@$#&*! expansion tank cap

gull · Post by **gull** » Fri Aug 18, 2006 9:57 pm

I'm really just venting here (no pun intended) but the expansion tank cap I bought only six months ago is already bad.

I was in stop-and-go traffic a lot today, and everything was fine until this evening when I drove home. The temperature just wasn't coming down like it normally does when I resume speed -- in fact the more I stepped on the gas, the more it wanted to creep up, although it never really overheated. I fretted about it all the way home. Poking around the engine bay, I noticed some vented coolant around the tank (not unexpected, since I'd been running hot) but something was nagging at me. Where had I seen this behavior before? That's right, the time I forgot to put the cap on. I squeezed the upper radiator hose and, sure enough, no pressure at all. Carefully removing the cap confirmed it -- plenty of coolant, but no pressure.

New cap. Six months. Dead. Sheesh.

Post by **Calimus** » Fri Aug 18, 2006 10:35 pm

I've had similair issues when buying the caps from the local auto parts stores. Bought a dealer cap and 3 years later, no problems.

gull · Post by **gull** » Fri Aug 18, 2006 10:40 pm

Maybe I'll try the dealer, then, if they have one in stock. (My other car is in the shop, so I have to drive this car to work on Monday.) The faulty cap came from The Bus Depot.

gull · Post by **gull** » Sat Aug 19, 2006 5:02 pm

Got one from the dealer. They had it in stock, which amazed me. They normally give me a funny look when I ask for parts for my 17 year old car. I compared the two caps; the dealer one had a completely different, and much more robust-looking, valve arrangement.

Post by **Briano1234** » Sat Aug 19, 2006 5:59 pm

I know, I know... the cheap high vis years they keep in stock. funny I went 20 years with my diesels cap, but then again I went through 3 jugs.

Now on this cabby I am on my 3rd jug and second cap.

Time will tell.

gull · Post by **gull** » Sat Aug 19, 2006 10:18 pm

I probably shouldn't have replaced the one that was on the car when I got it. It was old, so I replaced it on general principle. I bet if I'd left it alone it would have been fine.

Post by **Briano1234** » Sun Aug 20, 2006 2:40 am

What is tha told addage? If it's fixed don't break it? LOLOLOL been there done that.

sixsracing · Post by **sixsracing** » Mon Aug 21, 2006 2:55 pm

Usually if a vehicle is overheating at speed the radiator is compromised. More often than not the fins are all gone. How's your radiator look?

Post by **Briano1234** » Mon Aug 21, 2006 3:24 pm

sixsracing wrote:Usually if a vehicle is overheating at speed the radiator is compromised. More often than not the fins are all gone. How's your radiator look?

That is why I bought a new jug, because with a clean engine the old yeller one is ugly, and the new jug I got from parts4vw sprung a leak about 3 months later. So I got one locally from a different source than the dealer and it is heavier and is almost transparent where I can actually see the level of the fluid.

This time I bought a new cap too. So it is a wait and see kinda thing...

gull · Post by **gull** » Mon Aug 21, 2006 5:54 pm

sixsracing wrote:Usually if a vehicle is overheating at speed the radiator is compromised. More often than not the fins are all gone. How's your radiator look?

Actually the car has always run nice and cool at speed -- just below the LED on the gauge. That's why I knew something was wrong when the temperature started to creep up all of a sudden. I don't know why a lack of pressure in the cooling system causes this, but I've seen it on other cars, too. My pet theory is that the lack of pressure causes localized boiling in the head, limiting heat transfer. At any rate, with the new cap on it's back to running cool again.

sixsracing · Post by **sixsracing** » Tue Aug 22, 2006 8:45 am

There is pressure in the cooling system because waters boiling point is higher than 212 F under pressure. Remember your Mom's old pressure cooker? Same concept.

Post by **Briano1234** » Tue Aug 22, 2006 5:41 pm

sixsracing wrote:There is pressure in the cooling system because waters boiling point is higher than 212 F under pressure. Remember your Mom's old pressure cooker? Same concept.

I can remember my momma shooting beef stew all over the kitchen in one of them things.... My dad said it was an evil plot of hers to have him redo the kitchen....(which he did)......

There was beef stew hanging from the ceiling light.... tooo funny a rememory.... Thank you.

gull · Post by **gull** » Tue Aug 22, 2006 7:07 pm

A friend got 2nd degree burns and his finger broken when one exploded. It was an old thrift store one, though, and they were (ab)using it as a whiskey still...