coolant disappearing but no leak?

[ff54976]

1.8t auto. I have checked the rear coolant flange, the j plug, expansion tank and no leaks. I looked at the radiator but once again no leaks. Theres no water in the oil. car idles fine. car warms up normally. no motor problems. My heater only gets warm and not hot, and at idle it goes from warm to cool. no leaks found inside the car, no sweet smell either. i didnt know if this was related to the coolant disappearing or no. It is possible to lose coolant through the oil cooler and not leak? Im been scratching my head for weeks now reading thread after thread.

[B44]

You might have air in coolant leading it to not heat. This might be not accurate but I read on one of forums where you remove the coolant cap and start the car and on the heat and the coolant burps giving out all the air bubbles stuck in the system. Second option it can be your thermostat.

[blitz2190]

to check if the cooler may be leaking is easy you would find "water" droplets on the dipstick or a milky brown. If not a leakdown test may be in your future.

[jacobsen]

You may have an air bubble and the coolant is finally filling and displacing the air. If you seriously don't have a leak you know you have a head gasket leak. Check piston heads for cleanliness, I'm guessing that your radiator is leaking, IF you checked every thing else. This is a pressurized system, so that might now show until high pressure. Check, check, check it again and check it again.

[ff54976]

I have already tried leaving the cap of the expansion tank but no bubbles or burping. My oil cooler is leaking oil but it only looks like oil and not oil coolant mix. Pressurizing the system is a good idea, that way if I still don't see coolant then I'll start going down the motor path. Only thing is car runs fine, doesn't overheat, no white smoke out the tail pipes. Would I be able to see a leak if it was coming from the thermostat housing?

[B44]

Check thermostat most like it's that after what you said. Also if you were leaking coolant in the head you would have acceleration hesitation and white smoke.

[lookaught]

You can also pull the plugs and shine a light into the cylinders, if you're losing sufficient coolant through the head gasket youll see one or two clean pistons, steam cleaned by the water.

[surfer1037]

I chased a coolant leak all last summer and could never find it as it wasn't dripping anywhere, until I opened the coolant tank after a spirited drive, very hot, and it started pouring out of the j-plug and thermostat. Just an idea to check

[xhackerekx]

cracked head or gasket for me.

[ff54976]

I will be looking at the car today and I will report back.

When I checked the car in the usual places for coolant leaks the rear flange showed that it has leaked heavily on the back of the motor/top of the transmission by getting that orangey color all over the place. The rear flange is brand-new though so I know that's already been fixed. I have the same orangey color everywhere underneath the J plug but I was watching the car with the motor on with someone holding the accelerator down and I was not seeing any coolant leaking out of the J plug even though there are signs that it has or does leak from there.

I will look at the tops of Pistons aswell.

[Jborch8]

I will be looking at the car today and I will report back.

When I checked the car in the usual places for coolant leaks the rear flange showed that it has leaked heavily on the back of the motor/top of the transmission by getting that orangey color all over the place. The rear flange is brand-new though so I know that's already been fixed. I have the same orangey color everywhere underneath the J plug but I was watching the car with the motor on with someone holding the accelerator down and I was not seeing any coolant leaking out of the J plug even though there are signs that it has or does leak from there.

I will look at the tops of Pistons aswell.

I replaced my coolant flange (and temp sensor) on my 1.8t last year to remedy my coolant leak. Woke up in the morning to see my reservoir empty. Turns out the O ring just fell right out when I installed the new flange. I saw it sitting right on the tranny the next day after taking everything apart again.
May just be a freak accident in my case.
My first though is to thoroughly investigate those areas with the dried coolant marks. Seems to point to something.

[ff54976]

I checked at the heater core, nothing. But after I drove for a while then popped open the hood the expansion tank was hissing. It that normal??

[diagnosticator]

I checked at the heater core, nothing. But after I drove for a while then popped open the hood the expansion tank was hissing. It that normal??

The tank cap has a pressure relief valve inside, to vent cooling system overpressure. If the cap was hissing, the cooling system pressure was to high, and that is not normal.

It is also possible the tank pressure relief valve is defective and leaking, but considering the other symptoms, that is unlikely.

[diagnosticator]

cracked head or gasket for me.

I have never heard of a 1.8T cylinder head proven to be cracked with leaking coolant from cracks in the head. Therefore, all of the allegations frequently passed around here on AZ or from any other sources blaming coolant leaks on cracks in 1.8T cylinder heads are only unsubstantiated hearsay, with no basis in actual fact.

[Jborch8]

I checked at the heater core, nothing. But after I drove for a while then popped open the hood the expansion tank was hissing. It that normal??

The main struggle here is the lack of room/visibility of where the leak may be coming. One thing that really helped me was using my phone in video record mode (with flash enabled) and doing a recording of the back of the engine. I was hoping I could see if my coolant flange was the source of my coolant leak. Sure enough, after playing back the video I could see clear as day the coolant droplets forming at the bottom of the old flange.
It's worth a shot if you can wiggle your hand (may take some disassembling) to the back of the engine with your phone.

Also, let us know the findings of your pressure test.

[ff54976]

Anyone else on the hissing? I have a 03 Passat that I'm going to switch expansion tanks and caps and see if that has anything to do with it, if not that's another thing off the list of problems.

[ff54976]

ok i was looking all over the motor and the usual leaking spots and i dont know whats different today over yesterday but my j plug had some drop under it. I am picking up my j plug tomorrow and we'll see if that works!!!

[jmcwayne808]

They have these things called mirrors lol ^

[lyates1987]

Have you checked the coupler on the hose that runs over the tranny?

[WB650]

I have never heard of a 1.8T cylinder head proven to be cracked with leaking coolant from cracks in the head. Therefore, all of the allegations frequently passed around here on AZ or from any other sources blaming coolant leaks on cracks in 1.8T cylinder heads are only unsubstantiated hearsay, with no basis in actual fact.

LOL when I get my head back from the shop I'll be sure to take pics. They originally wanted to do the pressure testing to see if it had cracks but they could visibly see at least one crack on my head so I ordered a new head