I dont have a lot of experiance working on them. I did drive step vans for
a newspaper company part time from that era with the diesels, loaded twice a
week so heavy the rear bumper scrapped going across intersections. I dont
remember any major break downs, head problems,
block failures during that time span, We drove them hard, two
speeds,throttle wide open, or brakes on hard (single copy, newspaper racks,
magizine stands etc)The injectors and injector pumps held up well, the
tranny stayed together(TH400's I believe).They were driven two shifts a day,
some three shifts. Biggest issue I remember was glow plug issues. If the
power steering fluid was kept clean, and power steering fluid not auto trans
fluid used, we didnt have issues with the hydroboost brake system ether.
These were 18 foot step vans.
Thanks for the update.
I found a 94 for $3800 that they say ran good when it was traded in two
months ago. But now something is up with the motor.
They said probably somebody started it too quick before the glow plugs were
warmed up and messed up the injectors.
We will see.
I've never heard of that happening for that reason before on any diesel.
The purpose of the glow plugs is to warm the combustion chamber enough to
ease starting. I am sure you are aware that a diesel is a compression
ignition engine, ie the compression of the air in the cylinder is such that
it raises the cylinder temperature enough to cause the fuel to ignite when
it is injected.
Heavy duty trucks do not have glow plugs because they have even higher
compression ratios than the light duty diesels and as such do not need them.
So I fail to see how a defective glow plug could cause an injector problem.
The biggest causes of injector and injector pump problems are dirty fuel,
and water in the fuel. This is why it is so imperative fuel filters get
replaced on a very regular basis, and the water separator drained, and don't
buy fuel from Joe Blows' Discount Emporium fuel stop. I would walk from
this one unless they repair the issue BEFORE you drive it off the lot.
Besides injector problems because the compression ratios are so high, there
is very little clearance when the piston is TDC if there is a leaky
injector, it could have internal damage from partial hydrostatic lock.
Again, thanks for the info.
That may explain why they said it may need a motor replaced. He fired his
mechanic, and he is not sure what is wrong.
I guess I was wondering if these motors were a remanufactured 305 that GM
made into diesels.
Sounds like they are a different breed.
But you have good advice to walk away from it.
Pardon me for asking, just how high a compression ratio do the "heavy
duty trucks" have anyway? My 6.5L has a stock compression ratio of 21.1
to 1 which is even higher than the Power Stroke or Dodge Cummins.
I was not aware of any diesels that have a higher ratio, and in fact, to
make our 6.5L diesels run better, we install lower compression ratio
pistons, like the one I am building right now at 18 to 1.
I think the reason the heavy duty trucks start easier is the higher pop
pressure on the injectors along with direct injection, but I may be
I worked on 525 Hp Cat powered Transport tractors in the service that had
26:1 compression ratios.
Lowering compression ratios , what they call low compression CI engines are
being looked at hard today. The theroy is lower compression results in
longer burn times, as much as 14 crank degrees longer reducing particle
emmisions, but it also lowers horesepower and torque output as well.
Those rigs I worked on in the service were designed to pull 47-60 ton track
vehicles such as the M-60 tank, the M88 Medium track recovery vehicle, and
the M-1 Abrams tank and that was before trailer and tractor weight was
factored in. They were a vast improvement over the old 10 ton they replaced
as far as pull power was concerned, but then they were replacing 30 year old
The Cummins NT-14+ 435s I drove last were 22:1 compression, the 500+
horsepower models were 24:1
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