VW MK4 JETTA - figuring out coolant leak mystery 

You just saved me a complete radiator replacement!!! My top hose was split, but I thought it was split on the radiator side, as part of the radiator. It was actually split on the host clamp that you pulled the clip out of. Your close photography of this part and going through the whole system, and having very good video and very good instructions bailed me out!!! THANK YOU!!!

Did you check the coolant flange with the ECT sensor? They can warp and cause a very very very small leak that might not be noticed because it gets burnt off when it hits the transmission. A telltale sign of this is having a white flaky looking crust on top of your transmission it'll also resemble like a pink tint if you're using the pink or purple coolant.

I got a 1.9L PD engine. When the front end is raised up the leak seems to be dripping from the front-most hole on the frame rail. I put in a new heater core and a new cooling pump to solve this issue but I still have the same issue.

Great video. Can you remember what size barbed joiner you used ? I've got a mystery leak on my TDi too...

I’m having a similar issue on my 02’ alh. I get excessive pressure in my upper radiator hose then coolant leaks from the upper radiator hose where it’s attached to the block/coolant glow plug housing. replaced the hose clamp, no luck. Replaced the thermostat with no luck. Replaced the cap on the expansion tank with no luck either. I just tested Head gasket with the special blue fluid and it was fine. I’m not getting a constant flow from the return into the overflow bottle, even after 2 cycles of “heating it up to temp” while pumping/squeezing thermostat coolant hose and upper radiator hose, capping it and letting it cool down to draw coolant in. I put up to temp in air quotes because it wont get to 190. I do have heat strangely, but it will drop the temp slightly when on. Im curious if i have an airlock or clog in my system, either way, would a flush be the best move or am I overlooking anything? Any help is appreciated.

I have a coolant leak behind the engine on the firewall just under these two hoses going into the firewall where you pointed If the heater core it bad would it leak in the same area or inside the car. My heating works but I'm adding coolant quite often.

Question: will this cause the AC not to work? I knw with some cars, the AC don’t work when you’ve bypassed the heater core because the car temperature is too cool as it should run on a temperature. Did this happen when you bypassed the heater core or the AC still work as normal?

Check your oil cooler & the 2 gaskets. This is a cheap repair & the oil cooler failure can cause the antifreeze to slowly leak out. You can grab an oil cooler for around $25 online.

Interesting that the inlet side of the heater core connection was clean and the outlet side had some gray particulate on it... I wonder if that is an easy quick diagnosis for a probably failed heater core?

TIP... tie some fishing line to those clips on the hose joints,,, that way you won't lose them as they can go flying if you snap them open too far or fast... it happened me ,,, loosing 2 of them,, then i thought of the fishing line. also you should have coolant in the car if the core is leaking,, wet carpets ...

My vr6 is leaking as well. But the leak is running from somewhere on the same side as the reservoir. And suggestions? I seen it running down the side of the oil pan so that was my first assumption. The reservoir needs to be replaced because the return hose fitting is broken but idk if that would cause such substantial leaks when it sits. Maybe though. Thanks for the vid 🙏

jury rig an old radiator cap with a tire nozzle tip and let her fill up with air...dont worry that a line will burst , THAT is actually your intention.

Should be a steady flow coming from that hose on coolant tank once bleed if not you have a restriction, possibly bad water pump.

Thanks so much for this

I have a coolant leak in my 2000 tdi jetta right under the bumper passenger side.. waiting for a bit warmer days to dive into it

Did you check Waterpump? It looks like there is no circulation, you can easy check removing Thermostat housing for waterpumpimpeller it can separate from pump shaft.Btw i have the same car with same Engine.

VW touareg tdi 2009 what if you have to fill up coolant bottle of 2 to 3 liters every 20 or 30 miles, but after checking: coolant sensor, heater air and everything else plus engine not overheating, i noticed coolant leak from the evacuating hose from the bottle at the bottom of the car.? What could be the problem? Thanks

where do you obtain the plastic barb fitting from?

Very good video. Thank you.

I have an 02 vw Jetta 2.0l that leaks coolant just as bad as that wonder if it's the same thing is the heater core even a vital component of your vehicle?

You forgot to putt the clamp back on the small hose in the reservoir.

Hello thanks for your video, I have a problem where I was loosing level and gaining pressure in my coolant, I first changed my expansion tank and cap was still getting pressure, I'm currently at the point where I have bypassed the heater core and looped my 2 pipes together, The level now hasn't gone down so now I'm thinking time to change the heater core I was thinking maybe it is blocked so I think I will try clean my heater core and go from there, What was your end result did you replace the heater core and did it fix the problem? Thanjs in advance 😊👍

Question can you put actual water in that there coolant bottle only water I mean ?

Did you ever figured out where the leak coming from?

thank you

My friends 2004 jetta is leaking lots of coolant we replaced one of the heater core connectors because it was leaking but it did not fixed the problem. Tomorrow we will inspect it again but this time I will try my best to check his water pump, base on your responses it seems the heater core replacement did not fixed the issue and now it’s been over a year, what was your leaking issue and what did you replace to solve it. Thank you very much!

What will happen when the radiator is open you press the gas pedal

Ever figure out the problem?

What is problem bro ?

Did you solve the problem?? any updates? Thank you

What if u do have the creamy nastiness?