What could be the problem?!?!?!?

[phaetonv10]

Hey guys.

My mk2 gtd is running great.
But there is something wrong in the cooling system. The fan comes on at the right time and it doesn't overheat. The problem is that as soon as it reaches normal temp, the coolant warning light starts flashing.
If I undo the expansion tank cap when the car is running and at normal temp, water starts to bubble out. Should it be doing that??
I was suspecting a blown head gasket, but I don't see any symptoms of a blown hg like oil mixing with coolant, or water traces in the oil.
Though my coolant is full of rust. I would also like suggestions on how to rid of that.

Cheers

[TylerDurden]

I presume the coolant is proper mix with water. 50/50 is typical.

The fan indicates that coolant is flowing properly through the radiator. But, are the radiator fins clean, so air can pass through?

I had a failing HG with similar symptoms. It was hard to tell, even with a test for combustion gasses in the expansion tank. Replacing the HG solved the problem.

[libbydiesel]

If the engine is hot it is normal for the expansion tank to overflow if you open it. 

I would assume the light is blinking because your coolant level sensor is confused by the rust in the coolant.  Flush the system and refill with proper coolant mix and your issue will likely be solved.  FWIW, coolant should be changed every 2-3 years.  If it is actually causing rust in your system then all the buffers in the coolant have been gone for a long time and all the parts of your engine touching the coolant are being dissolved and being reconstituted in your radiator.  It's very expensive to not change your coolant regularly.   

[phaetonv10]

Just flushed the whole system. Took a small test drive and the warning light didn't flash.
Tomorrow's morning commute would be the more rigorous test.

I ve ordered head gasket anyways. The aaz metal hg.

And I think it ll be a good chance to replace the standard head bolts with arp head studs.
I ve had these head studs lying around for years now.

[Toby]

Though my coolant is full of rust. I would also like suggestions on how to rid of that.

The ONLY time you get rust in a cooling system is when you get acid in the coolant. That only happens when combustion products enter the cooling system. This means leaking head gasket. You can tell how much acid is in the cooling system by checking coolant voltage. With a DVM set on the Mv scale (.001 vdc) take a reading between the coolant and something brass in the cooling system, like the radiator (if its brass) or a coolant temp sensor. It should read well below .200 volts. If its above .400 Vdc you have problems with the acid and it s eating aluminum parts of your engine. And you have a bad head gasket. This test is definitive.

[libbydiesel]

Toby that is not true and bad advice to boot.  You get rust any time the chemical buffers in the coolant are used up.  While combustion gases will cause that to happen faster than normal, it will still happen as coolant gets old.  The head gasket is also not the only way for combustion gases to enter the coolant. 

[Toby]

Toby that is not true and bad advice to boot.  You get rust any time the chemical buffers in the coolant are used up.  While combustion gases will cause that to happen faster than normal, it will still happen as coolant gets old.  The head gasket is also not the only way for combustion gases to enter the coolant. 

You are absolutely incorrect on this. RUST = Bad Head Gasket. Disbelieve it at your peril. Pure water in a cast iron motor won't get rusty to any appreciable degree w/o acid in the cooling system. Acid caused by the reaction of combustion gasses with water. In 45 years I have never seen rusty coolant that was not acidic. It is easy enough to find out. Just check the coolant voltage.

BTW please name another way that combustion products enter the cooling system, (except for a crack, of course, which is almost always caused by overheating brought on by a bad head gasket)

[TylerDurden]

Errrm... acids don't attack aluminum, alkalines do...

"Simply stated, pH is the measure of the degree of acidity or alkalinity in a coolant. The acidity decreases and the alkalinity increases as the pH goes from 0 to 14. The recommended pH range for coolants is on the slight alkaline side, from 7.5 to 11. Anything at 11 and above would be considered too high. Tests that range from 6.0 up to 7.5 would be considered too low. The pH of fresh coolant slowly decreases with time and use in a cooling system as acids are formed by the oxidation of ethylene or propylene glycol. At low pH ranges, certain metal surfaces are susceptible to acid corrosion, while at high alkaline pH, aluminum surfaces are susceptible to corrosion. Thus, it is important to check the coolant pH periodically to make sure that it is neither too acidic nor too alkaline."

http://www.cooltrak.com/faqs.asp

[libbydiesel]

Toby I have personally seen rusty coolant in a vehicle that did not have any head gasket issues whatsoever.

Cracks in the head or block can cause combustion gases to enter and again, I have personally seen them occur without overheating or head gasket issues.

My best guess as to why you haven't seen those things is perhaps in your 45 years you have only seen what you decided to see, and backed it up in your own mind with incorrect information that you believed to be true.  45 years of believing something that is wrong doesn't make it right.  

[Gizmoman]

Just flushed the whole system. Took a small test drive and the warning light didn't flash.
Tomorrow's morning commute would be the more rigorous test.

I ve ordered head gasket anyways. The aaz metal hg.

And I think it ll be a good chance to replace the standard head bolts with arp head studs.
I ve had these head studs lying around for years now.

So, how did your morning commute go?

Also, is the HG you ordered the same as the one you have? As this sounds like it may be your daily driver, I can understand why you would want one on hand as they are not that easy to obtain (especially the one notch). There are three different thicknesses and the best way to find out what you need is to measure piston protrusion. Here's a quick link to the info from the FAQ http://www.vwdiesel.net/forum/index.php?topic=6741.0 Having the wrong thickness can either damage the engine (too thin) or make it tough to start (too thick).

[srgtlord]

oooor the sensor is fubared

[phaetonv10]

It went ok. But the hg is on its way out. My conclusion is based on the fact that the rubber coolant pipes get hard as wood. So I think the combustion pressure is leaking into the coolant jacket.
And the rust is back. I flushed the system 3 times before I refilled it. And 2 days later, the rust is back.
Hopefully the new hg, arp studs will solve the problem.

[Gizmoman]

Agreed, sounds like your on the right track.

Keep us posted.

[libbydiesel]

The hoses do normally get hard.  Normal coolant pressure is 14-15 psi.  An easy test for combustion gases is to let the car sit overnight, open the expansion tank cap to normalize the pressure, replace the cap, run the engine for 30 seconds and then loosen the cap while listening for the sound of pressure escaping.  If there it is pressurized, combustion gases are likely.  Any flaps will also have a kit for testing for combustion gases in the coolant. 

[phaetonv10]

Hey guys.
It's finally done. MLS HG, ARP studs.
It wasn't all smooth sailing though. When I removed the head, it was in bad shape. The water ports around cylinder 3 were all rotten. But luckily I had a spare head lying around which was in great shape. Put that on. And it's been smooth sailing since yesterday.
Put in a new speedo cable too, speedo still doesn't work. I don't think the speedo is bad though.

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