How to Convert a Chevy GMC 6.5 Turbodiesel to Biodiesel

Diesel Suburban

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!

stock hoses after running biodiesel

stock hoses after running biodiesel

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

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

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.

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9 Responses to How to Convert a Chevy GMC 6.5 Turbodiesel to Biodiesel

  1. excellent info,any mods inside the injection pump,will a pump off a turbo work on non turbo(6.5)

  2. excellent article,what is differance between turbo and non turbo injection pump,thanks dave

    • horatio says:

      i wrote a question on this site…..please read it and let me know………im much embladged!!!!!!!!!!!im horatio.if i can get number to call you even better……im in be calling you… you dont have to spend you minutes!!!!!!!!!!!!!!!!!!!!

  3. horatio says:

    thanks alot………big help…….need a place where to get the system…and about how much are we talking about.apreciate it much.and yes tell me what other engine will be better off then 6.5 turbo diesel……..maybe a 6.2????????????let me know asap……….thanks…… im bidding off on a 86 sierra with a diesel engine…on the 4 of febuary.

  4. Bill says:

    Can you give the same detailed instructions for replacing fuel line hoses for a 6.2 litre engine (1987 Suburban)? Thanks.

    • psmith says:

      Hi Bill,

      Unfortunately, I’ve never looked under the hood of a 1987 diesel Suburban. I wish I could help you. Try one of the Chevy Diesel forums. They are very helpful.

  5. Pingback: Biodiesel Times

  6. Well done PSmith! I have been looking for a conversion manual for my old Suburban and you make it look too easy my friend. Time to turn the old farm rig into a bio-beast:)

  7. Matthew McCleary says:

    Are you sure the wastegate is the only thing that operates on vacuum? Typically, heater blend doors, cruise control, and other things work off vacuum too.

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