New Engines for a Hummer

Cracked Block Article

If this site has helped you consider a Donation. Donation Info

The latest information (8/8/2010) on a great replacement engine is the GEP / General Engine Products - AM General P400 engine or block. A P400 longblock costs 5625.00 plus freight. The P400 has a stronger crank and bottom end and a significantly beefed-up block. The whole motor is designed for an intercooler and other bigger-power options. The old motor parts transferred to the P400 longblock without issue. Although the block dimensions are different, all the critical holes are the same size and in the same place with only two exceptions; the bell housing bolts and engine mount bolts are metric. The motor fit with one minor exception; a small part of UCP under the oil pan had to be bent down a couple of inches.

From what I've seen I'd budget at least 10k for the full job. If you go to a dealer budget 15k. This includes removing and replacing. I know some owners who are skilled enough to pull an engine themselves which will save a bunch of money. The AMG book time in Jan 2001 when my engine was replaced was 24 man hours. That would translate to 2,400 in labor at the dealers around me. Then you will have misc parts and all the fluids to pay for.

You can purchase new engines in any configuration you want. The price range is pretty wide. New engines DO NOT come with starters, alternators, power steering pumps, sensors, air conditioning compressors, wiring, control computers etc. All this gets moved over to the new engine. Depending what you're buying you might not get the injector pump, turbo and many other parts. If this is that case you might want to have the injector pump rebuilt and get new injectors.

Since the whole thing is apart I would replace the serpentine belt, all the hoses and maybe the motor mounts. When I had my 98'sengine replaced under warranty the new engine had a different water pump which was designed to match up with the newer style fan clutch mount. Luckily I was there because they were going to take the old water pump off the blown engine and install it on the brand new engine just to make the fan clutch fit. I paid 100 extra and bought the new fan clutch which allowed me to keep the new water pump. If your truck is an older one with the very noisy steel fan you should get the new fan clutch and the plastic bladed fan. The whole cooling stack will be out of the truck. If the truck is older It might be wise to have the radiator and coolers sent out to a radiator shop and boiled.

I also took advantage of the fact that it was all apart to add the boost and turbo inlet temp gauges . The sensors were really easy to mount with the engine out. This would also be a good time to line the engine cover and surrounding area with sound reducing material. I have articles on both of these subjects.


Where to Buy a New Engine & Parts
Disclaimer - I don't have any direct experience with the companies listed below, so it's buyer beware. Prices are from the summer of 2003


Diesel Depot (478) 552-9510 Have the new AMG block, do upgrades like 18:1 pistons, balancing and the gear drive, porting of the heads along with the ceramic coating on the pistons. Jamie at The Diesel Depot has this all made up on his shelf and selling it for around $5,600 in long block form.

Prices as of 6/15/2004

1. Rear Turbo Long-block: $3250 exchange (or add a $700 core charge)

  1. Ceramic Coated Exhaust Manifolds - $160 exchange (or add a $250 core charge)
  2. FSD Cooler (cools the pump mounted fuel driver) - $170
  3. Injectors
    1. Stock 6.5L Turbo: $300 per set w/ install kit
    2. High-Flow Injectors: $590 per set w/ install kit
  4. Glow Plugs
    1. Stock: $46 per set
    2. LDM "Quick Heat": $96 per set
  5. Port Matched Intake Runners: $125 exchange per pair (or add a $200 core charge)
  6. Boost Control
    1. Turbo-Master Adjustable Boost Controller: $120
    2. Electronic Boost "Cheater": $100
  7. Performance Computer Re-program: $650 exchange (may have to ship your computer for programming)

Kennedy Diesel (715) 255-9433 Kennedy diesel has full drop in AMG engines for $6250 in stock form or AMG long blocks for $3,950.

Peninsular Peninsular diesel (616) 530-1298 has AMG long blocks for $6,679 or a pumped up AMG Hummer motor with 18 :1 pistons, modified turbo and waste gate controller, custom SS exhaust elbow (replacing the HP robbing cast iron one) Boost controller for 230 hp, comes up to $8,786.

Another place is Hummer Engines (866) 526-9776

Dennis Sweeney (has done almost all racing engines for all hummers)
GEPP Diesel
15570 Red Rock Rd
Reno, NV 89506


GM Diesel Engines

Alabama Cylinder Heads


Click Here for the article on the Flash off Road Cooling Kit

If you have an engine 'At Risk' this is the only thing you can do that might keep it from eventually cracking.

Rear Head Cooling Kit


After just having about 200 miles on the new engine that some Hummer Buddies and I installed in my truck last weekend, I have noticed the following;

1) After doing routine fluid and air burping checks, I was amazed at the amount of flow that is achieved through the Cooling Kit. It makes you wonder what that coolant was doing before.
2) The heater spits out heat within 4 minutes of running from a cold engine. I believe this is due to the circulation of coolant through the heads and through the coolant kit and being dumped directly into the heater hose.

To enforce your warranty contract, check out:

Warranty Article

Lemon law America




I just wanted to plug these guys at Diesel Depot, I recently bought a 97 H1 in Florida drove it to Georgia to Diesel Depot who had build the modified 6.5 turbo V8 in the truck. These guys not only know their 6.2 & 6.5 Hummer engines but are the nicest bunch around.

They repaired an oil leak the previous owner in Florida claimed to be minor, which in fact turn out to be an obvious failed turbo, so bad as a matter of fact the shaft moved everywhere but in the designed direction. After the repair which included a new turbo unit at a reasonable price with their already new block, they offered a car to me so I could get into town while their finished the repair, and had the repair done in one day so I could continue my drive to Arizona from Florida.

Anyone here who needs or is thinking about getting a new or modified 6.2 or 6.5L engine call these guys and they will do right by you.

Well, I got my cylinder heads on tonight. Everything went very smoothly. The new 6.5 NA heads weren't in stock so I went with 2 rebuilt heads from Alabama Cylinder Head. Cost was $275.00 ea exchange. As a rebuilder myself, I am usually very critical of others' rebuilt parts, but I must say that I was very impressed with the quality and workmanship of these heads. I recommend them highly.

Rebuild for a mechanical Injector Pump

Call Taylor Diesel in Nashville. I got mine for about $400. 615-242-9550, ask for Carl

Here is a short blurb from Kennedy's site that explains the new Fan clutch:

"Based on my own personal experience with my 1996 GMC, and the reports from many others, the factory fan clutch calibration is much too high for proper engine cooling. The factory clutch is calibrated to engage at 1950 as measured at the fan clutch's thermostatic coil. This coil temp, while directly related to engine coolant temp, is a much lower value. In most cases, it takes well over 2200 coolant temp through the radiator to achieve this point. In fact, the "kill temp" or the specified max engine coolant temp measured at the thermostat outlet is specified at 2400. At this point the factory clutch is to be fully engaged. The rapid swing from 2200+ down to 1800 can be very hard on the cylinder heads and gaskets etc. The revised calibration shifts the engagement point downward by 150f. This downward slide moves the entire fan engagement curve lower, keeping the engine coolant temperature much more stable. By beginning the engagement curve earlier, we also improve air conditioning, transmission fluid, and engine oil cooling. In most cases, with this revised curve, complete clutch engagement is not even necessary."

The high flow water pump kit was about $440, which includes the water pump, new dual thermostat crossover pipe, thermostats, hoses, and a bracket for the throttle connection for mechanical fuel injection engines. I think it's about $75-$100 less for electronic injection. The fan clutch was $250 plus $45 for the new fan. So after everything, I'm in for about $1000 in cooling system upgrades. It's a lot of money, but after blowing a head gasket and seeing the damage to the heads, I think it's money well spent. I'm thinking after doing these mod's and opening up the exhaust, I'll have good headroom for making more aggressive injection pump tweaks.

Just a note on the high flow water pump kit. THIS IS NOT A BOLT ON DEAL FOR NA ENGINES. The problem comes with the throttle cable linkage. There is not enough room between the old throttle bracket and the new thermostat housing. The kit came with a new bracket, but evidently it does not work for Hummers. What we ended up doing is cutting up the old bracket and welding part of it to the new bracket. The throttle will work well now. Actually, I'm thinking that I may not have been getting the full travel range of the throttle before. We did have to lose the fast idle solenoid. There was just nowhere to mount it without doing more extensive mod's to the solenoid, bracket and probably the linkage on the injection pump as well. Pics in a few days.

After losing my engine, I called Jamie at Diesel Depot to order a reman long block. I decided that I would go with most of the reliability and performance enhancing options. Here's what they are doing:

1) Complete balancing of the rotating assembly, including harmonic balancer and flexplate. This will help the engine run smoother and last longer.

2) Ceramic coating on the piston crowns, combustion surface of the head, and the exhaust ports. Ceramic coating helps to retain heat from expanding combustion gasses which creates more power. It also allows the pistons to be able to handle more heat created by injection pump tweaks. I am also having my exhaust manifolds and Y pipe ceramic coated locally to keep down under hood and doghouse temps.

3) Ported intake manifold and cylinder heads. In order to make more power in a diesel, you have to get more fuel in the cylinder. It is also necessary to get more air in the cylinder to burn the fuel and to keep temps under control. This is why turbo's are so effective on diesels. Opening up the intakes will help to accomplish this in my NA engine.

4) Performance camshaft. Diesel Depot offers a camshaft with a little more aggressive profile for NA engines. Peak torque is said to be achieved about 200 rpm's lower than stock and is maintained through more of the rpm range.

5) Studs and girdles to strengthen the mains and a high volume oil pump should help to make this engine last.

I have been told that the same setup in a Chevy truck (with modified intake and headers) made about 220hp (!) on a dyno. Keep in mind that the stock NA engine is 160hp and the TD is 195hp. I don't think I'll get quite that much due to differences in the injection pump on my engine and, of course, the intake system on the Hummer, but if I get to the 190-200hp range, I think I'll be quite satisfied. I also feel that all of the cooling mod's I have done previously will be a great match for this new engine. BTW, the total cost for the long block is about $4200 exchange with a two year/24000 mi warranty.

Tips When Rebuilding Your Engine:

If it is just a head gasket, your OK (per say), it is just a lot of work to replace the gasket. However, MAKE SURE who ever does the work, uses NEW head bolts, runs the threads, and uses the proper sealant for the head bolts, some kind of high temp Teflon loc-tight, I can get you more info if need be. And since the valve covers seal very badly at the rear on the corners, double check prior to engine cover install for leaks. And by all means, cleans all sealing surfaces prior to re-assembly.

The last truck we did, we had the head magnafluxed and there was a long crack between the #8 piston intake & exhaust valve seats in the head, the crack went up into the intake and exhaust ports, the head was toast. We ended up pulling the drivers side head off and decided to replace both
heads, all injectors, have the injection pump rebuilt, new water pump, vacuum pump, crank dampener, crank pulley, idler pulley, front main seal, new glow plugs, GP wiring, GP controller, oil pressure sensor, fan clutch, alternator; since it is all off anyway. Basically, anything on the front of
the motor that turned.

The truck was a 97Turbo with 105K on it. (not mine, I did that prior)

Things to consider:
Since your truck is a 97.5 (How many miles?)
Replace all radiator hoses.
Have your Radiator/Oil&Trans cooler/AC Condenser re-cord.
Evaluate your oil lines to the cooler, R&R.
Power steering Pump, Steering Box & lines, evaluate, R&R.
High Volume Oil Pump.
Replace AC hoses & Dryer.
Head cooling Kit - MUST.

IMHO: No need to touch the timing chain.

Prior to all of this, I decided to pull the oil pan off to make sure there where no cracks in the main bearing webbing prior to doing any work on the top of the engine. Block was fine, honing was very visible. (Engine had 105K on it, he used Sync oil).

We did not touch the turbo.

All in all, the parts are close to 4500.00. The whole process takes about 24 hours, if and only if you are very knowledgeable and have all the needed tools and you have done it before. In my case, this was the fourth HUMMER that I have done this to; the first one took a lot (say 2-3 times) more time. All of this was done with the motor in the truck. During this process, we tend to replace more parts, just due to the fact that if you don't do it now, the amount of work to replace it later justifies the cost of the new parts by far.

During disassembly of the engine, just DO NOT bend the steel injector lines from the pump to the injectors, From what I have heard, there is an internal coating, if it breaks off, may jam an injector open and this results in a large amount of fuel where it should not be during the compression stroke at a very inopportune time, and can trash the newly rebuilt motor.

One subtle hint, when we install new heads, we have two short head bolts (per head) that have the hex head cut off and have a slit cut in them for a flat head screw driver. This way you don't risk damage to the new gasket trying to place the head down the first time, the bolts act as an extended guide pin, once the head is seated, we simply remove the "guide pins".


If it is a blown head gasket use the best gaskets and head bolts out there which are fel-pro Teflon coated gaskets and ARP (Automotive Racing Products) studs. I've been told that the GM TTY (Torque-to-yield) head bolts are a very poor design for cylinder head retention and sealing because once a fastener has reached its yield point, its performance is unpredictable

ARP makes 8740 chrome-molly steel cylinder head studs that fit all 6.2/6.5 GM diesels. These are 190,000 psi tensile strength fasteners that provide superior clamping force for the critical head gasket seal on these engines. The ARP bolts are about $5.00 each ($170.00 a set), so they cost more than replacement TTY bolts. Anyone who has ever had one of these engines apart for head gasket problems ought to spend the money for the superior ARP product. Because some of the head bolt threads protrude into the water jacket, use a thread sealant on the threads. I found the best sealant to be three turns of Teflon tape, used on the lower threads only.