Diesel World


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I live in north­ern Min­nesota and am look­ing for a pickup truck that can deal with the win­ter cold and still be cheap to drive. Not hav­ing much ex­pe­ri­ence with diesels, I’m in­ter­ested in your opin­ion about an older diesel’s suit­abil­ity for both me and where I live. I’ve read about ex-mil­i­tary diesel pick­ups and SUVS be­ing sold dirt cheap in ve­hi­cle auc­tions all around the coun­try. Some have fewer than 5,000 miles on the odome­ter. Are these ve­hi­cles worth con­sid­er­ing?

Can the ex-mil­i­tary pick­ups be a good choice for a fuel econ­omy ve­hi­cle? What should I look for when eval­u­at­ing one of these diesels at an auction site?

Is the 6.2L diesel a good choice for our cold win­ter cli­mate? Does diesel fuel still gel or clog the fuel sys­tems when it’s re­ally cold? Is the block heater still the only way to go for open-air park­ing dur­ing the win­ter?

My fa­ther owned a Pon­tiac wagon in the late 1970s that was con­verted to use a 6.2L diesel (was orig­i­nally equipped with a 5.7L diesel). That car would de­liver more than 30 mpg on a good day, and was a great car out on the open road.

Vadan Wiess Via Email Aside from be­ing bare-bones trans­porta­tion with few ameni­ties, most ex-mil­i­tary 6.2L diesel pick­ups and SUVS are geared lower (usu­ally 4.10) and come with a 3-speed non-over­drive au­to­matic trans­mis­sion. The low dif­fer­en­tial gear­ing com­bined with no over­drive make these 1980s era trucks hard to live with for to­day’s higher high­way speed lim­its. The first mod­i­fi­ca­tion should be in­stalling an over­drive trans­mis­sion. The best fuel econ­omy will come when the en­gine is run­ning at 1,800-2,000 rpm at your cho­sen cruise speed. De­pend­ing on how fast you drive, this may also re­quire a dif­fer­en­tial gear set change too. For a fuel econ­omy ori­ented 6.2L diesel, I pre­fer 3.42 dif­fer­en­tial gear­ing along with an over­drive trans­mis­sion. It’s not the best choice for haul­ing or tow­ing, but the fuel econ­omy pos­si­bil­i­ties will be what you re­mem­ber from your fa­ther’s Pon­tiac.

A few of the mil­i­tary elec­tri­cal sys­tems are pow­ered by 24 volts DC. These sys­tems in­clude the starter, fuel in­jec­tion pump so­le­noids, and glow sys­tem. I rec­om­mend con­vert­ing these sys­tems to their civil­ian 12 volts DC equiv­a­lents. Re­place­ment parts are eas­ily ob­tain­able, and there’s a lot more tech­ni­cal as­sis­tance avail­able if you need it in the fu­ture. Con­vert­ing to all 12v sys­tems isn’t all that dif­fi­cult.

Not all auc­tions al­low you to start the en­gine or test drive the ve­hi­cle. The bet­ter auc­tions will how­ever of­fer some sort of dec­la­ra­tion in­di­cat­ing what they found dur­ing a pre-auction eval­u­a­tion. Oth­er­wise, just look at ap­pear­ance and whether the ve­hi­cle has been main­tained.

Re­li­able op­er­a­tion of the 6.2L diesel dur­ing the win­ter will re­quire the use of a block heater. I use a block heater on a timer with my 6.2/6.5 diesels when­ever the overnight low dips be­low +20 F. I have the timer set to be­gin a heat­ing cy­cle two hours be­fore I need to drive the truck. Us­ing the block heater al­lows the en­gine to start in­stantly, thus sav­ing wear and tear on the bat­ter­ies and starter. Plus, you be­gin get­ting heat in­side the truck much sooner.

Com­mer­cial diesel fuel is re­gion­ally blended to re­sist cloud­ing dur­ing the cold­est win­ter months. This is ac­com­plished by blend­ing #1 petroleum diesel fuel with #2. Straight sum­mer blend DF2 (diesel fuel #2), un­der just the right con­di­tions of tem­per­a­ture and fuel qual­ity, can de­velop wax crys­tals at ap­prox­i­mately +20°F. These

crys­tals pro­duce a cloudy ap­pear­ance in the fuel, which ac­cu­mu­late in the fuel fil­ter or on the fuel strainer in the fuel tank while the en­gine is run­ning. This ac­cu­mu­la­tion can get to a point of clos­ing off the fuel sup­ply to the en­gine, and the en­gine will stop run­ning. Win­ter­ized #2 diesel fuel is sup­posed to re­sist cloud­ing down to the low­est tem­per­a­ture ex­pected in a given re­gion, but fuel blend­ing is done weeks in ad­vance and might not be ad­e­quate for a big un­ex­pected drop in tem­per­a­ture. As a pre­cau­tion, all diesel own­ers can treat their own fuel dur­ing pe­ri­ods of ex­tremely low tem­per­a­tures if you don’t com­pletely trust the win­ter­ized fuel blend­ing at the pump. Most na­tional brand fuel treat­ments can help diesel fuel re­sist cloud­ing and gelling. As of the spring of 2017, I’ve driven a diesel pickup through a to­tal of 31 cold Mon­tana win­ters, and have never once ex­pe­ri­enced gelled fuel. Good luck with your truck.

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