There is very little difference between a 6.2 and a 6.5 engine. The only real difference is the bore 101mm for the 6.2 and 103mm for the 6.5
The late 6.2 90-92 shared the same block and crank with the one piece rear main seal as the 6.5.
These engines used the 599 block that was just bored a tad smaller. The internal stuff like the crank, rods, cam, timing gears, rockers, pushrods and such are all the same.
Heads are virtually identical with the exception of the precups, which saw a myriad of port sizes over the years.
The early 6.2 had a small precup port which really helped the MPG the higher power engines (J code) had slightly larger ports. The 6.5 TD engines had the largest ports.
As far as problems go, any and all of these engines can break cranks, crack main webs and crack heads. I have been inside these diesels from 1982 Red engines all the way up to 1999 6.5 Turbos.
I have seen a 6.2 run 300K with zero issues other than injectors and an IP change.
I have seen them come apart "Boom" at 50K miles with a broken crank
Head gaskets seem to last somewhat longer in the NA engines BUTTTTTTTTTT the early 6.2 engines used a gasket that was a tad iffy at best.
The latest incarnation of the 6.5 gasket from felpro is about the best there is for thes engines.
Cracked main webs has been a curse from the gitgo. Many of these engines will develop cracks in the main webs and still run a long time without symptoms.
cracks in the heads betwen the valves is also an issue. Most of these cracks do not cause failures but they can eventually go through to coolant and result in problems.
The holes in the bumper (Nostrils) were installed with the 6.5 TD to allow more airflow into the radiator and oil cooler area.
Exactly how much they help, I dont know.
The longevity of these engines is the result of several factors. Overheating is a quick trip to trouble. Overheating takes a terrible toll on head gaskets as well as the heads and the block.
Good maintenance is by all means a real plus. Under most conditions the 6.5 TD will make about 200K to 250K before the head gaskets fail.
I have seen a little less as well as a little more.
I have seen engines with 250K miles that looked pretty much like new inside with no wear in the cylinders and the bottom end was spiffy also.
I have, on the other hand seen some real trash too with far fewer miles.
Timing chain wear is normal but the sprockets seem to last well. I have installed a fresh chain at 200K miles using the original sprockets and all was well again.
I have seen cranks with 200K+ that look like new.
The main web cracking seems to ellude most speculation as to when or why it happens.
I have seen 200K miles and zero cracks and 100K miles and just JUNK.
We have beat the ideas about for years as to why these things crack and the theories are as varied as the number of folks adding opinions.
My best educated guess, barring a bad vibration damper is that some of the block castings were GREEN (as in uncured) and as the duty cycles progressed, the castings settled in and moved around resulting in cracks as the metal moved and normalized.
GM made several changes in things in the block and the cracking issue never really went away.
They reduced the diameter of the center outer bolts from 12mm to 10mm to try and stop the cracks in the outer holes, to no avail.
The late 97-99 blocks would crack the number 8 cyl wall about 1 inch down from the top near the back wall.
The crank breakage was yet another nightmare. I have seen 200K engines that the cranks were totally crack free when doing a magnafluxing and then see an engine with 50K miles snap the crank.
A broken crank is usually a death sentence.
Some broken cranks have been seen in Burbs used to get the groceries and haul the kids to school, having never been used hard at all ?????????
Others get the crap beat out of them and last a good long time and never break.
My take on this is that during the casting process some crank castings vevelop porosities, eddy current flows in the grain structure and possibly other weaknesses that result in the failures.
My personal recomendation is that if you are building a fresh 6.5 that you use a fresh SCAT steel crank. This is not a Bank breaker at around $300 or so if you shop around.
The problem with a cast iron crank is that it is contantly flexing and moving, although only slightly, it is constantly flexing a little. Over time, just like bending a paper clip, sooner or later SNAP it will go away.
Cast iron is not the best choice for a crankshaft, especially a diesel crank.
Variations on the injector POP pressure between the cylinders does cause variations in the cyl-cyl timing. This can and does cause tortional vibrations to set up in the crank and the block. This issue over time, dependng on the severity, IMHO can lead to cracking and or crank breakage.
The SCAT 9000 series crank is a cast steel crank, although not as good as a forged crank, its still better than a USED high mile cast iron stock unit.
Bill Heath has been using the SCAT cranks in the Salt falt truck and recommends them.
I have one sitting here thats going in the AMG Block for DaHoooley.
I have two perfect stock GM cranks sitting here too, but I am not gonna take any chances with this one.
Fresh zero hour Block, Fresh zero hour crank, Fresh zero hour heads.
In closing, the failure rates did tend to escalate when the turbo was added, likely due to more heat and stress on the foundation.
Keeping the beast cool is the prime concerns.
The radiators in these trucks from the factory are TOOOOOOOOOOO small. \
The simple fact that the size of the front of the truck does not allow enough room.
YESSSSSSSSS I know, you have towed all over the planet with your 4000 foot fiver and never had issues, yet the fact remains that the cooling system on these is MARGINAL at best.
SOOOOOOOOOO if your rebuilding your engine, toss that 200K mile radiator and get a fresh VISTEON OEM quality radiator. Makes no difference how good the old one looks, deep inside where you can't see it, time and chemical action has deposited a layer of insulating crap inside the tubes that effectively reduces the cooling ability a BUNCH.
NUFF for now
Missy
