Let's talk about cylinder head cracking!

olypopper · **Posted:** Wed Sep 18, 2019 12:05 pm

Mine developed a slow coolant leak/usage problem about 1 year ago...........seemed to come and go with no rhyme or reason. With the arrival of summer in Alaska this year, I noticed the little jeep would leave an impressive trail of smoke while climbing out of my driveway and the smoke lingered much longer than your normal condensation/exhaust. Further inspection revealed an increase in coolant disappearing. This engine had the head gasket replaced and head studs installed at 117k and it's now got 138k. Had lot's of other goodies thrown at it too.........like GDE hot tune, HDS001 Tstat, etc. I was worried about the potentials like cracked block, liner problem's etc but had no co-mingling of coolant and oil or external leaks so I decided to rip the head off and have it checked.

The head gasket was beautiful with excellent clamping witness marks in the head and block. What I found was a drop of coolant hanging on the #2 glow plug tip. My machine shop pressure up the head and much to my chagrin, found no cracks! I went back to the drawing board and inspected and reinspected. I couldn't find anything wrong. At this point, I asked my local machine shop to heat the head up and re-test. This time, they found the crack. The crack was under the exhaust valve seat on the #2 cylinder. Seems to be some pretty thin meat there. Is this the most common cracking spot on these heads?

I purchased a new one from Seth at Sasquatch and have installed it already and she's running great again.

olypopper · **Posted:** Wed Sep 18, 2019 12:18 pm

Let me know if this link works:

https://drive.google.com/open?id=1ytrxH ... QjY9h510_8

https://drive.google.com/open?id=1klCAF ... U_pZp3thTb

65Corvair · **Posted:** Wed Sep 18, 2019 1:16 pm

I have a similar situation with mine as well, my jeep was using coolant, I replaced my head gasket and used ARP studs, but it still uses coolant. I feel my cylinder head has a crack, I need to do a pressure test to verify though.

Sent from my Pixel using Tapatalk

Mountainman · **Posted:** Wed Sep 18, 2019 3:00 pm

Almost always a tiny leak from the factory hose clamps on the turbo side of the engine (assuming you EGR is gone). The bottom of the reservoir is the usual culprit, but sometimes it's coming from where the thermostat mates to the head.
Get the engine hot, rev it up to 2500 or so for 10 seconds or so, and then touch your finger to where each of the hoses connect, and look at your finger immediately. you will get burnt a little, latex glove helps, but that's I find them quickly. I pinch my finger down on the bottom of the hose (where it connects) as to access the slightest seep.

After overheating one engine repeatedly with different cooling setup experiments with heavy towing, I managed to crack a head inbetween two valves.
- multiple oil starved and thereby overheated engines with no cracks. But like the blocks, there have been a few reported on lost, just rare. :2cents:

TKB4 · **Posted:** Wed Sep 18, 2019 5:22 pm

Flash and about 3 others I have read about on lost.
I guess morale of the story is if you remove head because of any loss of coolant issue get it checked and now ,maybe checked warm and hot ,don't just replace head gasket alone assuming it is the source

flash7210 · **Posted:** Wed Sep 18, 2019 6:02 pm

Speak of the devil... :twisted:

I experienced my cracked head at 160k miles.
I initially diagnosed it as a bad head gasket.
Pulled the head, had local engine shop clean it and check for cracks, and I put it back on.
Same symptoms. Loss of coolant and huge plumes of white smoke out the exhaust.

So I did my own pressure test to check for a cracked head.
Right away confirmed cracks at cylinders 2 and 3.
Later confirmed #4 also.
All the cracks were at the exhaust valve seats.

GordnadoCRD · **Posted:** Wed Sep 18, 2019 6:29 pm

Flash, I've never asked before, but always assumed..

Your replacement head, with no other changes, has had no further problems...?

This leads me to believe that the problem is inconsistent manufacturing process, or materials...?

(assuming no changes in the way you drive.)

?

flash7210 · **Posted:** Wed Sep 18, 2019 6:46 pm

GordnadoCRD wrote:

Flash, I've never asked before, but always assumed..
Your replacement head, with no other changes, has had no further problems...?
This leads me to believe that the problem is inconsistent manufacturing process, or materials...?
(assuming no changes in the way you drive.)
?

I’ve got roughly 70,000 miles on my replacement head. No issues.
If anything, I’m rougher with it now than before. I don’t baby it anymore.
Head was a used part from VMspecialits, unknown mileage or history.
It has a 2007 date code.
My cracked head had a 2004 date code.

Tried to conduct a survey of others with cracked heads.
Few responded. So can’t really confirm if 2004 heads are worse than others.

flash7210 · **Posted:** Wed Sep 18, 2019 7:17 pm

The head cracks the way it does because of heat.

Hot exhaust valve closes, transferring its heat to the hardened valve seat, then to the aluminum, and finally to the water jacket.
If there is not enough coolant flow around the exhaust valve areas, or if steam pockets form in the water jacket, these areas will become heat stressed and crack.
And it is possible to have small localized steam pockets without any indication of overheating or rise in temperature.

In my case, I am convinced that the cause was because of poor coolant flow due to my choice of using a in-line thermostat in conjunction with a failed factory thermostat. Where the factory thermostat was opening too early, blocking the bypass outlet, and the in-line remained closed and blocked all coolant flow for a short period of time.

But if the OP was using the HDS thermostat then that might throw my theory out the window. (Although I still stand by it)

Still, casting flaws and poor design are possibilities too.
But the root cause is heat. (Same for broken exhaust valves)

So, create a free flowing exhaust to allow all that heat to escape quickly.
And let your engine run as cool as comfortably possible. A 195 thermostat might be too hot.
I’ve used both a 160 and a 180 thermostat with no ill effects.

layback40 · **Posted:** Wed Sep 18, 2019 8:02 pm

I experienced a similar problem a few years ago with my XJ. Its an export one with the VM 425 engine. They have separate heads for each cylinder. I obtained a set of second hand heads & when pressure tested, one had a leak under one of the inlet valve seats. Took the seat out & it looked like a casting imperfection, not a crack. Ground back with a die grinder & followed the imperfection for many mm until it reached the cooling jacket. Thought about welding it back together but never bothered.

Mountainman · **Posted:** Wed Sep 18, 2019 9:45 pm

X2 on the inline thermostat (my jeep had one when I bought it, clamshell style with a regular thermostat). 2005 cast date. Between exhaust valves.

I've had over a dozen tested by machine shop, no leaks yet except the one I abused. I think 50% or more of the ones reported on lost had inline stats...

These days you want to swap your exhaust valves out anyhow, so a cracked head might give you an opportunity to save your engine :dizzy:

GordnadoCRD · **Posted:** Wed Sep 18, 2019 11:06 pm

flash7210 wrote:

The head cracks the way it does because of heat.

Hot exhaust valve closes, transferring its heat to the hardened valve seat, then to the aluminum, and finally to the water jacket.
If there is not enough coolant flow around the exhaust valve areas, or if steam pockets form in the water jacket, these areas will become heat stressed and crack.
And it is possible to have small localized steam pockets without any indication of overheating or rise in temperature.

In my case, I am convinced that the cause was because of poor coolant flow due to my choice of using a in-line thermostat in conjunction with a failed factory thermostat. Where the factory thermostat was opening too early, blocking the bypass outlet, and the in-line remained closed and blocked all coolant flow for a short period of time.

But if the OP was using the HDS thermostat then that might throw my theory out the window. (Although I still stand by it)

Still, casting flaws and poor design are possibilities too.
But the root cause is heat. (Same for broken exhaust valves)

So, create a free flowing exhaust to allow all that heat to escape quickly.
And let your engine run as cool as comfortably possible. A 195 thermostat might be too hot.
I’ve used both a 160 and a 180 thermostat with no ill effects.

Your explanation is possible to the point of probable, but it caused another possible scenario to excite old experiences. (Volkswagen)
Hang with me here..
Volkswagen's early 1.5L Diesels were hugely successful except for head gasket failures which they solved with modified head bolts. They were gutless, but popular with the mid-1970s people seeking high fuel economy.
They experimented with turbocharging the 1.5L D, but never brought it to market due to nearly 100% failure rate, and it took them a long time to discover the fault.
All of the VW water cooled engines of that era, both Diesel and petrol had essentially identical iron block/aluminum head format, that worked suitably for all their naturally aspirated engines.
The problem with the turbodiesel, was the high temperature differential between the combustion temperature inside the precombustion chamber, and the coolant on the far side the aluminum head that contains it. The metals used were not capable of processing that much temperature gradient (BTU) without failure.
Since they had to go back to the drawing board to fix this, they changed the metallurgy of the whole engine. With the 1.6L diesel, they used the existing block and aluminum head but upgraded the precombustion chambers to a special hard steel (stellite?)
In the turbodiesel they added a special high silicon alloy aluminum head that could survive the super high temperature gradient the turbo diesel produced. They also enlarged the precup volume lowering the compression ratio from 26:1 to 24:1 This also lowered combustion temperature. Additional differences were a forged crankshaft, forged rods, forged pistons of special high silicon alloy aluminum. (which were not available aftermarket, and the OEM price was $400 each) Even the block was made of a different alloy from all their other engines, and had oil cooling for the pistons virtually identical to the CRD, all to deal with high combustion temperatures.
This is where it comes back to your heat-pathway example.
It's not so much the combustion temperature, but the exhaust temperature as it passes through the valves with gasses still burning. Many things influence this. Higher compression ratios tend to speed up combustion and lower exhaust temperatures. Fuel type does as well. Higher cetane content speeds vaporization and flame speed. INjector nozzle condition helps with consistent fuel particle size. All other things equal, Increasing injection pressure reduces fuel particle size, which speeds vaporization=more complete pre-exhaust combustion.
Basically since we don't have any control over VM Head alloy, reducing exhaust temperature differential by whatever means, is the best bet to help avoid splits and coolant leaks.

olypopper · **Posted:** Thu Sep 19, 2019 11:48 am

I have a much simpler theory as to why these heads crack under the seat. I believe the casting is too thin in the area of the seat and after machining, the wall thickness into the water jacket is prone to failure after many thermal cycles. I cut my head open with a band saw and inspected and was surprised how thin that area was. I did not take pictures before I tossed the head but if someone else feels like cutting one open, please post the pictures.

flash7210 · **Posted:** Thu Sep 19, 2019 12:14 pm

olypopper wrote:

I have a much simpler theory as to why these heads crack under the seat. I believe the casting is too thin in the area of the seat and after machining, the wall thickness into the water jacket is prone to failure after many thermal cycles. I cut my head open with a band saw and inspected and was surprised how thin that area was. I did not take pictures before I tossed the head but if someone else feels like cutting one open, please post the pictures.

It would be nice if we could identify a production time frame where these heads might be prone to cracks.

It certainly could be in the way the head is cast.
But what is too thin?
What could we compare to?
Duramax heads are aluminum. Is that a good comparison?
I don’t have any data to make a comparison.

In any case, it’s heat. As in high exhaust temps.
Whether it be a broken exhaust valve or a cracked head.
I’d rather deal with a cracked head than a broken valve.
But they both suck to have happen.

WWDiesel · **Posted:** Thu Sep 19, 2019 2:49 pm

flash7210 wrote:

In any case, it’s heat. As in high exhaust temps.

Very true!
Too thin of a cast may well contribute to head cracking, but at the end of the day just as Flash said, Ultimately it is HEAT, i.e. high combustion chamber and exhaust gas temperatures along with thermal cycling fatigue that can cause cracked heads and exhaust valve stems to suddenly break off.

So as a CRD owner, anything you can do to help lower or limit exhaust combustion temperatures is a very worthwhile endeavor for engine longevity.
Some things that can help lower combustion exhaust temperatures (EGT's)
1. Higher boost pressures during engine loading; this can include good VV turbo vane operation / controls, good quality boost hoses, no FCV or flapper, and clean CAC (intercooler)
2. Good fuel control; no overfueling. engine ECM tuning.
3. Non-restrictive exhaust system;includes no CAT and free flowing muffler like a Flow Master.
4. Least restrictive air intake system. (Clean air filter)
5. Good coolant system operation and control (thermostat) NO in hose or inline type thermostat!

CGman · **Posted:** Thu Sep 19, 2019 7:38 pm

WWDiesel wrote:

flash7210 wrote:

In any case, it’s heat. As in high exhaust temps.

Very true!
Too thin of a cast may well contribute to head cracking, but at the end of the day just as Flash said, Ultimately it is HEAT, i.e. high combustion chamber and exhaust gas temperatures along with thermal cycling fatigue that can cause cracked heads and exhaust valve stems to suddenly break off.

So as a CRD owner, anything you can do to help lower or limit exhaust combustion temperatures is a very worthwhile endeavor for engine longevity.
Some things that can help lower combustion exhaust temperatures (EGT's)
1. Higher boost pressures during engine loading; this can include good VV turbo vane operation / controls, good quality boost hoses, no FCV or flapper, and clean CAC (intercooler)
2. Good fuel control; no overfueling. engine ECM tuning.
3. Non-restrictive exhaust system;includes no CAT and free flowing muffler like a Flow Master.
4. Least restrictive air intake system. (Clean air filter)
5. Good coolant system operation and control (thermostat) NO in hose or inline type thermostat!

Which still leaves the elephant in the room... what kind of EGT info do we have on STD tune vs ECO tune vs HOT tune vs YETI tunes, and is this part of the problem.

WWDiesel · **Posted:** Thu Sep 19, 2019 10:37 pm

CGman wrote:

Which still leaves the elephant in the room... what kind of EGT info do we have on STD tune vs ECO tune vs HOT tune vs YETI tunes, and is this part of the problem.

Yes, wish we had the data! (numbers)
Any sustained (key work) EGT's coming out of the head pre Turbo 1200 degrees F or greater can be very detrimental to the head, the exhaust valves, and the pistons.
Best to keep the EGT's below the 1200 degrees threshold.

Anything that can prevent or severely limit coolant flow (like an inhose thermostat) through the aluminum head during the critical warmup period that can cause steam pockets and hot spots can be real detrimental to the head and / or the exhaust valves.

TURBO-DIESEL-FREAK · **Joined:** Sat Apr 17, 2010 3:29 pm **Posts:** 1167

flash7210 wrote:

The head cracks the way it does because of heat.

Hot exhaust valve closes, transferring its heat to the hardened valve seat, then to the aluminum, and finally to the water jacket.
If there is not enough coolant flow around the exhaust valve areas, or if steam pockets form in the water jacket, these areas will become heat stressed and crack.
And it is possible to have small localized steam pockets without any indication of overheating or rise in temperature.

In my case, I am convinced that the cause was because of poor coolant flow due to my choice of using a in-line thermostat in conjunction with a failed factory thermostat. Where the factory thermostat was opening too early, blocking the bypass outlet, and the in-line remained closed and blocked all coolant flow for a short period of time.

But if the OP was using the HDS thermostat then that might throw my theory out the window. (Although I still stand by it)

Still, casting flaws and poor design are possibilities too.
But the root cause is heat. (Same for broken exhaust valves)

So, create a free flowing exhaust to allow all that heat to escape quickly.
And let your engine run as cool as comfortably possible. A 195 thermostat might be too hot.
I’ve used both a 160 and a 180 thermostat with no ill effects.

Aluminum head/iron block engine architecture is relegated to being used in consumer grade passenger vehicle and perhaps boating applications. The commercial trucking industry, the military, and people involved in commercial water transportation would not stand for the headaches caused by two differing metals expanding at two different rates... it is iron head/iron block architecture only with the camshafts being driven by gears, (as it should be for everyone!).

What we have with the V.M. Motori line of automobile engines are what I call "delicate" engineering. The issues that come into play regarding the differences in thermal expansion of the cylinder head vs. the block are only partially solved by things like torque-to-yield bolts. It is much more problematic to make modifications to engines like these than traditional diesel engines without running into consequences. As such, when modifications like the ill-advised inline thermostat are employed, a lot of bad outcomes can be expected.

The HDS Model 001 will not cure the problem of delicate engineering in the R425 and R428 engines, but it will allow you to raise engine operating temperatures safely because it makes no changes to how the cooling system functions. In other words, it will not make the situation any worse; this is something that can not be said of the inline thermostat solution.

What these engines really need are cylinder head upgrade replacements made of IRON.

GordnadoCRD · **Posted:** Fri Sep 20, 2019 9:54 pm

What I'm trying to point out, is that we've fallen into the aluminum=aluminum thought trap.

It's not so much the heat as the heat gradient that's killing these.
Similar to an electric wire. As the voltage differential increases, the copper heats up, until there is so much current, that it simply destroys the metal.

It's too much heat gradient for this particular material VMM is using. The differential between the exhaust valve seats, and the coolant passages, is not up to the BTU load,(comparable to AMPS in elecricity), so it heats up and cracks due to the difference in molecular movement from one side to the other.

Aluminum comes in hundreds of alloys that change it's properties immensely. It's not just cast vs billet, or automotive vs aircraft grade either.
Some manufacturers (Ferrari comes to mind) that even have their own proprietary alloys that they've developed and do all their own in-house castings and forged billets from which they machine in-house as well.

Since we're not in a place to make our own heads (at least I'm not) out of a better material, the only things we can do to decrease this thermal current gradient is tune them back to the original F37 OEM tune, OR, increase the operating coolant temperature, which brings a mixed bag of tricks, and while it will decease the thermal gradient, I have no idea how much is necessary / enough.

turblediesel · **Posted:** Sat Sep 21, 2019 4:58 am

An Italian mechanic told me alloy engines need a good warmup before they're driven. Without warmup microfractures happen within the parts and eventually the part fails. The problem is that one end of a part gets too hot compared to the other end. He was showing me an alloy rod cap from a Juno designed 2.0L Alfa Romeo engine a friend had blown up.

Valves get rid of most of their heat to the valve seat and on to the head and coolant. Get in and go fast with a cold engine and make cracks around the valve seats and something's going to break.

I worked on lots of overheated Fiats with iron blocks and aluminum heads. They usually warped the heads but didn't drop valves. Olypopper mentioned there isn't much material in our heads surrounding the valve seats which probably makes them more vulnerable.

Warm it up until the head is the same temp everywhere and then romp on it.

Let's talk about cylinder head cracking!

Who is online