Starting/preheating a Caterpillar 3208

With our Cummins engines (circa 1989), you turned the key to On and watched the tachometer, when it pegged and then returned to zero, the engines were preheated and ready to start.

With our Volvos (circa 1999), you turned the key to On and waited for the diagnostic light to go out.

The Yanmars (circa 2004) had no visual indicator; you just turned the key to On and counted to ten before starting.

How do you tell when a 3208 engine is preheated and ready to start?

Turn the key and go

We came from 5.9 Cummins with the air heater (turn the key, wait while the toasters drain the batteries, then start)...with the Cat 3208TA engines we have now, it had always been simply turn the key and the engines start, as there are no preheaters.

This is year round, including during a prolonged cold spell down into the teens. I let the engines idle about 2 minutes before we leave port.

3208s don't seem to need pre-heating. Mine don't have it and don't need it. They fire right up as soon as the starter begins to spin.


Edit: This even after sitting on the hard in the broker's yard for almost a year.

Okey-dokey. Easy enough. Thanks.

Yep, no preheat on a 3208. Direct injection, no glow plugs, no air heater. Hit start and go.

My 3208TAs start instantly when cold too. It's actually quite impressive. I don't think they make it past half a revolution on the starter, even at 40 degrees F. My marina neighbor is a high performance diesel builder (he builds pulling tractors) and he said it's all about the injection timing. His 1000+ HP pulling tractor engines are really hard to start due to the aggressive injection timing. I wish my Kubota engine on my Onan genset started as easily as my CATs.

We had our NT on the hard in Connecticut for the winter for 5 months after we purchased it. After the Marina splashed it we turned the key for the first time since the sea trail 6 months or more prior
The 3208t fired up so fast it scared us, as it did every morning for the whole trip home.

They say nothing runs like a Deere, well nothing starts like a Cat.

Mischief Managed said:

I wish my Kubota engine on my Onan genset started as easily as my CATs.

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Interesting. My experience with Kubota engines is that they always start right up, even if sub-zero F temps. Definitely gotta run the glow plugs, but then they start right up.

twistedtree said:

Interesting. My experience with Kubota engines is that they always start right up, even if sub-zero F temps. Definitely gotta run the glow plugs, but then they start rightt up.

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My neighbor has a Kubota tractor with basically the same engine as my genset, and it starts just fine after using the glow plugs, even at really low temperatures like -20F. That got me thinking about the differences between the two engines, and I came up with the following theory:

I suspect it's the governor on my genset that makes it start without vigor. When you start a non-governed diesel, the throttle is typically set to idle, which means very little fuel is going in. As long as there's enough heat in the combustion chamber to ignite the fuel going in, it will start right up, just as my CATs do. On a mechanically-governed engine, the throttle is wide open when the engine is off because it's trying to achieve 1800 RPM and it's clearly not any where near 1800 RPM. Thus, when I try to start it, the maximum amount of fuel possible is going in, which cools the combustion chambers and makes it harder to start. I bet if I held the throttle at idle while cranking the engine over, it would start immediately, like my neighbor's tractor. Another thought I have is that the engine may not have any variability to the injection timing since it's designed to run at 1800 RPM only. That would likely mean that the injection timing is too advanced at low speed which would exacerbate the issue by spraying fuel into the combustion chamber before it even reaches it's highest temperature.

If it's mechanical injection, you could try holding the injection rack back while starting to see if that makes it start more easily.

Mischief Managed said:

My neighbor has a Kubota tractor with basically the same engine as my genset, and it starts just fine after using the glow plugs, even at really low temperatures like -20F. That got me thinking about the differences between the two engines, and I came up with the following theory:

I suspect it's the governor on my genset that makes it start without vigor. When you start a non-governed diesel, the throttle is typically set to idle, which means very little fuel is going in. As long as there's enough heat in the combustion chamber to ignite the fuel going in, it will start right up, just as my CATs do. On a mechanically-governed engine, the throttle is wide open when the engine is off because it's trying to achieve 1800 RPM and it's clearly not any where near 1800 RPM. Thus, when I try to start it, the maximum amount of fuel possible is going in, which cools the combustion chambers and makes it harder to start. I bet if I held the throttle at idle while cranking the engine over, it would start immediately, like my neighbor's tractor. Another thought I have is that the engine may not have any variability to the injection timing since it's designed to run at 1800 RPM only. That would likely mean that the injection timing is too advanced at low speed which would exacerbate the issue by spraying fuel into the combustion chamber before it even reaches it's highest temperature.

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No. The Kubota and most small diesels are indirect injection (IDI), larger engines like the Cat are direct injection (DI). DI has the injector squirt right into a bowl on the piston, the bowl forms the combustion chamber. IDI has a combustion chamber in the head, ported to the cylinder. The injector squirts into that chamber (also called a pre chamber or swirl chamber), then the burning gasses flow into the cylinder.

When starting an IDI engine, lots of heat of compression is lost as the hot gasses squirt through the cold metal and into the chamber. That is why almost all IDI engines need some glow plug heat (also in the chamber) to get enough heat to fire.

IDI is used to reduce combustion noise, but there is a penalty in efficiency. On larger engines DI is preferred as efficiency is primary and noise concerns secondary.

DI engines don't need preheating, but there will be a temperature below which they simply do not start. Some Cummins, Yanmar, etc models have an electric grid heater in the intake manifold to help cold starts, but in the marine world how many are boating in zero deg F weather?? The grid heater also reduces cold idle smoke. Many boaters find the grid heaters annoying and disable them. Hard on the rest of the electrical system.

Some automotive DI engines have glow plugs that extend the tips into the piston bowl combustion chamber, but I don't think they are in the marine world.

The governors on DI and IDI engines basically act the same way, with some tuning differences and a wide variety of mechanical gizmos to make it work. But the basic control of the injection by the governors of any type act similar.

As others have said, all you need to do is show a 3208 a starter motor and it will jump into life!

ManagedMischief, I wonder if your glow plugs are operating correctly. I had a circa 2008 Onan with Kubota engine and as I recall the start sequence was automated by the control panel. You would push the start button and walk away, then 10-15 sec later the unit would start after running through a pre-heat cycle.


Does yours work the same way, or is it manual like starting your neighbor's tractor where you need to activate and hold the pre-heat for some amount of time, then crank to start?

Most IDI engines like Kubota need about 5-10sec of glow plug preheat in normal boating temps. Maybe longer if cold. If it does not start right away, give up and give it more preheat.

Any Kubota that is hard to start with preheat, you need to check out the glow plugs and their power supply.

twistedtree said:

ManagedMischief, I wonder if your glow plugs are operating correctly. I had a circa 2008 Onan with Kubota engine and as I recall the start sequence was automated by the control panel. You would push the start button and walk away, then 10-15 sec later the unit would start after running through a pre-heat cycle.


Does yours work the same way, or is it manual like starting your neighbor's tractor where you need to activate and hold the pre-heat for some amount of time, then crank to start?

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Mine is 1992 vintage and the glow plugs are totally manual. If it does not start right away, I just run the glow plugs another 10 seconds and it start fine, but it never bursts to life like my CATs.



I bought my boat from the third owner (who only owned the boat a year and put 6 hours on it), but the second owner is the one that owned it the longest and used it the most. He and I have been communicating extensively about the boat since before I actually closed the deal to purchase it. He was well aware of when we were taking possession of the boat to cruise it 1000 nautical miles home and texted me on morning of day two just to say "in the morning, it almost gives you a woody when those diesels jump to life, eh?" He was spot on. I was in touch with the third owner recently for the first time (I bought the boat long distance through a broker so I never met or spoke with the guy that sold it me) and he said his favorite memory of the boat was the way the engines started so effortlessly.

Love our 3208 Cats

Like so many other happy Cat owners, or 1989 Cats have always started immediately, push the botton and no hesitation, boom they are running. Love them. 7500 hours and oil samples are excellent.

I’m sorry to see the 3208 go away. It was a very good engine when not over HP’ed . Thanks Ski for the lesson, good info right there.

My Perkins has some sort of diesel flame pre-heat system that is not connected on my boat. It starts right up down to 38 degF without it just fine, thank goodness!

The Perkins (most anyway) preheat is an (feeble) attempt to get some latent diesel hot enough so that it doesn't leave a sheen or smoke at startup. Most will fire right up without giving it that 10 second count.

Yup.. below freezing or not run in months it doesn't matter - if I ever actually hear my 3208 cranking I'll know there is something wrong!

tiltrider1 said:

They say nothing runs like a Deere, well nothing starts like a Cat.

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I used to run a Cat 977 track loader. In the midwest winters, I would hit the glow plugs for 60 seconds, wait another 60 seconds and repeat. I'd then crank the engine with throttle closed for a few seconds and then crack the throttle. At first, just vaporized fuel out of the stack, and then an occasional hit, then a few more and eventually it would catch.

For the first 15 mins or so, it would hardly move with cold transmission, but eventually it would warm up and you could then move normally.

Upon starting, it would take the turbo a minute or two before it started spinning.