The Mystery of the Missing Coolant: come weigh in!

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My wife's 2003 Hyundai Santa Fe (2.7L) seems to be losing coolant. When I was changing the oil last weekend, I noticed that the reservoir was just about empty, so I filled it to the full line. I took it to a mechanic who pressure tested the system as well as the radiator cap. He said everything checked out fine and he couldn't see any leaks. We drove it for a couple of days and the level got toward the Low line. I filled it to the full line. A couple of additional days, and the level is sitting halfway between low and full. I filled it back to the Full line last night. Basically, I've added probably a couple of quarts over the last week. I can't see it going anywhere. I do not believe that it is going into the oil, because when I changed the oil (at around 7000 miles on Pennzoil Platinum) the oil looked fine. It wasn't the least bit milky or anything to indicate a coolant leak. For now, I'm stumped. The mechanic said if it kept losing coolant to bring it back and he would do a dye test. I'm just curious if anyone out there has had a similar issue--especially with the same engine--and might have some insight. I'm going to continue to drive it, watch the coolant level, and check the engine oil. The car runs/drives fine. All comments are welcome! PS. I've been checking the levels with the engine cold. I've been consistent on that.
 
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mrdctaylor

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If it were that, would it be leaking outside or into the oil? I've seen no evidence of either. Also, would the system still pass a pressure test?
 
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Small coolant losses are usually a bad radiator cap. In new cars, it's also the reservoir cap.... These are reasonably cheap, and easy to change. If not that, then it's probably a leaking water pump. With the engine off, look for wet spots or see if the shaft wiggles... Bad head gasket would leave chocolate foam in the coolant reservoir...
 
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I wouldn't put anything in it yet.If it passed a pressure test you should be good but I would do another.Also check the coolant tank hoses they are often like vacuum hoses and the connections get loose over time.Does it have a radiator cap also you could just check it there.
 
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Reservoir tank leaking? If the tank is outside the pressurized portion of the system, it could leak and not be detected by the pressure test.
 

mrdctaylor

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Originally Posted By: javacontour
Reservoir tank leaking? If the tank is outside the pressurized portion of the system, it could leak and not be detected by the pressure test.
Hmm. Now that is an interesting theory. I'll look more closely at that.
 
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Don't put sealant in a radiator, you will clog the cooling system up. Major repairs.... No chocolate foam, no head gasket leak. Change the reservoir cap as a first step...
 
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mrdctaylor

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Nope, no chocolate foam. Everything looks clean. I drain/fill the radiator myself every 30K miles or so and have done this since I got the car with 30K miles on it. I really take care of it and I don't plan to add any sealers to it.
 

Astro14

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I've seen HG leaks that go only into the cylinders. No chocolate foam, it's not going into the oil and it passes the pressure test, but the HG is still bad. If you've got one or two really clean spark plugs, you know it's going onto those cylinders. If you're losing coolant, you've got a leak. It's just a case of figuring out where.
 
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You've received some good advice so far, and some not so good. Adding anything to a cooling system, like a "car-repair-in-a-bottle" is a really bad idea, especially at this point. It is way too early to add any crud to your cooling system. Adding that stuff should be a desperate, last chance, Hail Mary pass, kind of a deal. Diagnose the problem correctly first. Coolant that is going "missing" is typically not that hard to diagnose. Any good, experienced mechanic, in a good shop, will be able to figure it out. Dyes and all that are unnecessary in virtually every case. The idea that a leaking head gasket always leaks into the oil is just flat out wrong. I cannot count the number of bad head gaskets I've replaced over the years and I'd say 25% or less had coolant in the oil, if that. It is entirely possible that coolant is leaking into a combustion chamber and being burned and it is not enough to be seen out of the tailpipe, yet. It may be that having someone follow you, who knows what to look for, on the highway, will be helpful. Pressure testing doesn't have to only be done with the engine off. Sometimes to find a leak it helps to have the engine running while adding pressure to the system with the pressure tester. Don't exceed the maximum pressure, though. Pressure testing should be done with both the engine cold and at operating temperature. Hot engine parts expand, cold parts contract and that movement may be part of what's happening. Looking at the spark plugs will tell you a lot. Cylinders burning coolant usually have plugs that are cleaner looking or the insulators may have a slight color cast similar to the color of the coolant. Either way they will look different than the others. Other good possibilities are a leaking side tank or a hose. Gently wiggling hoses and such while under pressure may reveal the leak. It may be the heater core that is leaking. The box that houses the heater core may be wet or dripping coolant. Typically you can smell the coolant, or the windshield may fog up, when the heater core is bad, but not always right away. It may take a week or two for symptoms to be noticeable. You can do a lot of diagnosis yourself with a good inspection mirror, a bright, light source, some time spent looking around thoroughly and some patience. Drive the vehicle for a bit to get the coolant hot and the cooling system pressurized and have at it. Check all around the water pump area, top, bottom and sides of every coolant hose, the radiator tubes and tanks both front side and back side, all around the engine top, bottom and sides, and then check it all again. Engine hot, engine cold. Finally, cooling systems may "use" a little bit of coolant over time. Particularly an older vehicle. There doesn't have to be any kind calamity for that to happen. Wait another week and see if any more coolant needs to be added before doing anything else. Is the side tank part of the pressurized cooling system or not ?
 
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Originally Posted By: javacontour
Reservoir tank leaking? If the tank is outside the pressurized portion of the system, it could leak and not be detected by the pressure test.
IMHO, this is the most likely culprit. Either a cracked tank or hose leading to the tank. Both are common problems. It is unlikely that it is a head gasket leaking into the combustion chamber. A leak like this goes the other way because the combustion chamber is operating at a MUCH higher pressure than the 14 or so lbs of pressure in the cooling system. When your mechanic pressure tested the cooling system, he would have seen this on his gauge when the engine was running.
 
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Originally Posted By: KB2008X
You've received some good advice so far, and some not so good.
OK then. Try all that stuff above. Do a UOA. Take it to a mechanic and spend 1000s diagnosing a $2500 car. Then pour in the Blue Devil.
 
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Originally Posted By: turtlevette
Originally Posted By: KB2008X
You've received some good advice so far, and some not so good.
OK then. Try all that stuff above. Do a UOA. Take it to a mechanic and spend 1000s diagnosing a $2500 car. Then pour in the Blue Devil.
It may very well need Blue Devil, or something like it, but not before the actual problem is found and understood. If your tires were a few psi low would you fill them with some kind of tire sealant crud before you figured out why they were low ?
 
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Originally Posted By: KB2008X
It may very well need Blue Devil, or something like it, but not before the actual problem is found and understood. If your tires were a few psi low would you fill them with some kind of tire sealant crud before you figured out why they were low ?
Some of us have more experience and can jump to the answer. If it was something simple like a cap, reservoir, or hose don't you think the mechanic would have found it? Some do prefill their tires with an sealant. It could save someone's wife or daughter from being stranded in a bad spot. High quality sealant is not "crud". GM put "crud" in as the factory fill.
 
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