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| Let's talk about cylinder head cracking! http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=90438 |
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| Author: | flash7210 [ Sat Sep 21, 2019 12:25 pm ] |
| Post subject: | Re: Let's talk about cylinder head cracking! |
GordnadoCRD wrote: 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. Are you saying that the operating temperature of the engine should be increased? To me, is seems that the operating temperature should be decreased. But I guess that depends on a variety of factors. If the operating conditions dictate the engine to run at 220F, it will do so, regardless of the operating temperature of the thermostat. Or are you saying that the coolant/water ratio should be changed? Or at least carefully monitor coolant ratio and condition? Straight water has a greater heat capacity than coolant. But coolant has a higher boiling point. I would never recommend running straight water (corrosion). Best to mix in some ratio like 50/50 or 60/40 (water/coolant). It seems to me that coolant flow, or lack there of, is the main problem (i.e. inline thermostat). After replacing my cracked head I had a theory that maybe the rearmost cylinders were running hotter than the front. So I stuck a temperature sensor on the side of the head between cylinders 3 and 4. Its not really the best sensor. Its not actually inside the head. Just stuck to the side. But it gives me some interesting data. 1. once everything is fully warmed up and I'm cruising at highway speeds, the cylinder head temperature is consistently ~20F cooler than what the coolant temp sensor is reporting. 2. when I slow down and have to stop at a light, cylinder head temp starts to increase. If I'm stopped long enough, cylinder head temp will eventually match the coolant temp. This tells me that when then engine is operating at a higher rpm and there is good airflow through the radiator, the coolant is doing its job by pulling heat away from the head. Mainly due to increased coolant flow. (hey, its the best I've got to go with. Feel free to scrutinize those details however you wish) Lastly, the symptoms of the cracked head were present before I did any kind of ECM tuning. Just using a stock tune. Although I was ignorant to those symptoms at the time. |
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| Author: | GordnadoCRD [ Sun Sep 22, 2019 11:29 pm ] |
| Post subject: | Re: Let's talk about cylinder head cracking! |
I guess what I'm saying, is there's more than one way to skin a R428. What I'm NOT saying, is that I know what way is best. Or that I've thought of every solution. The more detail you've given, the more I think of inconsistency in casting Inconsistency in material EPA regulations requiring the domestic Jeep version of this engine to be run with coolant colder than the Euro/export versions. (which could explain why this problem seems to be more pronounced here, than in those versions.) |
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| Author: | Diesel Dan [ Mon Sep 23, 2019 11:28 am ] |
| Post subject: | Re: Let's talk about cylinder head cracking! |
Root cause....poor design. As we all know the Dmax is aluminum headed as well. Quote: Time is an important factor in determining maximum acceptable EGT. The LLY/LBZ is rated for 1365 degrees F continuous and/or up to 1435 for 5 minutes or less. We've seen 1400 or a little more for completely stock LLY's during a Pull-Off here in Montana. We also know that a Duramax can tolerate 1800+ degrees during a 1/4-mile run with lots of fuel and nitrous oxide, and for those willing to accept more risk. It's only there for a few seconds, which helps make it tolerable... https://www.thedieselpageforums.com/tdpforum/showthread.php?t=23047 AND they don't drop valves, even after 500k miles of towing hotshot. |
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| Author: | flash7210 [ Mon Sep 23, 2019 12:15 pm ] |
| Post subject: | Re: Let's talk about cylinder head cracking! |
Quote: Root cause....poor design. Can’t argue with that. Unfortunately there’s nothing we can do about it. I guess the best we can do is manage EGT and maintain good coolant flow. |
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