspes after cooldown. There has been great discussion in the LLY section the past few months, so you could do a search to read more.

What's the proper expansion tank level? Most say the seam 1/2 way up tank, where the "Full Cold" arrow is. Others say to fill when cold, to the plastic tab about 1 1/2 inches above the mid-way seam. I ended up filling to the tab above the "Full Cold" words. With less gas in tank above fluid, system pressure should build quicker as fluid expands during heat-up, toward 15 PSI. I have yet to blow out any coolant, with my level here, so I don't think it's too high.

If you have continuous bubbles in your expansion tank with motor running, most seem to think the likely cause is a bad head gasket. I'm not a Mechanic, so if you have this issue, be sure to confirm it with a qualified Mechanic. I wouldn't want to mis-lead you.
Again, I wish qualified others would have answered, but none have yet. These are a couple of sugjestions till you here from others.
 

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When its cold, just make sure it filled up to about or a little above the seam on the bottle
 

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Discussion Starter · #5 ·
When it is cold in the mornings, it will look low. When I go to take the cap off to put more coolant in, the coolant will bubble back into the tank to the full mark. My question is should I add more coolant, so when it gets to running temp. it will be at the right level?
 

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Discussion Starter · #7 ·
It fills it back up to the cold full line.
 

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It would seem to me, if hdroadkingc can consistantly cause level to increase back to normal by opening the expansion tank cap, that he has gas in his system, which is compressed under pressure. Removing cap depressurizes system, allowing gas to expand, which pushes coolant back into reservoir.
Am I off base?

I forgot to mention the coolant system has a vent, (bolt), which is located on top, front of thermostat housing, (located between alternator and A/C Compressor). This can be carefully loosened, with the system not under pressure, to vent trapped gas out.
 

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Sounds to me like head gaskets on a 6.5. The cooling system should not have pressure in it after sitting overnight and cooling off. When it's hot release the pressure and run it some more, if pressure builds up then your getting gas's from somewhere.
 

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Like Modified was talking about, when the truck is cool, take out the bleed bolt on top of the thermostat housing with the overflow bottle cap off, once coolant flows out of the bleed, put the bolt back in. Then overfill the coolant bottle about 1" over the cold level and see what it does.
 

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What's the proper expansion tank level? Most say the seam 1/2 way up tank, where the "Full Cold" arrow is. Others say to fill when cold, to the plastic tab about 1 1/2 inches above the mid-way seam. I ended up filling to the tab above the "Full Cold" words. With less gas in tank above fluid, system pressure should build quicker as fluid expands during heat-up, toward 15 PSI. I have yet to blow out any coolant, with my level here, so I don't think it's too high.

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I filled mine up to the tab above cold fill back when i did my block heater change in mid dec(which modified helped me with, thanks) I watched it and after a while noticed i was just below the tab. didnt think nothin of it, assumed maybe it took just a touch more for the system to be full... Marked it none the less. Checked it again this morning, as im heading to canada for some snowmobling on tues, and noticed im down more yet from my original mark. 1/4-5/16" maybe...
Im not overly concerned yet, because when i made the mark i cant remember how i was parked flat or not or if i was hot/cold...
Im debating whether to refill to original line, or just leave it and see what it looks like when i come back from Canada. hmmmmm
 
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