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Coolant leak inbetween head and block. - mechanixrds - 04-05-2026
Hey there guys, I am new to this forum but I have been coming to this site for information for quite some time now. I am currently working on a demandated cm871 ISX 15 that I rebuilt last October. The truck came back with just under 15,000 miles after the rebuild. As I've read on here before, and also frowned upon, aftermarket parts were used when rebuilding this engine. I used a {after-garbage} inframe kit and DCW aftermarket cylinder head. Counterbores were also addressed at that time. The truck came back for coolant in the exhaust and after further inspection I found that we had coolant coming out of #1 cylinder. I then proceeded to remove the injector and use my borescope to inspect. You can clearly see it leaking from the head and also appears to be leaking from the cylinder walls. No coolant was seen leaking from the bottom end of the motor after the pan was removed. Liner protrusion was checked after the failed cylinder head was removed and was in spec according to the service manual. I will be posting pictures and measurement spec later. A new cylinder head was installed and then put back together. As I was finishing filling it up with coolant, I noticed that I had a coolant leak on the front right side of the engine in-between the cylinder head and the block. To make a long story short, I pulled the engine and sent the block to the machine shop and had it checked out. The machine shop did not find anything wrong with the block. We did have the deck resurfaced and the counterbores reset. After the machine work, I did end up replacing two liners because I wasn't happy with the liner protrusion. Once that was satisfactory, I then proceeded with putting it back together. I installed the cylinder head and torqued it to 300 ft/lbs and let it sit overnight before applying the final 90 degrees. The final torque was done by hand instead of using an impact. After the cylinder head was torqued, I decided to pressure up the cooling system to make sure it wasn't leaking. Unfortunately, it is still leaking in the same spot.
At this point, I have checked all the head bolts(OEM) free length and used a straight edge to check the new cylinder head for any warpage. I'm at a loss for words as I can't seem to figure out why it is leaking after the block got machined. Has anyone else on here experienced this problem before? And if so, what was the cause and how was it rectified? [attachment=10249][attachment=10250][attachment=10251][attachment=10252]
I have videos but couldn't upload them due to the format. I can share them to anyone who would like to see them via a google drive link.
RE: Coolant leak inbetween head and block. - Nostalgic - 04-05-2026
Once you get to the "deck a block" stage, throw it away.
Get a new block. OE Parts.
That said, I know you won't do that. You state the head was checked for flatness, and the deck - that only leaves the gasket.
RE: Coolant leak inbetween head and block. - mechanixrds - 04-05-2026
I've gone through two head gaskets at this point. One with the new head and un-machined block and the second with the same new head and machined block. Same results both times. I've thought about putting on a new OE gasket but, to be honest, I don't want to take that gamble and be in the same position as this is a warranty job.
Here are the links to the videos:
Original failure
{video links removed.. they do not work.}
After block machine work with cooling system under pressure.
{video links removed.. they do not work.}
Both times with a new gasket.
Curious, why do you say to throw away the block if it has to be decked?
As far as aftermarket parts go, I've used a particular brand of in-frame kits, cylinder heads, and other components for close to a decade now and have never had any issues with them until about six months ago.
RE: Coolant leak inbetween head and block. - Nostalgic - 04-05-2026
I ran a decked block. You wouldn't think it would be enough to affect compression ratio and FCA, but it does. Not to mention alignment of your front gear train. I did the exact same thing as countless other guys - ignored Rawze and continued to try to make it right, doing it "my way". Spoiler, eating crow is unpleasant, not to mention expensive.
I can't see your videos. Only other thing I can think of, sans gasket being cause, is make sure your dowel holes are aligned correctly and the dowels actually fit in them and allow head to fully seat. I've heard of machining on aftermarket heads being off enough to cause issues.
RE: Coolant leak inbetween head and block. - Rawze - 04-05-2026
I keep saying it but no one believes me.... Trash can overhaul parts usually = trash can results.
Also,.. I would fire the person who did that crappy counter-bore job. Those numbers are all over the place. If someone did that to my engine, I would make them do it again and correct it!.
- Here is how accurate it is when someone takes their time and does it right ...
info: https://rawze.com/forums/showthread.php?tid=1388&pid=11611#pid11611
I would not give you 3 cents for that engine in the condition its in ... none of the components in it are worth putting back together at this point. - And if some shop machined that top deck ... waste of time ... Its time to throw it away!!!. I have seen where 0.002" shaved off the top deck, even if done well, ruins an ISX block.
Also.-> The front exhaust side, right and/or especially, the back intake side coolant passages are notorious on an ISX to get leaky on a badly abused engine. This is why the OEM head gasket has those laminated layered corners .. to help stop it.
To me,. it also looks like someone smeared waay too much aerobic sealant in those areas as well. I have done blocks that were pitted to h#ell and beyond on those corners, and never had to use that much sealant for it not to leak... matter of fact,, I have never had one leak like that after I got done with it.. but then again.. I only ever use all OEM parts including head, etc... and clean up the deck myself
Also... that top deck looks terrible overall. I clean them by hand.. + hone only enough to get back down to, and reveal the original machining marks from factory again,.. and no deeper... and not with a godd#amn wire-wheel and other harsh methods like was clearly used on that block. Its scratched all to h#ell in 50 different directions.
I.E.> I would also fire whoever scratched up that top deck so badly with an abrasive wire-wheel, sand paper, or whatever garbage they used.
- If you can't see those original factory blanchard-grinder machining striations, usually with some bit of normal galvanic discoloring (blocks with a lot of miles on them), revealing them all the way across that top deck, then something is wrong!. - Usually, its due to some yahoo that dug into the deck too deep with power tools and wire or sander wheels, etc. ,... trying to make it all shiny again, like an utter complete fool!.
Trying to make the top deck perfectly shiny is a MISTAKE...
Here is a perfectly clean and leveled top deck, ready for a new head and head gasket. It should typically look like this ...
[attachment=10253]
(right click to see bigger image)
This is one of the things I specifically look for when inframing one... and hence WHY I do not use any abrasive or powered cleaning methods on them.
In the photo(s) that you provided above... To me, it looks like the whole top deck on that one is ruined at this point.
RE: Coolant leak inbetween head and block. - mechanixrds - 04-06-2026
I am 100% a believer in aftermarket parts being complete trash now. The pictures of the block I posted were after the machine shop decked it. We don't use power tools on the deck when cleaning the residual head gasket material. The protrusion measurements are quality issues with aftermarket parts, in my opinion. If anything, others should learn from my mistake and see why aftermarket parts are garbage. The proof is in the pudding.
I did measure the dowel pins, as Nostalgic mentioned, and dowel pin bores in the cylinder head and measured .0472" on both.
Besides aftermarket parts and replacing the block, are there any other suggestions or recommendations you may have?
RE: Coolant leak inbetween head and block. - marek4792 - 04-06-2026
The big problem with aftermarket is the inconsistent quality of parts. You could take it to the world's best engine builder who does absolutely everything right 100% to the book and it will still be trash at the end of the day.. Can't say it won't happen with all OEM parts (ask the CAT folks how's that going..) but atleast you will have a parts/labor warranty. That's why Rawze and many others on here heavily push the use of OEM parts..
RE: Coolant leak inbetween head and block. - mechanixrds - 04-06-2026
(04-06-2026 )marek4792 Wrote: The big problem with aftermarket is the inconsistent quality of parts. You could take it to the world's best engine builder who does absolutely everything right 100% to the book and it will still be trash at the end of the day.. Can't say it won't happen with all OEM parts (ask the CAT folks how's that going..) but atleast you will have a parts/labor warranty. That's why Rawze and many others on here heavily push the use of OEM parts..
I 100% agree with you.
RE: Coolant leak inbetween head and block. - Rawze - 04-06-2026
(04-06-2026 )mechanixrds Wrote: ...
Besides aftermarket parts and replacing the block, are there any other suggestions or recommendations you may have?
This is the way an ISX should be inframed. Anything less, and it will not be a million mile build.
info: https://rawze.com/forums/showthread.php?tid=8105&pid=70606#pid70606