Cracked block?

[ColinBurger00]

Can someone tell me the tell tale signs of a cracked block?

[ddillenger]

Can someone tell me the tell tale signs of a cracked block?

A cracked block usually presents with cracks on the block.

[Timtheguru]

Leaking fluids, low compression, visible crack... kind of a weird question, as we could throw out a ton of different scenarios that you might apply to your situation. What are you experiencing?

[LordO]

Coolant in all the wrong places and loss of compression.

[Letsride]

Depends on where the block is cracked!

[ColinBurger00]

Well, I called the local VW mechanic because I just recently changed out my rear coolant flange, thermostat (cuz I had no heat) and heater core, just cuz. I also went a bit over my head and did a big SAI delete, PCV delete, etc and Im not sure if I have everything hooked up right... anyway back to "my" symptoms.
I am currently having a sputtering idle, almost sounds as if the car will stall out but doesn't, I have heat when I turn on heater and my car does not go past 50% on the gauge so I am not overheating. however, I am getting the coolant light coming on saying low coolant, and when I lift the hood and open the reservoir slowly the coolant flows right back into the reservoir filling it up and all of a sudden I don't have low coolant anymore????

Mechanic thinks this sounds like a cracked block, and claims its "very" common on the A4

[Timtheguru]

Is your oil milky? Is your coolant oily? Sounds like you have a big air bubble, as far as coolant goes.

Sputtering could just be the fact that you have changed the vacuum routing to who knows what.

[ColinBurger00]

Is your oil milky? Is your coolant oily? Sounds like you have a big air bubble, as far as coolant goes.

Sputtering could just be the fact that you have changed the vacuum routing to who knows what.

no visible oil in coolant, cant see anything on dipstick either?

[diagnosticator]

Cracked blocks are not common on our A4s. That is something that is claimed when the mechanic doesn't know what is wrong. It can happen, but it is very unusual when it does, and is almost always due to freezing of the coolant in the cooling jackets. I have experienced only one case of a crack in a cylinder wall, in a 5 cylinder DE block.

Modifying the crankcase ventilation system was a bad idea. Now, you have problems. You should reinstall the PCV system hoses you removed.

[b6_quattro]

Is your oil milky? Is your coolant oily? Sounds like you have a big air bubble, as far as coolant goes.

Sputtering could just be the fact that you have changed the vacuum routing to who knows what.

X2

[Timtheguru]

Did you bleed the heater core? One of the hoses has a little hole on it that is used for bleeding. I can't recall the exact procedure for it though.

[ColinBurger00]

I know the hole your talking about, the highest point on the coolant system. I also use the bleeder valve right above the intake manifold.. I have read a zillion procedures and I have no idea which one is most efficient for removing air in the lines?

[Timtheguru]

IIRC the heater core is bled while the car is running, but the bleeder screw/valve next to the intake manifold is bled by just opening it (while the car is off) and filling coolant into the expansion tank until it comes out the screw/valve.

Also, the entire system is self bleeding with enough driving, but the heater core is always a tough one or just takes a long time.

[ColinBurger00]

So someone please explain, my coolant reservoir being pressurized to the point that coolant disappears from it only to return when the cap is loosened, that is an air bubble?

[diagnosticator]

I know the hole your talking about, the highest point on the coolant system. I also use the bleeder valve right above the intake manifold.. I have read a zillion procedures and I have no idea which one is most efficient for removing air in the lines?

Normally, all that is needed is to fill the system, and allow enough time for the added coolant to drain into the system from the tank, while keeping the tank topped up. After the system stops taking coolant from the tank, use the bleeder plug in the coolant pipe above the manifold, and loosen to allow all the air to be pushed out by coolant filling the system. After coolant has filled the pipe at the bleed plug, tighten the plug then top up the expansion tank, then reinstall and tighten the tank cap. Start the engine and run the engine in neutral/Park, at 2000 RPM for 3 minutes. Next, turn the engine OFF, and allow to cool down. After the engine and cooling system is cooled down fully, remove the tank cap and top up the coolant level in the tank if needed. Reinstall the cap and drive the car.

If the cooling system cannot be easily purged of air, and the system continues to experience air in the system symptoms, then there is most likely a coolant leak somewhere, allowing air to get into the system as the coolant cools down after driving.

If there are no leaks in the cooling system, including a faulty head gasket seal, the cooling system is self purging and will circulate any trapped air to the expansion tank, while at the same time, coolant in the expansion tank enters the system circulation to make up for the air purged into the expansion tank.

[Charles.waite]

Cracked block? a cracked head is FAR more likely, and actually sadly common in AMB heads.

[ColinBurger00]

Normally, all that is needed is to fill the system, and allow enough time for the added coolant to drain into the system from the tank, while keeping the tank topped up. After the system stops taking coolant from the tank, use the bleeder plug in the coolant pipe above the manifold, and loosen to allow all the air to be pushed out by coolant filling the system. After coolant has filled the pipe at the bleed plug, tighten the plug then top up the expansion tank, then reinstall and tighten the tank cap. Start the engine and run the engine in neutral/Park, at 2000 RPM for 3 minutes. Next, turn the engine OFF, and allow to cool down. After the engine and cooling system is cooled down fully, remove the tank cap and top up the coolant level in the tank if needed. Reinstall the cap and drive the car.

thank you for that

[diagnosticator]

Cracked block? a cracked head is FAR more likely, and actually sadly common in AMB heads.

I don't know of any confirmed cracked heads, that developed cracks in the cooling jacket walls that are located where coolant can leak into the combustion chambers or intake or exhaust ports. Commonly occurring cracks between the valve seats cannot leak coolant, or leak combustion gasses into the cooling system.

[ColinBurger00]

I don't know of any confirmed cracked heads, that developed cracks in the cooling jacket walls that are located where coolant can leak into the combustion chambers or intake or exhaust ports. Commonly occurring cracks between the valve seats cannot leak coolant, or leak combustion gasses into the cooling system.

I made note of that when I read that in another thread. Its good to know.

[Charles.waite]

I don't know of any confirmed cracked heads, that developed cracks in the cooling jacket walls that are located where coolant can leak into the combustion chambers or intake or exhaust ports. Commonly occurring cracks between the valve seats cannot leak coolant, or leak combustion gasses into the cooling system.

http://www.audizine.com/forum/showth...5-Cracked-head





I thought these cracks in between the valves often resulted in burning coolant int he combustion chamber? Am I mistaken?

Edit: Nevermind, from your own post in that thread Diagnosticator:

The cracks in the webs between the valve seats, are not the cause of the coolant leak into cylinder #2. This is because there are no coolant passages near the webs between the valve seats. This is why the cracks develop in the first place, due to the very high thermal stresses that exist in the webs, as a result of the coolant being so far away as a relative matter. Audi specifies that cracks between the valve seats, do not condemn the head, provided the width of the crack/s is not more than 1mm (0.03937").

Either the head is cracked inside the intake port, (not likely,) or the head gasket was the true source of the coolant leak into cylinder #2. (most likely)

These are the facts of the case, and are not debatable. You can have the head pressure tested, and if there is no pressure lost during the test, then the head can be rebuilt and milled as needed, and reused as long as there are no cracks in the valve seat webs more than 1mm wide. Having already developed, the cracks don't usually get any worse than they are now. IHTHs....

[diagnosticator]

thank you for that

I hope it helps.

One more requirement, when the system is refilled after being drained, the coolant level in the system must be above the level of the coolant pump intake, in order that the pump can circulate coolant without running out of liquid coolant to pump. If the pump does not receive liquid coolant at the pump inlet continuously, then the pump cannot establish coolant flow that is required for the system to self purge air back to the expansion tank. This is why allowing enough time for the coolant added to the tank, to drain down into the cooling system when refilling. It can take awhile for this to happen usually. You just need to watch the tank level and be patient.

If the pump cannot pump steady liquid coolant at start up, then areas in the coolant passages in the block and head will get to hot and produce steam in the system that will make the problem of no circulating coolant even worse. It is prerequisite that the cooling system have enough coolant so that the level in the engine is above the coolant pump intake before the engine is started. Starting the engine after filling the system with the tank cap installed and tightened, helps prevent steam in areas that have an air bubble, that is why the cap should be installed during the start up and run up to 2000 RPM for three min.

If there are leaks in the cooling system, or a failed head gasket, then coolant can leak out and air will enter the cooling system after the car is turned off and cools down. This will eventually result in the cooling system having so much air that the pump does not receive steady liquid coolant at the pump intake, when the engine is subsequently started again.

If the engine shows evidence of initial overheating, and there is no heat from the heater during the initial run up to 2000 RPM, then turn the engine OFF, and allow the engine and coolant to cool down fully before removing the expansion tank cap. Remove the tank cap only after the system has cooled down completely, then top up the coolant level in the tank.

[diagnosticator]

So someone please explain, my coolant reservoir being pressurized to the point that coolant disappears from it only to return when the cap is loosened, that is an air bubble?

This is caused by air trapped in the cooling system expanding as it is heated by the engine, or combustion gasses pressurizing the cooling system from a failed head gasket. The coolant is not circulating properly, not enough liquid coolant at the pump intake, and the coolant in the tank drains into the cooling system, then the pressurized air/gasses in the system pushes the coolant back into the tank when the engine is turned of and or the tank cap is loosened.