chronic coolant-expansion-tank-cap-itis

As I was reading the post I thought OK, new engine so maybe not with a head gasket problem. I was thinking that there must be something you are doing with the antifreeze mix. I do a 50/50 and never had problems with hot or cold temps.

There is a way to take the caps apart and make sure the little hole in the top is allowing air in when it should and holding back the pressure when that is needed. I disassembled the one on my Rabbit and found it to be pretty dirty, even though it was working I was getting concerned about it.

Even if it is a new to you engine I would still be doing a compression check on it just to be on the safe side. That can be done real easy too. Just take one of those mechanics gloves or latex gloves and put it on the expansion tank in place of the cap. Do this prior to starting it up cold. Then start the engine gentleman! In about a minute do you see the glove starting to inflate? Likely that is caused by the air coming in from the cylinders and thus you have a leak on the head gasket.

Food for thought or an excuse to be under the hood.

ORCoaster said:

As I was reading the post I thought OK, new engine so maybe not with a head gasket problem. I was thinking that there must be something you are doing with the antifreeze mix. I do a 50/50 and never had problems with hot or cold temps.


Even if it is a new to you engine I would still be doing a compression check on it just to be on the safe side. That can be done real easy too. Just take one of those mechanics gloves or latex gloves and put it on the expansion tank in place of the cap. Do this prior to starting it up cold. Then start the engine gentleman! In about a minute do you see the glove starting to inflate? Likely that is caused by the air coming in from the cylinders and thus you have a leak on the head gasket.

Food for thought or an excuse to be under the hood.

Click to expand...

This test is a winner for Head Gasket Failures, and they can occur at any time, as I used to run a Diesel that would blow one every 6months because of the bolt issue on the engine.

The CAVEAT is that you tie the Glove tightly over the open Expansion tank.
You have to Start the engine, then REV it above 3000K for 45-50 seconds any longer and the Glove will Auto Inflate from the heat and steam of the a/f.
If the glove inflates and gives you the finger, then you have a blown head gasket. On Gassers it can either be a blown head gasket, or a leaky water jacket oil cooler.

Another indication of a head gasket failure is that your Hoses will Balloon and be hard to squeeze but once the engine stops your Hoses return to normal.

Easy to see on a running engine that is warm.

If you do have a Head Gasket failure then I would strongly urge you to install the ARP stud kit.
These kits are re-usable and they when installed usually won't loosen and take care of the bolt loosening issue that the 1.5 engines can be prone too. If when I had found this out, (back in the Pre-Al Gores invention of the internet) I would if installed these. The Head Bolts are not re-usable they are a one time use only. They also have to be re-checked for torque at about 500-1000 miles. I suspect the best thing is that I got really really quick at changing the head gasket. I will also suggest that you place the engine in time prior to diss-assembly.

Causes of the Expansion tank issues (and Caps) is two fold, a blown head gasket or Crappy parts.
I just went through this on one of my Cabriolets, where the Cap wouldn't tighten down.... new tank and cap later (bought as a pair from O'Reilly's) worked.

I did the head gasket dance a couple times with the original 1.6D back when I first bought the car in 2010. the block had already been helicoiled, so I got into custom machining threaded inserts... what a nightmare. in 2012 I decided to spring for a 0 mile 1.9 naturally aspirated diesel complete conversion engine called 1Y, designed for the 1990's European Jettas if I remember correctly. its been a charming upgrade. im not super concerned with head gasket issues as I have been babying this new engine ever since with regular oil changes and modest driving habits, but I do love the rubber glove test, I may do it anyway.

the expansion tank is a new(in 2012) Meyle, and I even got a second one thats on the shelf in my shop out of fear that the threads on my current one were the culprit to my leaks. I have found that after a few months, tightening the cap becomes a delicate operation that involves avoiding over tightening, as they start reaching a maximum torque (by hand) and beyond that get loose again as if they were stripping. new caps don't do this, they don't start skipping a thread when you go too far, they just get too tight to go any further, which is what I like to feel to know im done tightening.

the coolant I run is 50/50, always. the climate im dealing with these days in the Adirondacks is averaging between 0 and 25 degrees Fahrenheit. hottest summer temps average between 65 and 85.

Just as an experiment, I hooked up my new meyle expansion tank that has been on my shelf for 8 years, and I sealed it with a 6 month old cap that had been badly leaking prior. The old cap works fine with its new tank friend, no leaking as of yet!! This leads me to believe that the threads on the expansion tank, which look pretty fine on the tank I just replaced (except for the very first one that tapers to nothing at the top) are indeed the culprit of this chronic sealing issue.

Lesson: baby your expansion tank threads everytime you take the cap on and off, but especially when putting the cap on, by making sure the cap is going on properly, feeling the threads mesh with absolute ease. The first thread is more important to achieveing the proper torque for the cap’s sealing function than I ever imagined, and it’s the first to be deformed. Perhaps a creative alternative to replacing the tank could be to hack saw the top centimeter off the tank fill hole to get back down to good threads that won’t skip. The trick there would be tapering the first thread and making the lip nice and smooth and flat after the hack job, to mate properly with the squishy o ring on the cap.