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6.5 turbo diesel blues

28055 Views 38 Replies 15 Participants Last post by  Schoust
Well I bought another truck... and it's a little noisy.. :drunk: I DID get a screamin' deal on it because of the engine problem (or so I think). All I want to end up with is a budget tow rig. I figure a rebuild is in order- but I don't know these diesels. Could be something more simple. This one has 212k on the clock. I made a short video to help diagnose.

Any diesel tech's out there?
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sounds like valve train problem.These have hydraulic roller lifters on could be collapsed or a rocker or pushrod problem.
Thanks for the reply.

I'm a little apprehensive on starting/running it and killing more parts but I think you are right by saying valvetrain. The fact that it still carries 40 psi at idle may very well rule out bearing failures.

Will a stuck injector will cause a diesel engine to make nasty sounds like this too?
With the type injection system on this truck highly unlikely.The injection pump on these functions about the same as a distributor only instead of sending spark to the correct cylinder at the right time it injects fuel under high pressure.It really sounds like valve train I would pull the valve covers and check pushrods, lifter preload, broke rockers etc. first.
Also check the flexplate for cracks this is common.
It sounds like a valve train problem. However injectors on a diesel can make a terrible racket too.. Does the white smoke clear up after you get warmed up?? You may have a blown head gasket too.

I pull the valve covers and check for obvious problems.

You should be abel to read some codes with a code reader.

I'm not too familiar with GM diesels but it should start a lot easier than it did. There is probably a lift pump either inthe tank or inline. This supplies fuel to the injector pump. If these go bad hard starting is just one of the problems they cause.
Here's what caught my eye... oil pressure. 40 at idle is fine, but take a look at the temp gauge too. my stock 6.5 will almost peg the oil pressure gauge at cold idle. Then near the end when he revs it, the oil pressure doesn't rise much at all.

Its possible you lunched a main or rod bearing, but it sounds more like a valve issue. Mains and rods tend to clunk more than tick. If the smoke is blue, its oil. If its white, its diesel. If its diesel, you're in for injectors most likely unless the timing is way off. If its oil, you're in for at least rings.

But, the good news is that the rest of the truck looks nice, the alternator looks brand new, and even if you have to rebuild you still have a really nice truck.

The stock 6.5 has a couple weak spots. First of all, move the injector computer away from the engine. It can't take the heat and likes to die. Many aftermarket companies sell kits to do this, or you can get creative. There is rumor that the block decks and/or head decks are thin on the civilian models, but I've run two of them senseless and never had a head or block failure, nor a head gasket failure. But if you want to remedy that issue, just get a military block to replace it.

Stock HP ratings were 180-200, but don't let that fool you. They make more than enough torque for towing. If you want to up the ante a bit, intake and exhaust FIRST. That should give you a nice boost, but if it isn't enough go with a mild chip and an EGT gauge. With diesels you always improve airflow first, then add fuel. If you do it the other way around, your EGTs will spike and damage the turbo. Keep EGTs 1200 or less and all will be well.

What I would do first is use the screwdriver-to-the-ear trick to narrow down where the noise is. If its up top, pull the valve covers and diagnose what's wrong and fix it. Have spare valve cover gaskets handy since most of them came with cork/rubber gaskets that will leak if you try to reuse them. Then check the injector timing to see if the smoke is from retarded injection. Maybe pull the injectors and have them tested and rebuilt if necessary to get rid of that smoke... unless that's oil smoke in which case you'll need a whole rebuild - the extent of which can be determined between you and your machinist.
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1993s had full mechanical fuel injection pumps, 94s went computer. sounds like wrist-pin , they had a rash of wrist pins breaking hear.Sounds like the engine is in very tough shape as even with 1 bad injector it would start better. put a gas in it the 6.5s are not a great engine . at least the 1 i had plus a customer had a fleet of them,sent them back after several years of grief.
I am with the valve train issue first but it has a dead hole when you are cranking it listen for the skip. White smoke on a diesel is unburned fuel most times than not and the puff puff out of the exhaust is in time with the miss/knock. Yes a bad injector will make noise hence the term injector knock. I would run a compression check to see what VC to pull off first.

I delt with one of these things for a short time and learned a little. First, they have alot of weak points, are expensive to work on, and are short on durability. They are notoriously hard to start if you have a bad set of glow plugs or something is not perfect. Mine never started quickly unless warm. Diesels can make nasty sounds with bad injectors so if you can have them tested cheaply it might be worth a shot. This could also explain the horrid amout of smoke. As mentioned computers can fail and cause all kinds of issues. The comment about checking timing is only valid if this is a 93 back since later are electronic. If the earlier there are timing marks on the pump where it goes in the block. You can see the marks with the cover off looking behind the water neck with a flashlight. The cracked flywheel is also worth looking. When I boat anchored my engine I found a cracked flywheel.

The best thing you can do is go to a 6.5T site and talk to the guys that know and like these engines. Most anyone else is gonna tell you they are junk....I would tend to lean to this side.

When mine broke a pulley and overheated, I yanked it out and replaced it with a cummins. Never looked back.
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I agree that 6.5s aren't the greatest diesel, but they are far better than 90% of the gas engines out there. I'd rather have a crappy diesel than a great gas engine. I would rather spend the money to properly address the weaknesses of a diesel than to spend $500 dropping a gas engine in it. Anyone who has used a diesel to tow heavy loads would probably agree. There is just no comparison when you're towing 10k, your foot is to the floor and you top a mountain at 65 mph with the coolant at 180 degrees while getting 16 mpg.

I had my 6.5 (98 1-ton) pulling my 10k travel trailer from Phoenix to Flagstaff. Phoenix is at 1000 ft elevation. Flagstaff is at 7000. That's 6000 ft up and down in 150 miles. This was in July, and the temperature in Phoenix was 115 when we started. The whole trip I could choose whatever speed I wanted, the temp never went over 200, and the A/C was keeping us nice and cool. The bonus was we made that particular leg at 12 mpg. I don't mention this to sensationalize the topic, but when it comes to towing, diesel definitely gets the nod.

... well, I can think of SOME diesels that I don't want :) 80's BMW diesels come to mind :)
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Good info guys. I am eager to turn wrenches on it. I'm admittedly not a diesel fanatic but since this thing will be the new tow rig, I may change my mind. I like the fact that I darn near stole this truck.

It's a '93 1 ton. Mechanical IP. Interior is nearly perfect. I'll be hotrodding a 6.5TD if a rebuild is needed-(maybe soon :D ). If I can get lucky and 'make the bad things go away' I'll drive it until I gain the knowledge (and thick skin) to have a 6.5 that will get out it's own smoke. Seems all problems with the 6.5TD is cooling/owner related. At least that's my take as I'm just starting to wrap my head around the whole 6.5TD scene. (that's a lot of wrapping)

The white smoke is pure unburnt diesel. And 40 psi while cold may not be what it needs to be. I can't help but think it's an injector stuck open. Yet it does have a metallic valvetrain sound.

I will be sure to post updates.
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curtis73 said:
Here's what caught my eye... oil pressure. 40 at idle is fine, but take a look at the temp gauge too. my stock 6.5 will almost peg the oil pressure gauge at cold idle. Then near the end when he revs it, the oil pressure doesn't rise much at all.
I just watched my own video again and when the RPM increased the oil pressure decreased..! Hmmm. That was the first time I actually heard the truck run. The previous owner said it was blown and this is what he'd take. I said, deal. So I drug it home and got out the camera and here we are. I have all the patience in the world.
I would strongly urge you to think about dumping the 6.5 if it is not an easy fix. You can bolt in a cummins if you have any fab skills at all and you will be so much happier with that engine. I had both and there is no comparison. There are a couple of trucks in town where I am just like yours running cummins. They can be had for the cost of what it will take to rebuild the 6.5 if it has been severely overheated. My 6.5 sounded better than yours with two cracked heads.....
If you think it is an injector start the truck and crack open one line at a time. This will prevent that injector from firing.If a miss is not created when cracking the line you found the bad hole.Works the same as pulling a plug wire to isolate a miss.
Ok, today I cracked open some injector lines and noticed a difference but the knock never changed in intensity. The engine just developed a dead miss as I opened the fitting. That's all. Todays run time (only my 2nd time starting the thing) was a LOT more like the sound of a rod bearing.

Upon firing up the engine today there was a very noticeable SQUEAK until the oil pressure came up, which by the way is getting less and less. :(

Still haven't pulled any valve covers. May skip that exercise.
Just a thought... You can spend the money on a rebuilt 6.5 with upgrades, or you could buy a 12v cummins and shoehorn it in there. :) That's one easy way to sidestep any shortcomings (or shortcummins :)) of the 6.5.
Painless has a wiring kit for the 5.9 12valve Cummins. It make a great swap. Just make sure it has a good transmission. A guy I work with is about ready to do the Cummins swap with a NV-4500 5 speed in his chev dually.
Actually, the 12 valve Cummins is a really good idea. Lots of kits and parts available for the swap, and way more torque and power than the wheezy old 6.5. Try here for some Cummins swap info.
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