Ok. The 6.5 has a bad reputation for acceptable reasons. Knowing the issues that exist and making corrections is what makes it a good engine.
Get your popcorn ready:
Ive seen enough military take outs that died within 20,000 miles that I have a hard time not suggesting pulling the engine apart. Now, how much $$ becomes what improvements to make. Deflashing the block & heads is smart. Inspect and plastigauge measure bearings. Replace if necessary and if affordable have new ones coated.
Doing that you HAVE TO replace main bolts. Stock is fine, getting halo girdle kit is better.
If any way you can afford it- have the lower rotating assembly balanced. This engine is probably the worst unbalanced v8 ever made. This becomes a big part of long life imo.
A nice improvement while there is gapless rings- engine oil is much cleaner from this. Read warwagon post about his with pictures of the dipstick.
Improved oil return path with a die grinder in block and heads is helpful for high rpm hiway use. Easy for first timer to learn- a couple hundred bucks in tools- 12 hours work. Not required just a nice “while there improvment”.
You will see which precups you have while heads are off. You can consider improved valve springs. Some folks go to head studs- most don’t need them so new head bolt kit and new head gaskets.
Our rocker arms are shaft mounted and use plastic push pin retainers. Very safe for 150,000 miles. Beyond that - meh. There is a bolt modification to replace them and never worry again. Or plan on replacing the plastic retainers around 150,000 miles to be safe— in the truck removing of the valve covers ruins them. Engine on stand they can be salvaged IF PATIENT & follow instructions.
While engine is apart- after the assembly is balanced… you can have the pistons coated or replaced with new coated ones. Another consideration at that time is lowering the compression ratio. Stock is 21.2:1 (used to be 21.5:1) this is wicked high by normal standards. I used to love and champion the higher ratio. Years of being proven wrong has me switching sides. 18.5:1 is the normal lowered amount that lets the engine work less, and put more load on the turbo. This is a big part of how other diesels have more power and still ok mpg and not beat everything up. Remove the original design had NO TURBO. Stupidity at its finest. A vendor here (and many year helpful member before becoming a vendor) Twisted Steel Performance makes both 18.5:1 and is the only one making 18:1 pistons that have valve reliefs cut into them. He also sells the valve springs mentioned earlier. Some reading will teach valve float & hit piston isn’t uncommon, near garuntee by 300,000 miles as factory springs were never made for turbos. Then the timing chain stretches and best suggestion is replace at either 100,000 or 150,000 miles being sure to get the right brand. When available there is a gear drive set that eliminates chain stretch but isn’t always in production & currently not in stock so good luck getting someone to sell theirs that on the shelf for future build plans. Don’t panic- just plan it out and it’s fine. There are other things that get changed at 100,000 mile interval like harmonic balancer and adjacent pulley. For people spending money there is a better balancer that will outlive a few engines and run smoother the whole time but is near $500 nowdays. Otherwise the $120 AC Delco gets swapped in at 100,000 mile interval-
In the huge fleet we did timing chain, waterpump, front main seal, balancer, pulley all new every 100,000 miles and they paid for themselves in reliablility.
Run the proper oil filter, never miss oil change. Use hydraulic line like a backhoe has for oil cooler lines and good cooler. A good hmmwv take out is perfect for cooler and lines.
Radiator, fan, etc. you are running a big radiator- NO EXCEPTION. These idi diesel put out tremendous heat. Please- measure how big a custom radiator you can fit now. This might end this engine choice 100%. Overheating is the #1 killer of this engine. You will want an intercooler for the turbo. Oil cooler is required. Do you have more for the cooling stack like ac condenser, automatic transmission, power steering cooler?
Are you running 24volt/12volt combo or 12volt? Only run the AC Delco 60G glow plugs. The ones the military uses are 24 volt and not self regulating. They loose engines to them often. The starter on there is 24 volt, insanely heavy and you will need to build a very strong and accurate mounted (location) front support brace. And they fail about every 30-35,000 miles. They cost about $1,500. The 12 volt Hummer version is same cost, slightly longer life and an even bigger mistake requiring same ridiculous bracket.
12 volt AC delco mini high torque is about $150ish. Lasts like an average pickup starter. Best is Powermaster 9052 is like $320ish and amazing how well it helps the high compression engine start. Money well spent if affordable. Both these require a bracket for the engine and is like $12.
Your injection pump has 24 volt components in it. You can replace them with 12v parts for $100 ish.
Hmmvs have a mechanical fuel lift pump mounted on the side of the engine. GM stopped it because they were destroying engines under warranty. I strongly suggest eliminating yours. Remove and block off plate is easy- and $20ish. The replacement electric lift pump becomes pricey.
Arguments of what to spend $100 to $800ish for it with the best fuel filters and water separator available. I strongly suggest the best set up. Buy once cry once, less maintenance time, best security against replacing your injection pump and injectors. The military fuel filter is Joke at best. Poor filtering, expensive filters that are hard to get often. The pickup truck/ hummer FFM is ok but still horrible at water seperation, ok filtering, medium price on filters. Replacing heater unit usually around 200,000 miles and most do FTB modification to help out it’s inadequate design.
You WILL have to replace your thermostat crossover for long life issues of the engine. Stupid low survival rates beyond 50,000 miles in the overheating and this is part of it. Plan on $150ish here. You need. Surge tank not an overflow tank. Steel or aluminum- dont waste time on existing plastic tanks on custom builds.
Read about balanced flow cooling. You should have the proper waterpump.
DO NOT GET REAR HEAD HOSE KIT!!
