jjaaam

To make a long story short, all of a sudden my 2003 overflows coolant out from under the surge tank cap when I shut it off...intermittently.

When this first happened before a month ago I got a new surge tank cap. All seemed to be well until last Friday. Was letting it idle while working on something and, when I shut it off, it overflowed on the garage floor.

Thinking (hoping) it was an air pocket problem I did my best to burp the system per the procedure I've seen posted here. Took it on a short drive Saturday. Temps solid between 194 and 198. Got home and no issues.

Drove 70 miles to work this morning. Again, 194 - 198 all the way. With a few stop lights and stuff once off the expressway it creeped up to 212 before I got to a parking space. Shut it off and sure enough, it overflowed again.

I'm getting frustrated! Is this a sign that I have a head gasket problem? My oil does NOT look milky, nor is there any sludge on the dipstick. And, to note, it has never overheated or overflowed on the road while driving. Always solid at the same 194 - 198. Only happens when I shut it off. I even tried to bleed air out of the heads per the procedure that 8VETTE7 had posted with loosening the coolant crossover tube.

Any ideas before I take it in to the dealer? Could the surge tank itself be bad somehow?

Thanks...

runner140*

It could be as simple as needing a new pressure cap. That's where I would start. You might need to replace the surge tank....both are not expensive, easy to install and should do the trick. Most auto parts stores will test your system for the correct pressure and sell you what you need.
The test is free, parts are not. Get back to us.

P. S. Stay away from the dealer. You should have learned at least that from the Forum.

jjaaam

Thanks for the reply.

As I noted above: "When this first happened before a month ago I got a new surge tank cap." That seemed to work for a bit but it isn't now.

Yes, I HAVE learned that about the dealer...but I'm concerned that tracking this problem down is beyond my capabilities, unfortunately.

How would the tank itself be the issue? I see absolutely no leaks or cracks in it. What are the symptoms of a bad tank? Could the top edge of the tank that touches the seal on the cap be warped, therefore allowing pressure leakage when it gets above a certain point?

runner140*

Have it pressure tested....may repeat may not making good contact between (the neck) the surge tank and your new pressure cap.

P.S. Pressure testing is usually free at most auto parts stores.

jjaaam

OK...I looked up how to pressure test a C5.

Here's my question - since the pressure tester gets screwed in where the surge tank cap goes, is it correct to assume that if it leaks from around the cap area when pressurized that the neck on the tank is probably warped and not sealing with my new cap? Looking at the tank it seems to be the original one...so if I got a new tank that would be the answer?

I have never had any cooling issues at all until this came along. Again, no overheating while running and no visible leaks/smells anywhere else.

I'm just wondering if I should get a new tank. Dorman has them for $60. Change it out myself.

If something was really bad like a head gasket wouldn't that apply extra pressure especially when running, and cause the overflow from the cap while driving?

Sorry for all of the questions just trying to logically figure it out.

Thanks...

jackthelad

Pressurizing the coolant. i.e. head gasket or similar failure is guaranteed to produce what you are seeing. Are you also losing coolant? If so, that's your problem.

jjaaam

No, sir...I'm not losing coolant. I only lose it when it overflows...LOL. I haven't had to put a drop in it since I got it two years ago. It's just now with this overflow issue that I'm having the problem.

And, my oil looks fine. Not milky at all, and no sludge or anything else on the dipstick.

Again, looking at this from a logical standpoint:

The pressure cap I have is rated for 18 PSI. I'm assuming that means if the system pressure gets over 18 PSI then the cap will allow coolant to overflow (exactly what I am seeing when I turn the engine off on an intermittent basis).

I also would assume that more heat = more pressure. That would 100% explain why, if my old tank neck/new tank cap seal is marginal, that it WOULD overflow when it gets hotter. Normally I park, shut it off, and all is fine. It's seeming like it only overflows when the heat is above my normal operating temp of 194-198. This morning it was at 212 while waiting for traffic and driving slow through the parking lot. It did it before when I was letting it idle while investigating other issues...therefore, again, the heat being over the normal operating temp.

**OR**

Let's say it IS the head gasket. While running at normal speeds the airflow from the radiator may keep the temps low enough where the pressure doesn't exceed 18 PSI, even with increased pressure on the system from the exhaust fumes. If it gets over normal temp (idling or by slow operation) and THEN I shut it off then the pressure has to go somewhere...so it overflows.

Here's the big question if everything I've assumed is correct - if it WAS a head gasket then wouldn't the pressure be too high every time I drive it?

Am I overthinking this?

jackthelad

If what you have is a simple gasket "fail" from cylinder to water jacket, nothing would be getting in the oil. Are you seeing any white smoke when you drive it hard? White smoke = water in the exhaust. The only way to be sure is to do a compression test - leaking gasket will typically have one cylinder at a lower pressure than the others.

The other thing that can cause C5 cooling trouble (and overheating) is the radiator - C5's are bottom feeders and the radiator can accumulate dirt and debris.

I just did a Google search on C5's and overheating - there are a number of posts on the topic across multiple forums.

jjaaam

Thanks to everyone for the replies, not only to this thread but to PMs as well.

I think I'm just going to get a new tank. I'm positive it's original...can't hurt, and the Dorman ones are only $60.

Thanks again!!

lar66BB

Just a thought you may have a thermostat that is only partially opening.

jjaaam

That would cause the boil over when not running? Temps are fine when driving at normal speed. Wouldn't a bad thermostat make it overheat while driving?

runner140*

My post #2 covered this.

sirdano

Hum I bet it is the cap.

I left mine off one time and I power flushed all my coolant out the overflow tank since there was no cap. So my thinking if there is a leak it is going to push it out were it is weakest.

sirdano

Nope read it just thought maybe he got a bad part. China????

jjaaam

Cap was new.

Just got my new tank today. Will be putting it in tomorrow...so hopefully that cures it.

jjaaam

Installed new tank. Bled air at the heads. Tried to follow the "burping" procedure but it will NOT go over 201 deg...even revving it up at 3000 rpm for 30 sec intervals. Actually, the temps go DOWN to 196 or so when I rev it.

What is going on?? Usually letting it idle takes it WAY over 200.

Doesn't make any sense...or does it?

Took it for a test drive and pulled over at a gas station and let it idle. Now it started heating like "normal". I let it get up to 225 then I shut it off. It didn't overflow...

So hopefully the tank was the problem after all. Will monitor it and see.

Pounder

Thanks for posting results

jjaaam

Today was the acid test...drove it 70 miles to work. Never got above 199, even with waiting for traffic lights once off the highway and going slow through the parking lot.

I waited after I shut it off and no overflow. Popped the hood and I couldn't hear any hissing either...so I would assume that the pressure was equalizing properly.

Praying that the new tank was the answer!

jadoux

Sorry for jumping in late, I experienced something similar with my 04 A4 coupe, and the tank was the culprit, but i changed both the tank and the cap, and never experienced a problem with it

There is a hose that connects to the tank from beneath it, and that curve there used to have an amount of sludge that blocked around 25% of the flow, ever since i changed it, along with the cap (because i suspected that the pressure wasn't holding 100%) everything went to normal and I was never able to bring the car back to those high temps that used to show on my dash

I suggest that you keep an eye on it, but most probably your problem is solved

jjaaam

I sure hope so. Having problems like that can be very frustrating! It's comforting to hear that someone else was having the exact same issues and that the fix wasn't a major repair...