Hidden Time Bomb Truck Engines of the 1960s-70s
Remember when you could actually work on your own truck without needing a computer degree?
The 1960s and 1970s were a different time for American trucking.
These were the glory days, or so we thought.
Chrome bumpers, steel dashboards, and engines you could rebuild in your driveway with a basic socket set and a six-pack.
But here is the thing nobody talks about enough.
Some of those engines that powered America’s highways were ticking time bombs.
Beautiful to look at.
Sure.
Powerful.
Absolutely.
Reliable.
Well, that is what we are here to discuss today.
I am talking about engines that looked great on the dealer’s lot, but left drivers stranded on lonely highways.
Power plants that mechanics learned to dread.
The ones that made grown men who had driven a million miles question their choice of career.
Let’s start with one that will get some of you fired up.
The Detroit Diesel 8V71.
Now, before the comment section explodes, let me say this.
The 8V71 had its fans.
Plenty of drivers swore by it, but just as many swore ate it, and with good reason.
Detroit Diesel introduced the V71 series in the late 1950s, and by the 60s and 70s, these two-stroke diesels were everywhere.
The 8V71 was the 8-cylinder version, and it powered everything from highway tractors to Greyhound buses.
You could hear one coming from a mile away.
That distinctive screaming wine of the supercharger was unmistakable.
Here is what made it problematic.
This engine was a fuel hog that made your wallet cry.
We are talking 4 to 5 mp gallon if you were lucky.
When diesel was cheap, guys tolerated it.
But when the oil crisis hit in 1973, running an 8V71 became financially devastating.
The cylinder liner problems were legendary.
These engines used wet liners that could crack or shift, and when they did, you would have coolant mixing with your oil.
You would see that telltale chocolate milk on the dipstick and know you were in for an expensive rebuild.
But here is the real killer, the blower itself.
That roots style supercharger needed regular maintenance and when it failed, when the rotors scored or the seals wore, you were looking at a roadside breakdown.
I have talked to old-timers who said they carried spare blower oil in their toolbox because these things went through it.
The 8V71 was not all bad.
It made good power, around 318 horsepower in highway tune, and it would run forever if you maintained it religiously.
The problem was that religiously meant constantly.
Now let us talk about an engine that broke a lot of hearts.
The Cumins V903.
Cumins was and still is a legendary name in diesel engines.
But even the best companies have their missteps and the V903 was one of them.
On paper, it looked great.
In the real world, it was a different story.
The first major issue was head gasket failures.
The V903 used individual cylinder heads, eight of them.
And those head gaskets were under tremendous stress.
The engine ran hot and those gaskets would blow with disturbing regularity.
You would be cruising down the highway and suddenly you would see steam billowing from under the hood.
Replacing one head gasket was bad enough.
But here is the thing.
When one went, the others were usually not far behind.
Smart mechanics learned to replace all eight while they were in there.
Turning a bad job into a nightmare job.
The cooling system was chronically inadequate.
Cumins struggled to get coolant flow right in the V configuration and hot spots would develop.
This led to warped heads, cracked heads, and more blown gaskets.
Drivers learned to watch their temperature gauges like hawks.
Cummins kept trying to improve the V903 throughout its production run, which lasted into the early 1980s.
They made changes to the cooling system, strengthened components, improved the head gasket design, but the fundamental issues remained, and the engine never really escaped its reputation.
Now we come to an engine that will upset some Mac loyalists.
The Thermodyine 673.
Mac trucks have always had a devoted following.
The phrase built like a Mac truck was not just marketing.
It was the truth.
But even Mac had its troubled children.
The end 673 thermodyine was one of them.
This was an inline sixcylinder diesel displacing 673 cub in.
Mac put them in everything from R models to DM models throughout the 1960s and ‘7s.
The Thermodine name came from the direct combustion chamber design which was supposed to provide better fuel economy and cleaner combustion.
The theory was great.
The reality was problematic.
The biggest issue with the 673 was the cylinder head.
Mac used an overhead valve design with the injectors mounted vertically in the head, and that head ran hot.
The combustion chambers were directly in the piston, which meant high heat concentration.
Those heads would crack, especially between the valves.
Mechanics said they could spot a 673 that was about to crack ahead.
The engine would start using coolant just a little at first.
You would top off the overflow tank every few days.
Then it would get worse and worse until finally you would lose the head gasket or crack the head itself.
The fuel system on the 673 was another adventure.
Mac used American Bosch injectors and pumps and they were finicky.
The injector timing had to be precise.
If it was not, the engine would either knock like a bucket of bolts or lose so much power you could not pull a loaded trailer up a grade.
The valve train was another weak spot.
The 673 used adjustable rocker arms and they needed constant attention.
The oil consumption was legendary.
Break one in wrong or let it get hot and it would start using oil.
This was not a quart every few thousand miles.
This was a quart every few hundred miles.
Matt kept improving the 673 and later versions were better.
The E6 series that came later was actually pretty decent.
But those early and mid-production 673s gave more than a few drivers gray hair.
When a 673 was running right, it was a good engine.
It made decent power, up to 237 horsepower, had good low-end torque, and that distinctive max sound was music to a true truck driver’s ears.
But keeping one running right required dedication, deep pockets, or both.
If you’re enjoying this trip down memory lane, or if this is bringing back some expensive memories, make sure you’re subscribed.
We have more troubled engines to cover and you won’t want to miss what’s coming next.
Let’s shift gears and talk about Caterpillar’s entry into highway truck engines.
The 1693 Caterpillar was the king of off-road engines for construction equipment, mining trucks, and generators.
Those CAT engines would run forever in bulldozers, and excavators.
So when they decided to get into the highway truck market in the late 1960s, everyone assumed they would dominate.
The 1693 was an inline 6-cylinder turbocharged diesel, displacing 1,693 in.
That’s over 27 L.
This was a big engine based on CAT’s successful industrial engine platform.
Here is the problem.
What works in a bulldozer does not necessarily work in a highway truck.
The 1693 was tough, almost indestructible really.
You could abuse it, neglect it, and it would keep running.
But it had serious drawbacks that made it unpopular with over the road drivers.
First, it was heavy.
We are talking over 4,000 lb.
That is weight you are hauling around that is not cargo, which meant less payload.
In an industry where every pound matters, that was a significant disadvantage.
Second, it was a fuel hog.
The 1693 was designed for constant load applications, not the variable conditions of highway driving.
It would drink diesel like there was no tomorrow, managing maybe 4 m per gallon if you were gentle with it.
When the 1973 oil crisis hit and diesel prices shot up, operators running 1693s felt it in their wallets.
Third, and this is where it really became a problem, the turbocharger system was troublesome.
CAT used a fixed geometry turbo that was great for steadystate operation, but struggled with the constant speed changes of highway driving.
Those turbos would fail, and when they did, you lost so much power that the truck became nearly undrivable.
Maintenance on a 1693 was an event.
Everything was big and heavy.
Changing injectors required special pullers.
Adjusting valves took forever because of the size of everything.
An oil change took 10 to 12 gallons of oil.
This was not an engine you maintained in your driveway.
You needed a proper shop.
The cooling system had its issues, too.
That big engine generated tremendous heat, and the radiator and coolant system had to be sized accordingly.
Overheating was a common problem, especially in hot climates or when pulling heavy loads up long grades.
Interestingly, the 1693 found a second life in marine and industrial applications where its durability and simple design were advantages rather than drawbacks.
But for highway trucking, it was the wrong engine at the wrong time.
We can’t talk about problematic engines without mentioning International Harvesters DVT573.
International Harvester was a major player in the truck market during the 1960s and the 1970s.
Their trucks were everywhere.
Loadars, Transstars, and COF models.
And many of them were powered by the DVT573.
DVT stood for direct vertical turbocharged which sounded impressive.
It was a V8 diesel displacing 573 cub in and IH marketed it as a modern efficient power plant for medium and heavyduty applications.
The reality was less impressive.
The DVT573 had a fundamental design flaw.
It couldn’t keep its head gaskets sealed.
This was an endemic problem that international harvester never fully solved.
The V configuration combined with high cylinder pressures from the turbocharger put enormous stress on those head gaskets.
You would be driving along and suddenly you’d notice the temperature climbing.
Pull over, pop the hood, and there it was, coolant weeping from between the head and the block.
If you were lucky, you caught it early.
If not, you would blow the gasket completely and be looking at a tow truck.
The turbocharger setup was problematic, too.
IH used their own turbo design and it was not robust.
The bearing would fail, the wastegate would stick or the compressor wheel would rub.
When the turbo failed, parts were expensive and often on back order.
The fuel injection pump supplied by Rousa Master was sensitive to fuel quality.
Get some bad diesel or a batch with water in it and that pump would start acting up.
It would lose prime, cause rough running or fail completely.
And unlike some other engines where you could limp home with a bad pump, the DVT573 would just quit.
Oil consumption was another issue.
These engines would start using oil, and once they started, it was hard to stop.
Ring wear, valve guide wear, turbo seal leaks, all contributed to the problem.
Drivers learned to carry extra oil, and mechanics learned to recommend rebuilds long before the engines actually failed.
International Harvester eventually replaced the DVT573 with the DT466 and other engines which were far better.
But for the years the DVT573 was in production, it gave International Harvester a black eye in the marketplace.
Fleet managers learned to avoid trucks with that engine and resale value suffered accordingly.
So there you have it.
Five engines from the 1960s and the 1970s that were hidden time bombs.
The Detroit Diesel 8571 with its constant maintenance needs.
The Cumins 5903 with its head gasket failures.
The Mac Thermodine 673 with cracking heads and heavy oil consumption.
The Caterpillar 1693 which was too heavy and thirsty for highway use.
And the International Harvester DVT573 which just could not keep its gaskets sealed.
Now, here is the important thing to remember.
These engines were not total failures.
Each one powered thousands of trucks and kept America’s freight moving.
Many operators ran them successfully for hundreds of thousands of miles.
But they all had issues that tested the patience and the wallets of the people who had to live with them.
If you lived through this era, you have stories about these engines.
Maybe you drove a truck with one.
Maybe you wrenched on them for a living.
Maybe you owned a fleet and had to decide whether to rebuild or replace.
Those experiences shaped the industry we have today.
