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Old 12-31-2007, 12:25 AM
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Opinions or Experiece with GM 6.5L Turbo Diesel?

I just picked up a 98 crew-cab dually 4x4 with the 6.5L Turbo Diesel w/139k and the heads and intake recently redone.






I just drove the truck home 195 miles.

The rig pulled hard and I had the cruise control set at a non-federally mandated 80mph for nearly 1/2 the trip (to keep up with traffic flow ) - it ran strong and tight.

This is the truck I've wanted for a long time - but I didn't go into this purchase with a motor preference (other than a 454 or Turbo Diesel) so I'm just looking for opinions or others experiece with this motor setup.

Thanks!

The one with the most toys wins...

Last edited by Rambo_The_Dog; 01-01-2008 at 09:59 AM.
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Old 12-31-2007, 01:52 AM
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That's almost exactly like my dad's truck; except his is a non-dually with leather.

The engine is a 6.5L. 98 was the last year of the 6.5 in the light trucks. The engine itself is pretty bulletproof. The turbo is very modest. The main weakness is the injector pump. Its just not very reliable. They should last at least 60k, but just expect them to be the weak point. Stock power output was 180 hp, so its not the biggest hot rod, but it has lots of potential. The aftermarket has plenty of chips that can pretty instantly double power output. If you want to juice things up, I suggest the following (in this order). Free flowing intake, huge exhaust, turbo downpipe, then chip it and install an EGT gauge. keep it under 1100 degrees and enjoy a happy turbo. You'll most likely need to beef up the 4L80E, especially if you plan on towing. If you feel like breaking the law, gut or remove the catalytic converter.

Nice truck!
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Old 12-31-2007, 03:28 PM
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Quote:
Originally Posted by curtis73
That's almost exactly like my dad's truck; except his is a non-dually with leather.

The engine is a 6.5L. 98 was the last year of the 6.5 in the light trucks. The engine itself is pretty bulletproof. The turbo is very modest. The main weakness is the injector pump. Its just not very reliable. They should last at least 60k, but just expect them to be the weak point. Stock power output was 180 hp, so its not the biggest hot rod, but it has lots of potential. The aftermarket has plenty of chips that can pretty instantly double power output. If you want to juice things up, I suggest the following (in this order). Free flowing intake, huge exhaust, turbo downpipe, then chip it and install an EGT gauge. keep it under 1100 degrees and enjoy a happy turbo. You'll most likely need to beef up the 4L80E, especially if you plan on towing. If you feel like breaking the law, gut or remove the catalytic converter.

Nice truck!
Thanks - just the kind of feedback I'm looking for having never owned a diesel (or turbo) equipped vehicle before.

So far - I'm pretty happy ~ I thought I might be able to hold off on new tires, but after getting a better look at them today I just ordered a new 6 way set to be installed Friday.

I've never understood why people wait so long to buy tires given the relative low cost of tires compared to the vehicle cost, the value of your life and others.

What kind of work would you have done to the trans? Is this something akin to a shift kit?
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Old 12-31-2007, 04:26 PM
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It depends on how you'll be using it. A 4L80E behind a stock 6.5 will be fine towing up to about 10k lbs for a long time as long as you don't tow in OD. The first mod I'd do is consider a trans temp gauge (I forget if the 98s had them stock or not.) As long as the temps are staying below 275 or so you should be good. You can reprogram the computer for firmer shifts which will help keep temps down some, but its a modest change, more for a performance feel than anything else. The next step (which I would consider for light towing or a chipped engine) is a shift kit. This will increase the line pressures, recalibrate shift points and firmness, and help out a lot. The ultimate (which I would probably do if I chipped AND towed heavy) is to just rebuild the whole thing with high performance guts. Its expensive, but a nice addition that will let you sleep better at night.

Another thing I'd consider is a cooling system upgrade. The 6.5s have adequate cooling, but if you double the power they won't. The aftermarket has this covered with high flow water pumps and high efficiency 9-blade fans. I used my dad's 98 to tow a 10,000 lb travel trailer cross country, and it had plenty of power to get up the hills, and it didn't OVERheat, but it did get pretty warm. The funny part is, when the stock fan kicks in, you can really feel it drag the engine down. Its pretty inefficient.

If I owned it, I would do intake and exhaust, chip it for a modest gain like 90-125 hp, install an EGT and trans temp gauge, and put my foot to the floor. Then when the tranny exploded I'd upgrade it with a performance rebuild... but that's me

Another couple tips that might be helpful; at your next coolant flush, replace the coolant with the long-life coolant offered by Catarpillar available at CAT truck parts places. Diesels use a special anti-cavitation additive to prevent the coolant from eating away the iron in the block. The CAT brand is guaranteed to not need any additive for 300k miles. I did it in my 95 Powerstroke and noticed the water jackets stayed nice and free from cavitation damage. Otherwise follow your maintenance schedules pretty closely. Diesel oil has to deal with a lot of soot particles from blowby, and it gets punished in the turbo. I used Delo or Rotella 15w40 and changed every 3000. Your owner's manual probably says up to 5000 depending on how you drive which is fine, but I'm a little more anal than that. Fuel filters need to be changed regularly. Diesels inject fuel at tens of thousands of PSI, so the fuel systems need to be clean.

Otherwise, enjoy. I love diesels and I want another one so badly I'm considering buying an old mercedes diesel just to get my fix

Last edited by curtis73; 12-31-2007 at 04:34 PM.
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Old 12-31-2007, 06:05 PM
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I would suggest you remove the big plastic cover on the engine and throw it away. Then buy a PMD cooler and install it. The biggest problem with that is that electronic injection pump. It does not like heat at all, and they are notorius for injector pump failures. The biggest thing that fails on the pump is the PMD or Pump Mounted Driver. That is the black box on the side of the injector pump. Get it off the pump and onto a remote mount so it can run cooler. You can buy the cooler on Ebay for about $60.00

http://cgi.ebay.com/ebaymotors/GM-6-...spagenameZWDVW
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Old 12-31-2007, 06:43 PM
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6.5 gm diesel

probly the 2nd worst diesel in the market only toped by the olds joke. i owned from new a gmc withe the 6.5 had 5 fuel pumps in 30000ks. frend who had several in a logging camp had wrist pins fail in 3 out of 6,eventually returning all 6. my neghbor has a 1998 which seems to do ok but it is not worked hard, has lost a trans, i would suggest do not try to take any more power out of yours remove plastic cover and inst cooling kit on fuel injection pump. service the watter seporator regularly even before lite comes on.i had a boost gauge on myn found boost very low which was not good it was limited by wast gate setting. i sold mine rather than endure any further relation ship with the dealer, tho they tried hard, but hard to make honey out of dog ----
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Old 12-31-2007, 08:16 PM
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Quote:
Originally Posted by cliff tate
probly the 2nd worst diesel in the market only toped by the olds joke. i owned from new a gmc withe the 6.5 had 5 fuel pumps in 30000ks. frend who had several in a logging camp had wrist pins fail in 3 out of 6,eventually returning all 6. my neghbor has a 1998 which seems to do ok but it is not worked hard, has lost a trans, i would suggest do not try to take any more power out of yours remove plastic cover and inst cooling kit on fuel injection pump. service the watter seporator regularly even before lite comes on.i had a boost gauge on myn found boost very low which was not good it was limited by wast gate setting. i sold mine rather than endure any further relation ship with the dealer, tho they tried hard, but hard to make honey out of dog ----
Hi Cliff,

I welcome hearing about rough experiences as well - it helps me to keep my eyes and ears open if something does go wrong.

I'll approach this truck the same as my old one because it's the one I wanted - make, model, options wise - and it's paid for as I hate car payments.

If the motor goes out - I'll drop another in, transmission goes...same thing...

I plan on keeping this one until they plant me in a box as I honestly don't prefer any make of newer trucks of this style (crew cab dually 4x4) with the huge plastic bumpers 40-50k+ costs.

I've never paid more than 15k for a car in my life as I'd rather invest my other 35k in another piece of property

In fact if that motor goes out - would anyone recommend going with a newer low mile diesel from 2004-2008?

Any chance they corrected any deficiencies in the motor design?
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Old 12-31-2007, 08:21 PM
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Quote:
Originally Posted by RPM
I would suggest you remove the big plastic cover on the engine and throw it away. Then buy a PMD cooler and install it. The biggest problem with that is that electronic injection pump. It does not like heat at all, and they are notorius for injector pump failures. The biggest thing that fails on the pump is the PMD or Pump Mounted Driver. That is the black box on the side of the injector pump. Get it off the pump and onto a remote mount so it can run cooler. You can buy the cooler on Ebay for about $60.00

http://cgi.ebay.com/ebaymotors/GM-6-...spagenameZWDVW
Curtis - thanks for the great common sense advice, that's a good blueprint to follow.

RPM - it's funny you bring this up - I was wondering about that engine cover functionality anyway and when I was poking around behind the backseat today guess what I found?

I found an old PMD that was recently replaced (11/07)

A cooler is really sounding like a good idea.

Thanks
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Old 01-01-2008, 08:03 AM
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Removing the engine cover and remote mounting the PMD are the biggest things to do. The engines themselves are pretty stout peices. The military has used them and their 6.2 versions for decades,they don't have alot of power but will run forever if maintained well. Trust me soldiers are not easy on equipment I spent 20 years in maint. for the army they beat hell out of em.We used the throttle as an on off switch either wide open or idling.Again the pumps were issues but the relocation kits seem to work well.
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Old 01-01-2008, 09:09 AM
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We ran a 6.5(dealer replaced blown 6.2, but didnt recieve the turbo with the 6.5 so it was n/a) in an 85 4x4,glow plugs were the main issue,about six years ago it blew an oil line(didnt hurt it still turns freely) and Dad swaped it out for a gas engine It got a best of 21.9mpg at 70 mph on a nearly 100 mile each way trip,700-r4 automatic trans and big winch and brushgaurd on the front. I still have the engine and am going to put it in a two wheel drive. In the quest for excellent mpg and still having a little fun.I got another set of pistons the other day that I am going to have machined for 18 to 1 compression so I can run more boost,and pick up more economy(around 10 to 15%)


1973-1974 Chevrolet short stepside
Tonneau cover.
Front air dam.
Rear roll pan.
Lowered around 4/5.
Ton sway bars.
Poly bushings.
Aligned real good.
T-56 6 speed.
Synthetic lube in the rear end.
Small mirrors.
Custom built headers for the turbos(plural ).
GM-8 turbos. may go with one GM-8 and a little turbo off of a daytona or caravan..
3 inch downpipes.
3 inch or 3.5 inch NASCAR boom tubes with x pipe daul exit right under the steps no mufflers for as long as I can get away with it.
Daul front mount intercoolers.
Possibly a cowl hood to let air out of the engine compartment better.
Free flowing air intake to the turbos.
Ported intake or maybe make custom Ram Logs similar to this(which should deliver the best economy).

May go with rear disc brakes.
May do a partial bellypan.
Daul electric fans.
Polish up the exhaust ports a little.
40ish psi in the tires
No A/C (I hate ac in a vehicle..gives me headaches)
And a slick shiney black paint job.

Shane
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Old 01-01-2008, 09:13 AM
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Heres the ad for the 6.2 equally prepped the 6.5s were close on economy.

Shane
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Old 01-01-2008, 09:38 AM
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6.2 re 6.5

Quote:
Originally Posted by barnym17
Removing the engine cover and remote mounting the PMD are the biggest things to do. The engines themselves are pretty stout peices. The military has used them and their 6.2 versions for decades,they don't have alot of power but will run forever if maintained well. Trust me soldiers are not easy on equipment I spent 20 years in maint. for the army they beat hell out of em.We used the throttle as an on off switch either wide open or idling.Again the pumps were issues but the relocation kits seem to work well.
fuel pumps on 6.2s very different, they wher stricktly meckanical pumps, plus being na they produced very little hp, my limited exp. with them was they worked well, in fact the good reports from users prompted me to buy the 1994 6.5ther wer 2 of us who worked for the cat dealer got ours together both wer a disaster.
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Old 01-01-2008, 09:59 AM
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Hmm, the latest Popular Science showed the Duramax 1 ton dually getting only 18 EMPTY with all the new added emissions crap and the new green junk diesel fuel. Dodge Cummins and Ford PS did way worse. Dodge came in at 13 and the Ford at 8!!!! Crap, my old 350 can do that!

Mark
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Old 01-01-2008, 10:34 AM
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Let's face it - you don't buy a truck like this expecting to get fuel mileage and I hate to break it to you guys, I'm not a "greener"...don't really care about mileage ratings much ( other than not wanting to waste fuel by not maintaining the drivetrain properly)

That being said, the truck appears to have a 34 gallon tank - I've got 225 miles with still over 1/2 tank left. When it gets dead center 1/2 tank...I'll fill it up and give you all some numbers for comparison as I at least think the discusion is interesting and informative.
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Old 01-01-2008, 10:38 AM
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Thanks for the PMD relocation advice.

Since the PMD was just replace 11/07/07 ~ I have ordered a heat sink and harness extension for under $100.00 and will put that on as soon as they arrive.

With the harness extension do you think I still need to remove the plastic cover still?
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