Coolant Leak: Thermostat Housing Pipe Replacement.

Hello everyone!

It actually happened to my Golf 4, engine code: AHF, it's leaking!

To provide some background, after a long drive on the highway, I noticed a coolant leak in the expansion tank!
Water level was at its minimum!
At first glance, nothing seemed amiss, as the engine cover and most of the hoses are visible. There were no obvious signs of damage; I had previously found a bite mark on a hose connected to the heater core, so I was expecting something similar.
'That wasn't the case. After removing the cover, the mess was immediately visible. There's a leak coming from the metal tube, which is inserted into the thermostat housing with an O-ring (???), and is fastened to the cylinder head under the vacuum pump with a screw. The 10-pin fuel injector connector, the connection to the NBF (presumably a sensor or module), and another connector are also attached to this tube.'
As well as further cross-connections of the cooling system!

Now comes the tricky part: how am I supposed to get the pipe out of the flange without disassembling half of the engine beforehand?
Normalerweise, um da vernünftig Platz haben zu wollen müßte die ESP plus Aggregateträger, der Ölfilter mit allen Anbauteilen und was weiß der Himmel noch ausgebaut werden, da das Rohr noch seitliche Abgänge hat, die spätestens am Ölpeilstab anschlagen! Wer hat Did someone invent that?

The first alternative is a radiator sealant, but I don't think that's a good solution, and I've seen reports in various forums that confirm this! Overheating of the engine when frequently towing a trailer.
Second option: Pull the pipe out as far as possible from the fitting, apply Hylomar or a similar sealant, push it back in, and hope that it seals!
In my opinion, this is the most sensible method. If that doesn't help, then sometimes things just happen.
Third option, see above.

Has anyone else encountered this problem? I would appreciate any tips!
Best regards, Ferdi.

Hi,

The coolant hose can be pulled to the right, and then the O-ring can be easily removed and replaced with a new one.
Expanding and checking the entire pipe system would still be advisable. In my opinion, one should 'only' remove all the components of the glow plug auxiliary heater on the cylinder head.

Best regards, Rainer.

Hello Rainer,

Thanks for your tip, I'll take another look.
The glow plug heater gives me the fewest problems; I'm more concerned about the cross bracing of the pipe!
Okay, you can remove the upper part of the dipstick, which would get you a little further, but then you'll encounter the flange of the oil filter!
Or is it possible to rotate the pipe so that the cross pipe eventually stands vertically, thus bypassing the oil filter?
I need to check that out and probably end up hurting my fingers tomorrow!

By the way, Rainer, just out of curiosity, what is the fuel injection volume of your AHF engine at full load, at 4200 RPM, on the dyno?
I logged the current fuel injection amount, as well as the measurement group for the three lowest fuel injection amount values.
The lowest value I always see is the torque limit, which is between 38 and 40 mg/H!
Is that correct? It seems a bit low to me, as 'Fahrerwunsch' implies something more!
That would also confirm my driving experience, that the power is reduced starting at 195 km/h according to the speedometer!
Or maybe my speedometer is so accurate that it simply stops at 195 km/h, and I'm driving into the torque limit, because the tachometer is showing 4300 RPM!

Have a nice weekend, best regards, Ferdi.

Hi Ferdi,

Certainly, the foot is more willing than the ESP – meaning it's normal for the actual torque to be below the driver's desired values.

My foot/GRA also easily reaches up to 45 mg/H, but the stingy 1Z controller cuts off at 35.2 mg/H... but it doesn't know everything.

m;