Coolant disappearing just about instantly - no leaks - 2010 VW Passat

I have a 2010 VW Passat with 106K miles, recently the low coolant light came on. I checked the coolant and the reservoir was empty, I filled it up and drove home but within a few minutes the low coolant indicator came back on. I drove home, about ten minute drive and the car was running hotter than normal but only cold air was coming out of the heater. I have driven a few days and two or three times it will begin to overheat, other times it will not but the heater is intermittent, sometimes hot, sometime cold, and often alternating on a given drive. The furthest I have drive is 5 miles or like 12 minutes. Only once did the engine temp really start to climb.

Today, I finally had a chance to check it out during daylight. I filled the reservoir, started the car and immediately went to check the reservoir, it was empty in a matter of seconds. I could find no leaks or even drips anywhere. I spent a good ten minutes looking around.

I checked the oil and it looked normal, nothing milky.

Where is my coolant going? Any ideas. Thanks.

If you find your car has suddenly developed a voracious appetite for coolant, and you cannot figure out where it’s all going, you may well be looking at a blown heater core. Sadly, if the leak is hard to find, the reason may be that the coolant has been leaking into your cabin when the system is cold, and instead of making fog it’s creating a puddle. The first place I usually check to confirm a bad heater core is the passenger-side floor. If it is soaking wet, and so are any forgotten shoes or fast-food bags lying around down there, then I know to suspect the heater core.

If there is no evidence of any leaks, heater core or otherwise, it is pretty likely to be the head gasket. There is a breach between the coolant passage and combustion chamber so the coolant turns to steam and out the exhaust it goes. No leaks, no milky oil just sweet steam out the tail pipe.

Try this. Re-fill the reservoir, start the car, warm it up and take a clean rag and place it over the exhaust for a few moments. Smell the rag. It normally won’t smell sweet. If it does, suspect a head gasket. Run a pressure test on the cooling system and see if it holds.

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Thanks! I will check that out soon.

Thanks! Checking it out

If you have a radiator cap you may wish to check the fluid level there, when cool of course.

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If you didn’t fill the radiator too, and burp the system, than you were driving around with an empty cooling system. The coolant is probably being drawn into the radiator when you shut the engine down and the air entrapped in the cooling system contracts.

My recommendation is to have this towed to a trusted shop ASAP. You need this assessed by someone with expertise in how cooling systems work. The system needs to be tested, the leak fixed, and the system refilled as a minimum. Hopefully you won’t be dealing with a blown head gasket. When that happens coolant gets drawn into the cylinders through the breech and blown out with the exhaust as vapor.

Let us know how you make out.

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Agree, you likely had an empty radiator and just putting a little in the tank just went right into the radiator every time. A few pints versus a gallon or so. That doesn’t mean though that you aren’t losing it some place in the first place like the head gasket. But there are other places you need to look at too when you get the system filled like water pump, hoses, leaky radiator, etc.

If you keep driving this car and overheating it, you could cause some expensive engine damage, as today’s engines often don’t tolerate this. Whether you’re able to fix it yourself or you need to get it to a shop, I suggest getting this fixed right away.

My coolant was disappearing. There was never a pool of coolant underneath. I was busy so I used a few of those leak-fix products (Bar’s was 1) and kept on adding coolant. Eventually I found a seal on my water pump broke; it leaked only while I was driving but little enough I didn’t notice a trail where I parked. I have a longitudinally-mounted engine so replacing it was a piece of cake (for a non-motorhead); I got a new one for $27 in-stock @ Auto Zone.

Thanks for all the input. The empty radiator makes sense. My mechanic is not open on the weekends but the plan is to take it in on Monday. The floor mats are not wet, I can’t find a leak or drip anywhere and I am reluctant to drive anywhere.

Good plan. I strongly urge you to have it towed rather than try to drive it. Trying to drive it to save the tow fee is a very poor gamble.

If you are losing coolant via a head gasket leak that quickly, you should be seeing some white smoke (steam) out the exhaust pipe. Some white smoke is normal on cold starts, but w/a head gasket leak you’d see it even after the engine is warm. Sometimes it only happens during accelerations so ask a friend in another car to follow you as you accelerate up a freeway on ramp. Also check for coolant accumulating at the lowest part of the vehicle; usually that’s the trunk well where the spare tire is kept. You may find a little diving pool there :wink:

Oh come on, how is that even possible. Coolant going to engine because of head gasket out tail pipe . Leaking anywhere in engine compartment is going to fall on ground .

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