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Discussion Starter #1 (Edited)
I know ive been making a lot of threads but i guess that just shows how many problems my car has :frown:

So ive done a bit of research looking around for a similar problem to mine however i cant find one that matches my situation exactly..

Before i begin id like to say that ive already tried replacing my rad cap and thermostat (both OEM) and have no oil-coolant mixtures in my engine or coolant

So here it goes, i have this issue where when i do pulls and hit boost (around 5k peak boost) my rad fills up the overflow tank pretty much all the way to the point where it will literally spray half of the engine bay with coolant.. What follows afterwards varies.

-Either the engine will start to over heat forcing me to crank the heat way up to let it cool
-OR it will remain the operating temp until i drive the car home.

IN EITHER CASE, the rad WILL NOT suck the coolant back in from the overflow tank while the car's running forcing me to take the overflow tank off and empty some of it into a container. the only time it will SOMETIMES DRAIN is when the car's off (when i leave it overnight). In the event that it does decide to drain back into the rad, its usually completely empty next morning.

a weird thing to note is that if i drive the car normally, NONE of this happens. the overflow fills properly to the right amount and drains properly.

Another thing I did was I took off the rad cap and revved up the motor to around 3k and coolant started overflowing from the rad, I don’t know if that’s normal though.

Ive had my tuner say its a head gasket issue but it just doesnt make sense to me.. what do you guys think?
 

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Blown head gasket ia most likely caused by preignition due to too much timing. I would talk with tuner who did tuning if he can pull out some timing.
What's your hp numbers and boost pressure?
 

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That's a lot of power!

Do the cooling fan(s) turn on and off correctly? If not, fix this first. If they do work correctly, continue reading.

The radiator neck can smell like raw fuel OR a rich combustion gas mixture if combustion gases are entering the cooling system. If the radiator under the cap smells like your tail pipe does when your engine is idling, you have combustion gas blow-by. Your radiator should only ever smell like a rather fresh bottle of coolant (smell this for a comparison). Gases can enter the cooling system due to blown head gasket, cracked cylinder wall(s) or cracked head (rare on these engines).

Start the car and smell the tail pipe as a sample to compare against. Then smell the radiator neck opening. If it smells the same, it's combustion gas blow-by coming from one of the two above mentioned gas sources. Either way, you have to pull the head to verify.

Another way to test this, you need a cooling system pressure tester. This device attaches to your radiator where the radiator cap goes, and it is a small air pump with a gauge on the end of it. It allows you to pump air into the cooling system to check for leaks, as well as monitor cooling system pressures. Two ways you can check for blow-by using this tool:


1. Pull the spark plugs from all cylinders. Turn crankshaft so that all 4 pistons are in the middle of the cylinders. Use the tool to apply 15-17PSI air pressure to the cooling system. Check for any immediate leaks while the system is under pressure. Use a flashlight and inspect the insides of the cylinders. If the leak is bad enough, you will see coolant dripping into the cylinders rather quickly. If you don't see coolant right away, let the car sit with the applied pressure in the cooling system overnight. Come back in the morning and reinspect the cylinders for coolant. If there is a leak, pull the head and find out what's wrong.


2. Let the car cool down completely. Attach this tool to the radiator. Do NOT apply pressure to the cooling system using the air pump mechanism. Start the car and read the gauge right away. Pressure should NOT build right away at a fast pace. If it does, pull the head. If pressure does not build quickly after initially starting, grab a helper. Watch the pressure gauge on the tool and have a friend do a quick throttle snap. Make sure the turbo builds some boost pressure under the throttle snap. If the cooling system builds pressure quickly and the pressure STAYS (does not lower back to where it started + or - 1 to 2 PSI), most likely combustion gas is blowing into the cooling system. Watch the gauge, and if doing quick throttle snaps allows the cooling system to build pressure ABOVE 20PSI, something is definitely cracked/blown. If this happens, shut the engine off before your radiator explodes!


Quick throttle snaps should not allow a properly functioning cooling system to reach high system pressures (15-18PSI) in times under a minute when starting from ambient cooled down coolant temperatures. The engine itself physically cannot get water to boil in that short period of time, especially under no-load conditions.

Use this knowledge when going into this type of testing. If you see pressures rising stupid fast from cold, something is wrong and head will need to be pulled for inspection.

From the way you describe your symptoms, it definitely sounds like combustion gas blow-by and the head will be coming off in the very near future. If you DO decide to pull the head for this type of symptom, ALWAYS get a machine shop to magnaflux the head and inspect for cracks. Get them to check to make sure the head is not warped, as it may be. Do NOT simply throw a new head gasket in place after experiencing these symptoms. Inspect and measure EVERYTHING you can before reinstalling. Installing a new head gasket to a warped head/block surface is just asking for it to blow out again, likewise a cracked block or head will end up having the same symptoms and you just did all that work for nothing.



Edit: I use the term "magnaflux" to refer to the tool sets created to test all metals for cracks, ferrous or not. Aluminum can still be checked for cracks, just not using the magnaflux tooling. ALWAYS get this procedure done when building engines, check all high stress components for cracks. It usually only costs an extra $100 bucks at the machine shop to have the block, head and crankshaft checked. I can just hear someone out there saying "Ya can't magnaflux aluminum!" lol.
 

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drtalon123, you must be kidding, right? You know that applying 19 psi through spark plug holes will give you nothing. It is nearly nothing what combustion chamber see. Also Honda head micro crack possibility is near to nothing or one to ten thousand.

Just change your gasket, do not forget to resurface head and pull out some timing.
 

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drtalon123, you must be kidding, right? You know that applying 19 psi through spark plug holes will give you nothing. It is nearly nothing what combustion chamber see. Also Honda head micro crack possibility is near to nothing or one to ten thousand.

Just change your gasket, do not forget to resurface head and pull out some timing.

Not through the spark plug holes lmao, through the radiator neck! Letting the car cool down, pressurize the cooling system to slightly above normal pressures, pull the plugs and watch. This is a very common way of checking for a cracked block/head/blown head gasket. It should be an effective check especially if the OP is describing symptoms such as blowing coolant from the overflow tank all over his engine under WOT.

If nothing happens with the plug-out method, then do it the other way suggested with the throttle snap reading the gauge on the end. Either way he should find something.

There is a 3rd method if you have access to a 5 gas analyzer, but most folks or shops don't so I'll leave that one alone.
 

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And what's the difference checking it through rad neck vs spark plug hole? Direction does not matter in any way there. It is not blown cardboard head gasket where you can possibly check it this way. Also cracked head would cause problems right after reaching engine operation temperature.
Topic author already described coolant overflow only under turbo pressure. Save his time and money... let him change head gasket and problem solved.
 

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Discussion Starter #13
And what's the difference checking it through rad neck vs spark plug hole? Direction does not matter in any way there. It is not blown cardboard head gasket where you can possibly check it this way. Also cracked head would cause problems right after reaching engine operation temperature.
Topic author already described coolant overflow only under turbo pressure. Save his time and money... let him change head gasket and problem solved.
I hope there isn’t anything cracked 😫 the last thing I need is to go out looking for a z6 block that’s already hard to find...
 

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That's a lot of power!

Do the cooling fan(s) turn on and off correctly? If not, fix this first. If they do work correctly, continue reading.

The radiator neck can smell like raw fuel OR a rich combustion gas mixture if combustion gases are entering the cooling system. If the radiator under the cap smells like your tail pipe does when your engine is idling, you have combustion gas blow-by. Your radiator should only ever smell like a rather fresh bottle of coolant (smell this for a comparison). Gases can enter the cooling system due to blown head gasket, cracked cylinder wall(s) or cracked head (rare on these engines).

Start the car and smell the tail pipe as a sample to compare against. Then smell the radiator neck opening. If it smells the same, it's combustion gas blow-by coming from one of the two above mentioned gas sources. Either way, you have to pull the head to verify.

Another way to test this, you need a cooling system pressure tester. This device attaches to your radiator where the radiator cap goes, and it is a small air pump with a gauge on the end of it. It allows you to pump air into the cooling system to check for leaks, as well as monitor cooling system pressures. Two ways you can check for blow-by using this tool:


1. Pull the spark plugs from all cylinders. Turn crankshaft so that all 4 pistons are in the middle of the cylinders. Use the tool to apply 15-17PSI air pressure to the cooling system. Check for any immediate leaks while the system is under pressure. Use a flashlight and inspect the insides of the cylinders. If the leak is bad enough, you will see coolant dripping into the cylinders rather quickly. If you don't see coolant right away, let the car sit with the applied pressure in the cooling system overnight. Come back in the morning and reinspect the cylinders for coolant. If there is a leak, pull the head and find out what's wrong.


2. Let the car cool down completely. Attach this tool to the radiator. Do NOT apply pressure to the cooling system using the air pump mechanism. Start the car and read the gauge right away. Pressure should NOT build right away at a fast pace. If it does, pull the head. If pressure does not build quickly after initially starting, grab a helper. Watch the pressure gauge on the tool and have a friend do a quick throttle snap. Make sure the turbo builds some boost pressure under the throttle snap. If the cooling system builds pressure quickly and the pressure STAYS (does not lower back to where it started + or - 1 to 2 PSI), most likely combustion gas is blowing into the cooling system. Watch the gauge, and if doing quick throttle snaps allows the cooling system to build pressure ABOVE 20PSI, something is definitely cracked/blown. If this happens, shut the engine off before your radiator explodes!


Quick throttle snaps should not allow a properly functioning cooling system to reach high system pressures (15-18PSI) in times under a minute when starting from ambient cooled down coolant temperatures. The engine itself physically cannot get water to boil in that short period of time, especially under no-load conditions.

Use this knowledge when going into this type of testing. If you see pressures rising stupid fast from cold, something is wrong and head will need to be pulled for inspection.

From the way you describe your symptoms, it definitely sounds like combustion gas blow-by and the head will be coming off in the very near future. If you DO decide to pull the head for this type of symptom, ALWAYS get a machine shop to magnaflux the head and inspect for cracks. Get them to check to make sure the head is not warped, as it may be. Do NOT simply throw a new head gasket in place after experiencing these symptoms. Inspect and measure EVERYTHING you can before reinstalling. Installing a new head gasket to a warped head/block surface is just asking for it to blow out again, likewise a cracked block or head will end up having the same symptoms and you just did all that work for nothing.



Edit: I use the term "magnaflux" to refer to the tool sets created to test all metals for cracks, ferrous or not. Aluminum can still be checked for cracks, just not using the magnaflux tooling. ALWAYS get this procedure done when building engines, check all high stress components for cracks. It usually only costs an extra $100 bucks at the machine shop to have the block, head and crankshaft checked. I can just hear someone out there saying "Ya can't magnaflux aluminum!" lol.
So out of the tests you mentioned, I was only able to do one before work today 😕. I let the car reach operating temp and the rad doesn’t have any odor of gas or exhaust in it, I’ve compared it to a coolant bottle as you mentioned and they both smell exactly the same. Does this mean it could be something else?
 

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And what's the difference checking it through rad neck vs spark plug hole? Direction does not matter in any way there. It is not blown cardboard head gasket where you can possibly check it this way. Also cracked head would cause problems right after reaching engine operation temperature.
Topic author already described coolant overflow only under turbo pressure. Save his time and money... let him change head gasket and problem solved.

Dude, this is seriously an actual way to check for head gasket leakage. You never want to assume it's only a head gasket. With his power levels if the cylinder sleeves are stock one of them could be cracked. You want to do it through the rad neck, NOT the spark plug holes for two reasons:


1. Doing it through the cylinders won't work, the pressure will simply blow by the piston rings really fast. The cooling system is designed to sustain low pressures over long periods of time during engine operation. The cooling system is a much better place to apply pressure, as you can verify external coolant leaks and repair them quickly to help sustain pressure.


2. When you pull the plugs, pressurize the cooling system slightly above normal operating pressures (around 19-20PSI), and let it SIT for 12+ hours, if the leak is present and severe enough, you can look in the cylinder with a flashlight and see actual coolant puddling up on top of the piston nearest the leakage.

It takes a while, which is why actual shops usually set this up on a car BEFORE they leave the shop for the night. When they come in at start of shift next morning, they can look in the cylinders and check for small amounts of puddling.

It's not going to fill the cylinder very fast if the crack is tiny or the head gasket leak is small, but from the way the OP describes it under boost, the combustion chamber seal somewhere is severely compromised. That should be detectable using the method I described, it just takes some time. The coolant will very slowly work it's way past the leak and into the cylinder if it is a bad enough leak (OP's description suggests that it is).

Doing it this way actually tells you the closest location of the leak, allowing you to inspect THAT cylinder area for any possible block/head cracks really well before just assuming it's the head gasket. Automotive repair shops usually do not like to assume it's only the head gasket because it WILL come back and bite you in the ass if you don't check for cracks (the one time you don't is usually the one time you wish you did).




Occasionally, the head gasket leak is very small and this method does not work. In this case, you will need to get your cylinder pressures raised in order for combustion gases to push their way past the seal failure point to watch for increased cooling system pressure OR the presence of unburned hydrocarbons.

The only reason I recommended what I wrote, is because I would rather spend the time diagnosing it correctly and accounting for most all possibilities before putting in the time required to R&R the head. This way, you have a better idea of what to expect during tear down and not assume anything. It's not backbreaking work performing these tests either, most of it is just watching and seeing what you get.

I'm not wasting his money if he does what I suggested himself. All that is required is a radiator pressure tester which costs $30 bucks at Princess Auto/Harbor Freight OR borrow one from a technician friend (I would loan you mine if you were closer lol) and an hour or so performing the tests that can be done WITHOUT this tool first, then overnight to perform the in-cylinder leak check with the tool. Other than the tool, these are all free and he will be more confident in which component to inspect/repair/replace.

I do not endorse the shotgun parts replacement method, it has pissed off way too many customers of fellow technicians who rely on this method too often. I 100% endorse proper diagnostics to determine most likely root cause first.
 

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I hope there isn’t anything cracked �� the last thing I need is to go out looking for a z6 block that’s already hard to find...

It sucks you have these symptoms, I have just seen too many times where it's not just simply the head gasket. I would hate for you to pull the head, get it only resurfaced and not checked for cracks, not check the block/liners for cracks and get it all back together with a new head gasket only to have the same issue. Perform the tests I suggested, and you will be more confident in what to look for when you tear the engine down.

If one of the leakage tests I suggested fail, the only way to see what you've got is to pull the head. At least you have done the testing to verify that you do indeed have a leak, and hopefully you can use the in-cylinder leak check to determine the cylinder closest to the leak so you can make a thorough inspection of that area.

Let us know what you come up with!
 

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So out of the tests you mentioned, I was only able to do one before work today 😕. I let the car reach operating temp and the rad doesn’t have any odor of gas or exhaust in it, I’ve compared it to a coolant bottle as you mentioned and they both smell exactly the same. Does this mean it could be something else?

Perform the other test with the wide open throttle snap. It can be done (by feel only) without using the pressure testing tool on the radiator neck. See below (Make sure to perform this test ENGINE COLD, in UNDER 1 minute of total run time):

1. Let the car cool all the way down. Fill the cooling system to the top, and bleed as necessary to get most of the air out of the system. Close the radiator cap.

2. Use a friend to start the engine and snap the throttle hitting boost. At the SAME TIME he is snapping the throttle open, squeeze the upper radiator hose HARD with your strongest hand.

3. Get him to snap the throttle hitting boost a few times. If the head gasket/block/head is cracked/leaking and combustion gases are entering the cooling system, the radiator hose will inflate and become HARD to the point where you can't squeeze it flat anymore.

4. You should notice that each time he revs the engine high, the radiator hose inflates more than the previous time. MAKE SURE that the pressure RISES and then HOLDS.


Two things to look out for doing this method:

1. The water pump CAN build pressure during high RPM operation, but as soon as the RPMs fall the pressure should subside in a properly operating cooling system.

2. If the pressure BUILDS and HOLDS and does NOT subside, pressure is only moving one way and this usually indicates pressure being built in the system ABOVE and BEYOND what can be noticed through thermal coolant liquid expansion.


Use your best guess, hopefully you have felt what a radiator hose normally feels like on an engine up to normal operating temperature. From this, you should be able to use this experience to determine if your car is normal or not.


Again, let us know what you come up with! I apologize for the lengthy posts, but I'm trying to cram in as much of my experience as I can without leaving any important details out.
 

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Given the circumstances you've described, it does seem like the HG is the likely culprit.

If you have a MLS gasket installed currently and you didn't severely overheat the engine, you may be able to get by with just replacing the HG without worrying about decking/milling.

In regards to the tune, I would strongly suggest that you determine whether or not there's detonation occurring. If it was detonation that caused the issue, you'll see it reoccur or worse (cracked ringlands/melted piston). You can build a det can for cheap and listen for yourself before (or after) you replace the HG.

You can also pull the spark plugs and look for obvious signs of detonation. You can google images of plugs that show detonation/pre-ignition.

I wouldn't blindly go to your tuner and ask for timing to be pulled if the tune was good to begin with.

I assume you're using properly torqued ARP head studs?
 

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You have done simple things you could do to check if you cang get around taking off the cylinder head. You can waste your time and perform 100 more useless tests. We are talking about d-series head which takes only few hours head gasket to be changed. It's fast, easy and cheap. Issue you are looking for can be seen/found under cylinder head. So what are you waiting for? It won't fix itself...
 

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I do work with engine heads every day as a mechanic at engine repair shop. Pressurizing coolant system the way you described is inaccurate way to test micro cracks. We check a lot of heads every day and most of cracks only open at engine operating temperature.
Changing d-series gasket will take less time and money than performing useless tests. Problem will be seen with bare eye when head will be pulled off either it's gasket (most likely) or cylinder crack (99% it's not).
 
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