1997 GMC Suburban 1500 LE 6.5 Turbo Diesel

Before using biodiesel in a Chevy or GMC 6.5 Turbo Diesel, there are a few things you should know and some potential modifications you should make to your vehicle.

Get to Know Your Vehicle before Running Biodiesel

If this is a used vehicle, drive it first and get all of the maintenance done.  Resolve any technical problems and make sure you are comfortable with the condition of the vehicle first.  If you rush into converting over to biodiesel without getting it into perfect condition, you might mistake a normal technical issue with a problem related to biodiesel.

Here is a list of some modifications I made to my ’97 GMC Suburban to improve performance and reliability before preparing it for biodiesel use.

Relocating the PMD

The injection pump controller (PMD) is mounted on the side of the injection pump in the valley of the engine. It is susceptible to heat and fails often on this motor. This is the cause of most injection pump problems. There are kits that relocate the PMD to a heat sync with an extension down to the bottom front of the engine where air will blow over the unit keeping it cool. This mod is highly recommended. (especially if you plan on running an SVO kit)  I purchased the Heath Diesel PMD Isolator for my Suburban.  Make sure you choose the correct model.  There are different versions depending on if your vehicle is 2wd or 4wd.

Replacing the Stock Fuel Lift Pump

The stock fuel lift pump on the 6.5 diesel is weak and often is ready for replacement around 100k miles.  Replace it with an aftermarket Heavy Duty lift pump.  I purchased one online from Heath diesel here.   Heath Diesel is a great resource for improved parts for the 6.2 and 6.5 turbo diesel engines. When you do this, make sure the o-rings are viton.

Cleaning and Securing Ground Connections

If you are having electrical problems with weird behavior, it is likely the result of a bad ground connection. Removing ground connections, cleaning them with steel wool and reinstalling should help.

Eliminating the Stock Vacuum-Actuated Turbo Wastegate Controller

The waste gate controller is vacuum driven and this is the only use of the vacuum pump. (brakes are hydraulic) Most owners that plan on keeping the vehicle long term replace this with a spring-actuated wastegate. I used a Turbo-Master spring-actuated wastegate  controller and eliminated the vacuum pump with a smaller serpentine belt. This is an easy mod and the parts and instructions are available online.

Once the truck is running well and you are familiar with its driving behavior, upgrade the fuel system and start running biodiesel.  Having a good baseline knowledge of your truck’s behavior will help you with troubleshooting future issues that may not be related to biofuels.

Replacing the seals in the Fuel Manager

The fuel filter housing was not built with viton o-rings and seals.  Remove it from the truck and rebuild it with all viton o-rings and seals. There are o-rings on both the water sensor and fuel heater as well as the fuel filter seal for the fuel manager cap.

Replacing the fuel hoses with Biodiesel-Resistant hose

There are several soft hoses in the fuel system that need to be replaced before running biodiesel.

• 5/16″ID fuel hose from steel supply line to the rear of fuel manager
• 1/4″ID fuel hose from fuel manager to supply on the injection pump.  This runs under the intake manifold.  You can replace it without removing the manifold by taping the new hose to the end of the old and pulling it through.
• 1/4″ID fuel hose jumper from steel return line to the injection pump.  This one is also under the intake manifold and can be replaced without removing the manifold using the method above.
• 1/4″ID fuel hose from fuel manager to fuel/water draincock at front of engine.  This one also runs under the intake manifold and can be replaced with the method listed above.
• 1/4″ID fuel hose from fuel/water draincock to open end.
• Don’t forget the 1/4″ID small u-shaped jumper hose at the front of the engine behind the serpentine belt tensioner.  I missed this one and had a pesky air leak here in my fuel line that took me forever to troubleshoot!

I used the stock GM hoses for the first 20,000 miles of running biodiesel and ended up with hoses looking like this.  (I used mostly B100)  They ended up sucking air into the fuel system and causing the truck to blow white smoke and stall.  I recommend updating the hoses before running biodiesel of any blend so you don’t have to deal with a stall or towing bill.

Recommended Replacement Hoses

Here are some of the 1/4″ replacement viton-lined hoses that are biodiesel compatible.  You have the right stuff if you see “SAE30R9″ printed on the hose.  (SAE30R5 or SAE30R7 will not work and will rot)

These updates should keep you on the road running biodiesel in your GM 6.5 Turbo Diesel.  They are not the most reliable diesels on the road but can be kept running with proper troubleshooting and some DIY mechanical knowledge.

Addendum: Running a GM 6.5 Turbo Diesel on Waste Vegetable Oil

Frybrid makes a computer-controlled Straight Vegetable Oil (SVO) kit with custom aluminum tank. The Chevy 6.5 diesel motor has indirect-injection so it is adapted well to vegetable oil. However, make sure that you relocate the PMD before you start running heated oil through the injection pump. Otherwise, this will fail and need replacement.

Frybrid SVO Kit for the GMC 6.5 Suburban

Most SVO kits that provide proper heating of the VO fuel should work fine with the 6.5 turbodiesel. The VO fuel should be at 160*F for proper combustion. At this temperature, most VO is at the same viscosity as No.2 diesel. Make sure that you take proper care when tapping into the stock fuel system to reduce the possibility of introduction of air into the system. Improper heating and air in the fuel lines are the most common problems with SVO installations.

Properly preparing the vegetable oil for burning as a fuel is important. Make sure to research how to remove impurities and water from the oil before using it as fuel. It is critical to proper combustion and preventing clogged fuel systems.

Montero Diesel Conversion

Making the choice to run biodiesel in your car can be difficult for the average driver.  As we all know, almost all passenger vehicles run on gasoline in the United States. There are very few diesel-powered cars such as the Volkswagen/Audi TDIs and Mercedes diesels, so most consumers that want to run biodiesel end up driving a large pickup truck like a Ford F250 or Chevy Duramax.

One option that is interesting to me is converting a car to diesel power. Is this difficult? How can it be done? How will I get a license tag and title for a diesel conversion? These are a few of the questions that came to my mind when I first considered the project. I decided a few years ago to embark on a research project to convert a gas car to diesel to see how it could be done.

This is the first of a series of blog posts where I will document my conversion of a 1987 Mitsubishi Montero from a 4 cylinder 2.6 liter gas engine to a 4 cylinder 2.3 liter turbo diesel engine.  Stay tuned… this should be a fun ride!

Since I advertise my use of biodiesel with bumper stickers, I’m often asked about what new vehicles are good for running biodiesel.  For this reason, I’ve done some research on new diesel cars and trucks and what I’ve found is disturbing for the biofuel movement.  Since about 2006, the Volkswagen diesels will only warrant biodiesel at a blend of B5.  I would hardly even call that biodiesel since it is really only using it as an additive.

From what I’ve read on forums of real biodiesel users, this limit is for good reason.  The electronics that control fuel flow and injection on the newer diesel engines don’t appear to be designed to run anything except for petroleum-based diesel.  According to some experts, the minor differences in viscosity and cetane rating cause problems for the newer engines and can lead to mechanical issues.

The new BMW 335d diesel here in the US also only warrants up to B5 in their diesel engine.  Experts on the BMW forums indicate that the BMW diesel uses a high pressure injection system similar to the VW TDI and will have trouble injecting biodiesel blends greater than B5.  Higher blends contaminate the oil requiring much more frequent oil changes.  They can also cause problems for the emission systems.

As US manufacturers begin offering domestic diesel cars, we need to make sure they use fuel systems compatible with at least B20 blends of biodiesel.  If this issue concerns you as well, reach out to the manufacturers and ask them to engineer support of bioidesel into their engines.  GM just announced yesterday they will bring the Chevy Cruze diesel to the US so let’s start with them and tell them we want biodiesel-compatible diesels here!

For now, it looks like I’ll need to continue maintaining my older VW diesels to preserve them for the future.

Diesel Fuel
Diesel fuel is made from petroleum and is a very efficient and energy dense fuel when used in a compression ignition engine. (diesel) It takes less energy to crack petroleum into diesel fuel than it takes to make gasoline. It also burns more efficiently in a diesel engine more miles to be traveled per gallon and producing less heat.

Biodiesel Fuel
Biodiesel is another form of diesel fuel that is made from plant oils or animal fats instead of petroleum. I run several of my personal vehicles on biodiesel including VW TDIs, a Dodge RAM and a Ford Excursion.  In order to make the oils or fats close to the same consistency as diesel fuel, it is chemically modified using an alcohol as an additional reactant and a catalyst. Typically, the alcohol reactant is methanol and the catalyst is Sodium Hydroxide or Potassium Hydroxide.

Manufacturing Process
The oil is heated to facilitate the reaction. The alcohol and catalyst are mixed together and mixed into the oil causing a chemical reaction called transesterification. Transesterification creates biodiesel fuel and a waste product called glycerine. After the reaction, the glycerine separates from the biodiesel and drops to the bottom of the reaction vessel. The biodiesel is removed, washed and dried before using it in a vehicle as fuel.

Naming Convention
Biodiesel is used in several different ways and there is a naming system to identify its type. In its purest form, biodiesel can be used without dilution direct in a diesel engine. When it is used as 100% biodiesel with no diesel mixed in, it is called B100. (‘B’ for Biodiesel and ’100′ for 100%) The more common way to use biodiesel is to dilute it with diesel fuel in several different ratios. B20 is a mixture of 20% biodiesel and 80% diesel. B50 is a mixture of 50% biodiesel and 50% diesel.

Diesel Fuel Additive
When the dilution of biodiesel drops below 10% it is usually considered to be a fuel additive similar to the way ethanol is used as a 5% additive in gasoline. B5 is the most commonly used dilution for a diesel fuel additive. 5% biodiesel and 95% diesel.

Waste Vegetable Oil
Waste Vegetable Oil or WVO can be used directly in a diesel engine by using heat to reduce the viscosity of the oil to make it closer to the consistency of diesel fuel. (Straight Vegetable Oil (SVO) can also be used in the same method described here. It is just unused vegetable oil so it is not a waste-stream-based product) Reducing the consistency allows it to flow in the fuel lines and combust properly in a diesel engine. For this to work, the fuel system on the diesel vehicle must be modified to heat the oil before combustion. Typically, WVO at temperatures of approximately 160 degrees Fahrenheit is the same consistency as diesel fuel.  I have personally run a Ford Ranger and a Mercedes on two tank WVO fuel systems.

Heat Source
Systems either use waste heat from the the engine to heat the fuel or an electric heater run off of the electrical system in the vehicle. In the case of the waste engine heat system, the vehicle is started on regular diesel and then switched to WVO once the vehicle is up to operating temperature. (typically 180-210 degrees Fahrenheit)

Two Tank Systems
The system described above for heating the fuel is typically used with a separate tank for diesel fuel and another tank for WVO. A switch mechanism is used to change the tank source once the vehicle is at operating temperature or the electric heat source has heated the fuel to the proper temperature.

One Tank Systems
There is a practice that some drivers use that leverages a one-tank system for WVO. Instead of relying solely on heat to reduce the viscosity of the oil, they mix it with diesel and/or regular unleaded gasoline (RUG) to thin out the oil. They pour the mixture into the single stock tank of the vehicle and run it in this manner. The one-tank method can be problematic in colder weather and since proper dilution of the oil can be difficult to maintain if the fuel is blended in the tank itself.

I hope this helps you with understanding the differences in the types of diesel fuel

The goal of this site is to share both experiences I’ve had in the biodiesel industry and to report on current news related to the biodiesel industry.  I hope that you will find this site informative and will share it with others.  We also encourage feedback on our posts via our comments section.

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- Veggie Ranger