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Pressure can or just the seal ?

Well, after re-seating the seal in my pressure cap, I still get occasional coolant leaking. This only happens after arriving home and turning car off. The rad fan comes on OK, but after it turns off, the coolant level in my resevoir creeps up and sometimes dribbles out. I am still not sure if the fan is staying on long enough but I don't think this is the problem.

Others here have suggested to replace the pressure cap. I called my local VW dealer and it about $21 CND for the cap and $4 CND for the seal (which looks like an O-ring). My question is, do I need to replace the cap or can I just get by with replacing the seal only. Is there any other aspect of the cap itself which may have failed and contributes to my coolant leaking.

Many thanks in advance.

Reply to
sonodude
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Don't be so cheap and replace the cap. Or buy the $4 seal and if it doesn't work then buy the $21 cap.

Reply to
Woodchuck

Or, don't be a "dummy" since it might just be the overflow hole because there is too much coolant in the system.

:-)

Reply to
Peter Parker

Ahhhh, but you see in order to NEVER get coolant leaking out, the cold level has to be so low, the temp LED on the dash flashes when I start in the morning. Even if I keep the coolant level low enough to avoid the LED from flashing in the mornings, it will still leak occasionally. With the engine cold, I generally try to keep the level a little (a couple of mm) below the "min" mark on the reservoir.

Thus I think that the reason the coolant is expanding so much is that I do not have a properly sealing rad cap, and thus not creating enough of a rise in pressure to keep the volume steady. Remember your physics? We are essentially dealing with a pressure cooker here. In a closed system, if you increase the pressure of a liquid, you also increase its boiling point. Aqueous (water) liquids expand greatly as the approach their boiling point. Thus, the higher the boiling point achieved, the less volume expansion you get. At least, this is how I understand the process here.

BTW, you mention the overflow hole. I am not familiar with this. Where is it located? Does it have a valve? Is it always open to the air?

Reply to
sonodude

This is strange. See second comment.

This is the second comment. Too much pressure? Headgasket leak?

The overflow hole is behind the G11 or G12 badge on the reservoir which points to the upper strut mount. I can't see the cap being bad since it screws in tight and the threads are not coarse.

Reply to
Peter Parker

Please clarify. How does a headgasket leak lead to too much coolant pressure and collant overflowing? I don't see white smoke out the tailpipe, so I think my headgasket is OK. Am I wrong?

I am not familiar with this G11 or G12 badge. However, what is the path coolant takes to exit via the overflow hole. Is the pressure cap in this path?

Reply to
sonodude

I had similar problems with my 92 passat. Turns out a replacement of the thermostat and the reservoir cap fixed it. Better than new now. The cost of parts were 20 for the thermostat and 6 bucks for the reservoir cap.

The thermostat that was thrown away was less than a year old. I though it was good, but was failing closed or slightly closed.

The reservoir cap can be damaged by simply checking while hot apparently. The rubber seal can flip or become miss-placed. $6 is cheap reassurance.

Later.

Reply to
tosui

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