Heath Diesel’s 6.5L Diesel Heavy-Duty Cooling System Upgrade

Diesel Articles

6.5L diesel cooling system temperature gauge

The GM 6.5 L diesel truck has a reputation of overheating when towing or hauling heavy and uphill. Those models built prior to 1997 were supplied with a cooling system that, even under the best of circumstances, provided only a marginal performance. Most of these vehicles were not able to maintain coolant temperature at or below the maximum – in my book – allowable 210°F. The normal accumulation of bugs, dirt and crud in the radiator and A/C core made a bad situation worse. Beginning with the ’97 models, GM increased the water pump flow, added a dual thermostat setup and a slightly improved fan clutch in an effort to make things better. These improvements affected a bit of an improvement.

Through years of experience with the 6.5 L diesel, working it hard under towing conditions, Heath Diesel has determined some important and effective remedies for the cooling inadequacies that plague these trucks.

Heath Diesel had long known that retrofitting the ’97 high-output water pump with the dual thermostat onto older models did not provide a meaningful improvement in temperature control and, while we found ways to improve the cooling system performance, the system as a whole did not deliver good and reliable temperature control under tougher towing conditions.


Diesel Articles

efilive-diesel-tuning-injection-quantity-flowchart-featureWhile typical module and program-type boxes allow the user to select something like "Stage 5/150 HP", once you have selected this setting, the module makes all the decisions for you.

In contrast, EFILive’s custom diesel tuning software, on the other hand, allows the user to do something like:

  • Ramp in 70% more fuel
  • Eight pounds of boost
  • 12 degrees of timing in range from 2,800 to 3,500 RPM.

Diesel Articles

Diesel timing tool EFILive Flashscan V2Just about everything you always wanted to know about the variables that affect the timing of your diesel engine; including the relationship between diesel timing and fuel economy.


Das Kommandofahrzeug (6.5L Diesel Suburban Command Vehicle)

Diesel Articles

She hated it... of course she would... It is a real man’s truck: huge, ugly and loud – naturally, it was love at first site for me. I bought it from friends we consider family in Columbus, Ohio. They purchased it brand new on November 24th, 1993 at a downtown dealership for $26,934.72. I knew the truck had a 100% vehicle history, had never-ever been smoked in and if there was any question ever, about anything, it was a phone call away.

The only diesel vehicle I owned before was a VW Lupo 1.4 liter TurboDiesel – the only vehicle that it made any sense to own when you lived in a place like downtown Munich.

Now I live in a metropolis often referred to as Motor City, USA and while a VW Lupo 1.4TD may be hilariously fun, cool and economical; it has no place here. This city with its UAW-dominated parking lots south of the notorious Eight Mile demanded a bullet proof urban assault vehicle that smirks at the potholes big enough to swallow the little Lupo. The Suburban may lack the aramid-kevlar enforced sheet metal and true bullet proof glass of a real urban tank but it makes up for it with a stealth factor that blends into the Detroit surroundings perfectly. So when the owners decided to replace it with a Duramax-equipped Kodiak, I immediately stepped in and gladly adopted the Suburban as my own.

\Nick Buckners 6.5 L Diesel Suburban Das Kommandofahrzeug Nick Buckners 6.5 L Diesel Suburban Das Kommandofahrzeug Nick Buckners 6.5 L Diesel Suburban Das Kommandofahrzeug
Nick Buckners 6.5 L Diesel Suburban Das Kommandofahrzeug Nick Buckners 6.5 L Diesel Suburban Das Kommandofahrzeug Nick Buckner works on his VW Lupo 1.4TD
(Click on any image to enlarge. Suburban photos by Anthony Cressey)


Lube Notes: Gear Lubes and Synthetic Gear Oil


lube-notes_thumbIn this issue of Lube Notes, I will respond to the numerous questions I receive from month to month about gear lubes. From the questions I receive, I realize that folks are not really sure what gear lubes are or exactly why they are different from motor oils. I want to briefly introduce gear lubes and discuss their classification system. Then we will look at proper applications for gear lubes.

First, a little knowledge of gears is important in order to understand the function of gear lubes (please refer to Figure One on the next page for this discussion). Gears transmit motion and power from one rotating shaft to another rotating shaft providing multiple applications of power transmission. There are several types and various geometric shapes for gears but I will only address automotive applications. In Figure One, spur gears, bevel gears and hypoid gears are displayed; sun and planetary gears will be discussed with automatic transmission systems. Spur gears are simple gears with easily meshing gear teeth that transfer power between parallel shafts. Bevel gears allow intersecting shafts to transmit power. Hypoid gears facilitate the transfer of power between non-intersecting shafts at right angles. The important concept to grasp in these gear sets is the action of contact and sliding motion. The spur and bevel gears are engaging and rolling in motion whereas the pinion and ring in the hypoid gears are contacting and sliding. This sliding action allows the Hypoid gears to transmit greater power (the force is distributed over the sliding area), providing for smaller differentials in auto and truck applications.



Revolutions: Gasoline vs Diesel


During the past several weeks, I have had the opportunity to talk with several former diesel truck owners. Each of them had succumbed to last year’s high fuel prices and to a feeling that owning a diesel was simply too expensive – they had swapped their diesel-powered vehicle for a gasoline-powered counterpart. While I empathize with the feeling that something must be done when fuel costs double – a statistic that means thousands of dollars in additional fuel expenses per vehicle even for relatively low mileage drivers – but better to go do something benign, like write your elected officials, than to switch from diesel power to gasoline; at least if the desired result is to save money on fuel as well as on the total cost of ownership (TCO) of your vehicle.

Gasoline vs Diesel

I felt intuitively that diesels are less expensive to own and operate than gasoline-powered vehicles but when I looked at the numbers I was surprised at just how much money could be saved (or lost if you elect to follow the gasoline route). So here is my take on gasoline vs diesel.


Proper Cold Start Performance for 6.5L Diesel Engines

6.2/6.5 Issues and Answers

Well, I am finally admitting defeat; I have exhausted every resource I can think of in trying to solve a problem with my 1994 6.5 liter diesel turbo Chevrolet. It has spent time at five dealerships, eight independent service shops and I don’t know how many different folks have given me opinions on what is wrong. This truck has had a problem getting started in the morning and has since about the time the engine was rebuilt. It starts quickly enough, but then immediately begins to belch smoke, shake and run rough. On the cooler mornings, it will stumble to a stop.


Braking Issue on 2500 6.5L Diesel

6.2/6.5 Issues and Answers

I hope you can help me with a brake problem. The brakes on my 2500 4x4 Suburban pull to the right when I first touch the pedal. It is only a slight tug, it does not feel at all dangerous and it stops straight. However, it wasn’t that way when new, so I know this isn’t right. I have had the front pads replaced and when that didn’t fix it, the shop changed the rotors. When that failed to solve the problem, they changed the rear drums and shoes. They also replaced all of the little springs and things on the shoes to make sure everything is like it is supposed to be. The problem persists. Can you help with any ideas about what to do next? PS We really like the magazine and consider it to be a great investment! Bill J.


Ticking Noise in 1995 K2500 GMC 6.5L Diesel

6.2/6.5 Issues and Answers

If you can help me solve this one, I’ll buy lunch! My ‘95 K2500 GMC has a ticking noise coming from the engine since the shop installed a new A/C pump. I can hear the ticking all the time that the engine is running except when I am coasting at speeds above about 35 MPH. If I let off the throttle at 70 MPH, the noise stops until I get down below about 35, at which point I begin to hear it again. It isn’t just me – everyone who rides in or drives it can hear the same noise. The shop says it is my tappets, that they are gummed up. Another shop guy thinks it is a broken piston. The noise was not there till the A/C repair. Any ideas for me? Remember, I buy lunch! Thanks for the great magazine! Rudy in Norway.


6.5L Diesel Chaos after Engine Computer was Replaced

6.2/6.5 Issues and Answers

I hope you can help me out. I have a big mess on my hands. Recently my ‘98 Chevrolet dually had a transmission shifting problem. I had a reputable shop rebuild the transmission. They also replaced the engine computer, saying it had gone bad at the same time. The transmission seems to be OK but now our truck runs terrible. It starts fine when it has been sitting overnight and it runs OK until it starts warming up. Then, suddenly, it will begin to run lousy and smoke like heck. It is now useless. I can’t drive it because, about the time I get a little ways down the road, it goes bad on me! If I let it sit long enough to cool off completely, it runs fine again for a short time. That shop has spent untold hours trying to fix this problem. Now, after I have spent a truck load of money, the manager of this place has given up and tells me it must be a problem with the wiring and that he does not want it in their shop again. Any help you can offer is greatly appreciated! Desperate in D.C.



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