Question about 1996 GMC Suburban

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Radiator loses water overflow tank full. replaced cap and no signs of leakage

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  • Michael Masters
    Michael Masters Jul 13, 2010

    When traveling or during a morning start; Do you notice any white smoke coming out the tail pipe?



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No obvious leaks, ehh? First of all, start the truck, and watch the tailpipe. Do you have any smoke which is by chance white, and smells sweet? Now, turn it off real fast. Let it cool. Get a volunteer, take the cap off, put your hand over radiator fill neck. Do you feel pressure against your hand? Check the oil. Does it look kinda' milky? Does the radiator water look bubbly? Finally, when you pour water in, does it go down rather quickly, but not a leak (Within 2 minutes)? These may indicate a broken head gasket. Otherwise, start looking around for cracked old hose, cracked hose necks, loose clamps, etc.

Posted on Jul 13, 2010


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The overflow need to be filled with water?

Yes, it is important to include the overflow tank or bottle as integral with the radiator and coolant system as a whole. They all intermix. Actually, the level in the overflow tank is a true measure of the correct amount to keep your coolant at. There are two marks on the overflow: full hot and full cold. The coolant system on all modern cars is a sealed system and therefore should never require adding, save a very small amount through evaporation within the overflow tank- the only part that is open to atmosphere.

So once you get all the air out of the system that is possible, both in the engine and in the radiator, you have a full level everywhere, including the overflow tank where it should always remain somewhere between the full hot and full cold marks.

You are right that the overflow collects the heated radiator coolant. But it is due to the expansive properties of coolant-or water- that it expands when heated, (but not boiling-that is very bad news of a different sort). Your radiator cap is designed to open at a specific pressure, just enough to allow coolant to flow into the overflow. As the engine and coolant cools, it contracts, the level drops in the radiator, and a natural vacuum there will siphon the overflow tank back into the radiator until it is full again. That is why you have the full hot and full cold marks.
I will shut off the lecture now. I hope you have liked my answer. If not, I give you permission to kill me now- if I may so jest.

Mar 06, 2015 | 1992 Toyota Corolla

4 Answers

What is causing antifreeze to come out overflow tank?

Could be a defective radiator cap, or a leaking head gasket.

Oct 28, 2014 | 1999 GMC Suburban

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Losing water causing overheating

My first question is make model and year.
Second, are you saying the engine is boiling over into the overflow tank and onto the ground ? Is the tank about half full when the engine is cold ?
Have you run the engine with the thermostat removed to test ?
Usually when you can hear the coolant moving around, you have air in the system and it is not full of liquid coolant.

Feb 04, 2013 | Cars & Trucks

1 Answer

My 2000 chrysler voyager radiator fluid bubbles in radiator overflow tank evn when cold nd when turning over. I just had head gasket replaced whats going on

I suspect a crack in the head or block. The cooling system is suppose to be closed so any air has to be coming from somewhere - if the head gasket is good then the air is likely to be coming from a crack. A pressure test will confirm if your system is not air tight. That is if you are seeing bubbles in the radiator water if you just mean you are losing water through the overflow then it might just be the radiator cap needs replacing as it is not sealing the system when it gets hot.

Jan 23, 2013 | 2000 Chrysler Grand Voyager

1 Answer

Car loses water from overflow cap. Replaced water pump, thermostat and overflow bottle and cap.

Stop me if this has NOTHING to do with your problem (or if it's already been solved)...I don't know a lot about cars so...My Ford Taurus kept overflowing antifreeze from the reservoir cap. Car started to over heat and kept spilling"/dumping" antifreeze every time I turned the car off. The antifreeze reservoir had been replaced less than a year prior, and water pump, radiator, etc looked at. I got a free estimate that stated my water pump was NOT the issue, but I did need a new radiator and my reservoir tank needed to be replaced (again)....$800 parts and labor.... However...I noticed the overflow holes on the tank, and also that the orange liquid (antifreeze), was also spilled around the cap lid. I also noticed the CAP on the antifreeze reservoir would loosen when tightened completely- hence, not sealing correctly. So I went to the dealer, bought a new reservoir cap for $15, replaced it, and never had an issue after! I also found out that the CAP was a DEALER PART ONLY, and when the tank itself was replaced, the CAP was the OLD one! Problem fixed! Maybe it's similar? Or something "more serious".

Mar 28, 2012 | Saturn SW Cars & Trucks

1 Answer

I changed our my rediator and now the sensor light saying radiator coolant is low and the buzzer won't stop going off. The radiator coolant level is fine and my temp gauge is fine. Any help would be...

Do you have an overflow tank that has low level in it?
LEVEL CHECK The coolant level should be checked regularly. Serious engine damage can occur if the engine overheats. CAUTION
Check the coolant level when the engine is cold; serious injury could result from escaping steam or hot fluid if checked when hot. If your car is equipped with an electric cooling fan, make sure that the ignition switch is OFF. The cooling fan will automatically operate if the ignition switch is on and the engine coolant temperature is high, or if the wiring connector on the thermostat housing is disconnected.
  1. Depress the button on the thermal expansion tank (coolant recovery reservoir) safety cap, if there is one. Allow all of the pressure trapped in the system to escape. CAUTION
    The radiator is not factory-equipped with a safety cap. Do not remove the radiator cap before removing the expansion tank cap, or when the engine is hot. Fig. 1: Remove insects and debris from the radiator fins 85811096.gif

  2. Remove the expansion tank cap. The expansion tank should be 1⁄3 full, unless Full and Low marks are provided. The level should be well above the bottom of the tank when the engine is cold.
  3. If it is not, carefully remove the cap from the radiator. The radiator should be full.
  4. Add a 50/50 solution of ethylene glycol (or other suitable coolant) and clean water. If there was no coolant in the expansion tank, fill the radiator until the level is near the inlet port and install the radiator cap. Then, fill the expansion tank to the specified level, and secure the expansion tank cap. When checking the coolant level, the pressure cap should be examined for signs of age or deterioration. Check it for a worn or cracked gasket. If the cap doesn't seal properly, fluid will be lost and the engine will overheat. A worn cap should be replaced with a new one. The fan belt and other drive belts should be inspected and adjusted to the proper tension. (Please refer to the belt inspection and adjusting procedures, earlier in this section.) Remove the radiator cap and run the tip of your finger around the inside of the filler neck. Check for excessive deposits of rust or scale around the filler neck lip and the filler port. Make sure the coolant is free of oil. Replace the coolant as necessary. Hose clamps should be tightened, and soft or cracked hoses replaced. Damp spots, or accumulations of rust or dye near hoses, the water pump or other areas indicate possible leakage, which must be corrected before filling the system with fresh coolant. Periodically clean any debris, leaves, paper, insects, etc. from the radiator fins. Pick the large pieces off by hand. The smaller pieces can be washed away with water pressure from a hose. Carefully straighten any bent radiator fins with a pair of needle nose pliers. Be careful as the fins are very soft. Don't wiggle the fins back and forth too much. Straighten them once and try not to move them again.
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Jul 05, 2010 | 1985 Mazda RX-7

1 Answer

Losing water from radiator cap have tried replaceing but problem still there is there diferent caps or is the fault with radiator local garage says no

You should not be losing water from your radiator cap. When the water in your system reaches such a pressure that it needs relief, it will normally flow into the overflow tank (the opposite occurs when the system is cold; water flows from the overflow tank into the radiator).
So, the first thing I would do is to get the proper cap for your radiator.
Second, I would check to make sure my cooling fan was running (I'm assuming that you lose water when the engine is hot).
Third, I would make sure to bleed the system if I had to add a significant amount of water (bleeder should be on top of the fitting that your top hose goes to; loosen and observe until water flows cleanly without bubbles, then close).
I have to think that your cap, new or not, is the problem.
Hope this helps you.

Nov 15, 2009 | 1998 Honda Accord

1 Answer

Cooling system over flow system. and how it works

The overflow system has a different radiator cap than on yesteryears cars. The old cap would let extra water vent out of the radiator and you would lose that coolant. The newer radiator cap lets water go both ways through the vent tube. Then the overflow uses a tank to catch and return the water. It siphons the fluid back into the radiator.

The system was invented when the thermostats were set at 205degrees and up for pollution systems. It also saved some aluminum with smaller radiators and using a plastic overflow bottle instead of a bigger metal radiator.

Oct 22, 2009 | 2000 Ford Taurus

3 Answers

Coolant coming out of the overflow spout after shutting down.

about 100K miles? sounds like a blown head gasket is allowing coolant to be pushed out the exaust,and combustion pressure is pushing fluid out the overflow.have your compression tested.

Sep 21, 2009 | 2000 Chrysler Town & Country

2 Answers

'97 subaru overheating

head gasket most likely.

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