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Hello felas. I am new to this site and I am looking for a little advice on the updated 6.5 blocks. I picked up a really nice 1993 chev dually 4x4 for a smokin deal. So I thought I will put an optimizer block in ... JOIN NOW TO REMOVE TRACER

new 6.5 blocks

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Old 02-24-2012, 07:51 PM

Default new 6.5 blocks

Hello felas. I am new to this site and I am looking for a little advice on the updated 6.5 blocks. I picked up a really nice 1993 chev dually 4x4 for a smokin deal. So I thought I will put an optimizer block in it. I am more familiar with the old faith full 6.2. I have found a new long block for 5100. But the block is a #506,heads are 10137567.Is this a good block and heads? Better than stock? Holy snappin arsholes there is a lot to know about where my 5000 bucks is going.
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Old 02-24-2012, 10:24 PM
Diesel Wrench


Hi welcome to the site. If it was me I would stay away from the 506 blocks. They have oil cooled pistons and are prone to main web breaks. I would ether find a late 6.2 or 599 block 6.5 and build it. I am replacing a 506 block in a suburban that cracked a main web. The guy who owns the suburban is getting a new complete 6.5 from peninsular diesel for $6500 dollars. I know $1400 is a lot of money extra but I would skip the late 96-97 and 506 blocks and go older or newer.

2MuchJunk's Sig:83 Chevy 4x4 6.2 diesel forged Teflon coated pistons, total seal gap-less rings, balanced, banks turbo when I get motivated enough to put it on, soon to have head studs, main studs, and a fluid damper.
95 GMC 6.5 bad trans at 300k. 94 1 ton 6.5 beat up and wore out, 94 1ton dually ext cab 4x4 5 speed.
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Old 02-24-2012, 10:41 PM
luke22494's Avatar
Diesel Fan
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so a 94 block should be good

luke22494's Sig:94 chevy silverado 2500 hd 6.5 td 4x4 5 speed, relocated pmd, full flo pro 4 in straight pipe all the way back with a flo pro 7 in tip , boost gauge runnin 14 psi,egt and fuel press gauges and 1 mm os bump, soon to come:5 position shift-on-the-fly chip
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Old 02-25-2012, 12:46 AM

Default 6.5 blocks

Thanks for the info. Is there a casting number for the better blocks? I would rather go new.There seems to be a lot of long blocks out there that are new but of old stock.Are there updated blocks made by different companies?I have heard of guys talking about a "F" block. What is that?
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Old 02-25-2012, 12:58 PM
Diesel Wrench


The 94 is good block. The F code just means it has no egr on it. If you want to go newer you need one made by GEP and cast by International. I would watch out for any of the updated or new blocks around most of them are Chines and not worth a crap. The newest P400 6.5 is the best, then the Optimizer, then I would skip all the way back to the 599. Any thing newer than a 599 block that was in a gm truck I would not run unless you just need to get by.
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Old 02-25-2012, 10:06 PM


Would you rebuild the 1993 block? The fella said there was oil coming out of every were. If the block checked out to be good no cracks would it be worth rebiulding. The heads are #10149599The motor had allmost 300.000 on it before it give up.I tried to see a casting number on the 93 block and all i could see is 50cfo if that makes sense.

Last edited by logger33; 02-25-2012 at 10:09 PM.
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Old 02-25-2012, 11:02 PM
Diesel Wrench


If you remove the intake the block numbers will be cast on both sides of the lifter valley. If the block checks out good I would rebuild it. Why did the engine fail?
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Old 02-26-2012, 08:48 AM


I don't know.All i was told is there was oil coming out of every were.Maybe a hole in a piston.It was pressurizing the crank case.
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Old 02-27-2012, 11:13 PM
Jeff Bennett's Avatar
Diesel Fan
Bennettjeffrey Major Las Vegas
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I could be the crank case breather. Same as a PVC valve but it is 125.00 and dealer only item. It is mounted to the RT(passanger) side valve cover. It is a metal tuna can looking thing that goes into the hole in the pass side cover.

I know it is 125.00 but that is alot less than 6500.00

Jeff Bennett's Sig:1993 GMC K2500 6.5 TD. Engine, Standyne pump, injectors, and glow plugs all replaced 1/12/12 10" Lift, 37" Tires, Pod guages(EGT, Boost, Transmission temp)Cayt Removed 3" straight through exhaust.

Truck is Black(Murdered out with a wrap), and Silver.
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Old 02-28-2012, 12:27 AM
great white's Avatar
Diesel Enthusiast


New optimizers all have "506" cast in them like the last gm production blocks. They will have the international double diamond in the valley. They also have different casting numbers than the gm blocks. Here's a picture of my optimizers lifter valley and the international markings:

Click the image to open in full size.

Click the image to open in full size.

Any gm block that's been magnafluxed and found to be crack free is a decent rebuilder. If it's not cracked by now it's a reasonably stable casting. However, be aware that they're almost all cracked, even the "fabled" 599 block. Mine was....

What does "oil from everywhere" mean?

Leaking from crank seals, valve cover, etc or was it blowing liquid oil out the filler tube?

Oil seeping everywhere is just an old tired engine. Spraying oil out the filler tube is a collapsed piston crown ( I've experienced that too), fragged rings or a scored cylinder bore.

The crankcase valve is properly termed am crankcase depression regulator (CDR). Unlike a pcv valve, it limits the vacuum that the engine pulls on the crankcase.

Now, reality check; if you've got lots of blowby in the crankcase and a high mileage engine, it's probably the rings and not the cdr.

Google "water test" and "6.5 diesel" to get a simple check you can perform to give you an idea of how bad it is ( or isn't).

Sent from my iPhone using Tapatalk

Last edited by great white; 02-28-2012 at 12:29 AM.
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