Is it possible to roll-start a diesel?

[GreasyJack]

If you’re talking about an older diesel, sometimes you don’t even need a battery at all! I had a friend who grew up on a farm where, among the plethora of old vehicles, was a late 70’s Chevy (I think) diesel pickup that shared its batteries with some other vehicle. During the summer, they didn’t even bother putting the battery back in it-- they had disabled the shutoff solenoid, so they could just roll start it. It wouldn’t have any electrical system, since the alternator wouldn’t work without the battery installed, but it would still drive around just fine since the engine doesn’t require any electricity to run. When they were finished with it, they’d just throw in in 4th and stall it. Of course if you did stall it out somewhere on the spread, you had to trudge back to the barn and get the batteries.

I guess that wouldn’t work with most diesel vehicles, since even most of the older ones have electric fuel pumps, but this one just had a normal mechanical pump that looked suspiciously similar to the fuel pump on gas 350’s.

[Kevbo]

The cam position sensor on a Powerstroke needs up to two full crank revolutions (one full cam revolution) to “home”. Thus while you can push start it, you can’t just “bump” start it like you could a spark engine with a distributer, or a mechanically injected diesel. (Modern distributerless and multiport injection spark engines typically have the same issue).

@Polycarp

If I’m not mistaken – Diesel engineers, please correct me – Rudolf Diesel’s concept was for an engine that would start from heat-of-compression. Glow plugs are useful in heating the fuel to speed up the process, not an essential element of the Diesel engine proper.

It is possible to have high enough compression ratios that this is true. However such high compression ratios put a lot of strain on the piston rings pistons, rods, etc. and also makes a lot of work for the starter (which often requires two batteries even at lower compression ratios) So designers these days design the engines with compression ratios in the 16-25:1 ball park.

In shirt sleeve weather at sea level, most will start fine with no glow plugs, intake heaters, or ether. Cold weather or high altitude, they need some help. I used to spend a lot of time on a Ford Powerstroke message board. Every Fall, you could answer 2/3 of new members’ first post with the words “Replace your glow plug relay”.

Diesel owners in cold climates should carry jumper cables with AWG 2 wire or heavier (smaller AWG number) wire. Note that many discount store cables are as small as AWG 10, which won’t even start a spark engine on a cold day.

BTW: Do NOT use any sort of starting fluid with a modern diesel.

[Deereman]

Ahh, if only you guys could experience the fun of starting an old diesel with a “pony motor” or cranking engine. A small gas engine that it’s only job is to crank and fire up the large diesel. They usually share coolant with the diesel and route the hot exhaust around the diesel air intake, warming everything up. And the fact that the pony won’t die like a battery with extended cranking. You can crank for hours if need be (which you don’t have to, but you could) as long as you keep it full of gas.

The ponies were on the old Deere tractors and Caterpillar dozers. Not since the 1950s though.

I’ve fired 'em up at 20, even at zero, with no problems. No either. Just extended warmup.

[Enola_Straight]

re. the OP:

Yes.

I’ve done it at work with an older VW Golf with mechanical fuel injection.

[dottybaer]

Just wanted to add a little more to this convo, in case it helps.

If your battery is so dead that it cannot fire up the glow plugs enough to warm the ignition chamber, you may have a hard time getting a push start to work, if its gonna work at all.

I say this because of my experience with a non-turbo, direct injection 1985 diesel pickup that wouldn’t start when it got down to -10 degrees F here in Chicago. The battery was also dead. The engine’s cylinders had so much mechanical resistance, due to the air inside them and metal around them being freezing cold, that the piston wouldn’t budge. The truck would come to an immediate, thudding halt when dropping it into first gear, even when going 8 MPH.

Now, might it have worked if I had got going faster? Maybe, but it would have required a more dangerous degree of ‘pushing’ from the car behind me – there are little to no ‘hills’ in this flat city! And, in the city, one doesn’t have the luxury of a long driveway or a virtually empty suburb road to coast along.

I would doubt it would have worked though, given how immediately the truck came to a halt when put into gear (I might as well have been throwing the parking break on!) Didn’t want to wear out any important parts of the engine, so instead I got it close enough to throw a few heating blankets under the hood while the battery was also being recharged. That saved her, but it took 3-4 hours total!!!

In summary, if its warm outside, yes, should work. If its cold outside BUT your glow plugs are still able to come on, then I’d say, it should in theory work. However, if its cold outside and you’ve not no juice to power your glow plugs, then I’d say you’re likely dead in the water…

(If anyone has, on the contrary, had success with that, please post and let us know!)

[beowulff]

Well, this is a bit of a zombie thread, but I figured I’d point out that some (all?) modern diesel engines require some electricity to run. The high-pressure fuel injector is hydraulically pressurized but electrically triggered. If the battery is so dead that the alternator can’t provide some nominal (around 9v) voltage on the main buss, the engine won’t run. For that matter, most modern vehicles require electricity to run the ECM (“computer”), so: no power, no runny.

[vomit_comet]

@dottybaer

I say this because of my experience with a non-turbo, direct injection 1985 diesel pickup that wouldn’t start when it got down to -10 degrees F here in Chicago. The battery was also dead. The engine’s cylinders had so much mechanical resistance, due to the air inside them and metal around them being freezing cold, that the piston wouldn’t budge. The truck would come to an immediate, thudding halt when dropping it into first gear, even when going 8 MPH.

You shouldn’t ever try to bump start any vehicle in first gear. In a lot of heavy duty pickups, first gear is actually lower than a typical 1st gear found in most vehicles and only used while loaded (the truck, not the driver); Second is actually the “no load first” so bumping in first is even more of a no-no in a heavy duty truck. In a normal vehicle bump start in 2nd or third if on gravel or snow, in a heavy duty druck with an extra low first gear; 3rd or even fourth if on gravel or snow.

The reason we park with the vehicle in first or reverse is because the engine compression helps keep the vehicle from rolling down hills, IE, the engine doesn’t turn…, in third or fourth, the vehicle can still roll with clutch engaged depending on the hill and weight of the vehicle.

[bob_2]

@Deereman

Ahh, if only you guys could experience the fun of starting an old diesel with a “pony motor” or cranking engine. A small gas engine that it’s only job is to crank and fire up the large diesel. They usually share coolant with the diesel and route the hot exhaust around the diesel air intake, warming everything up. And the fact that the pony won’t die like a battery with extended cranking. You can crank for hours if need be (which you don’t have to, but you could) as long as you keep it full of gas.

The ponies were on the old Deere tractors and Caterpillar dozers. Not since the 1950s though.

I’ve fired 'em up at 20, even at zero, with no problems. No either. Just extended warmup.

I am no mechanic but have worked around diesel engines a long time. Tractors had many different ways of being started. One was a couple of (what were effectively shotgun) cartridges to get the cylinders moving. Another was a big flywheel which you had to hand crank up to speed, before letting go a clutch and using the energy to start the engine. I believe that the cartridge start was used on aero engines too, as in that old film where they crashed in the desert and a model aeroplane engineer got them to cannibalise the plane.

Trucks were normally started with a battery, and stopped by pulling a cable that shut off the fuel. If you had a truck that was reluctant to start, it was best to park overnight facing down a hill to get a bump start in the morning. On a couple of occasions I helped start a truck engine with a starting handle (remember them?) We wound the engine over a few times to loosen it up and then up to a compression point. With two of us and a rope, we gave a mighty heave and got it running, well, after a few goes we did.

Trucks here generally have 24 volt electrics and two 12 volt batteries. One trick, in extremis only, was to increase the voltage to 36, by adding a slave battery in series. Risky as it could burn the starter motor, but it worked. The engine would keep running, even when the batteries were disconnected to wire them correctly again.

Modern trucks won’t put up with any of this. They have so much electronic stuff on board that jump starting is usually strictly forbidden unless done by a qualified mechanic.

[48Willys]

@dottybaer

Just wanted to add a little more to this convo, in case it helps.

If your battery is so dead that it cannot fire up the glow plugs enough to warm the ignition chamber, you may have a hard time getting a push start to work, if its gonna work at all.

I say this because of my experience with a non-turbo, direct injection 1985 diesel pickup that wouldn’t start when it got down to -10 degrees F here in Chicago. The battery was also dead. The engine’s cylinders had so much mechanical resistance, due to the air inside them and metal around them being freezing cold, that the piston wouldn’t budge. The truck would come to an immediate, thudding halt when dropping it into first gear, even when going 8 MPH.

Now, might it have worked if I had got going faster? Maybe, but it would have required a more dangerous degree of ‘pushing’ from the car behind me – there are little to no ‘hills’ in this flat city! And, in the city, one doesn’t have the luxury of a long driveway or a virtually empty suburb road to coast along.

I would doubt it would have worked though, given how immediately the truck came to a halt when put into gear (I might as well have been throwing the parking break on!) Didn’t want to wear out any important parts of the engine, so instead I got it close enough to throw a few heating blankets under the hood while the battery was also being recharged. That saved her, but it took 3-4 hours total!!!

In summary, if its warm outside, yes, should work. If its cold outside BUT your glow plugs are still able to come on, then I’d say, it should in theory work. However, if its cold outside and you’ve not no juice to power your glow plugs, then I’d say you’re likely dead in the water…

(If anyone has, on the contrary, had success with that, please post and let us know!)

You had one or two problems with your starting method. The first has been adressed, use 2nd or 3rd gear to start any rig, but especially a diesel. The second problem is that on most direct injection diesel engined rigs, there is a fuel shut off relay that needs at least 10 Volts from the battery to turn on the diesel. Since your battery was dead, no relay, & no fuel. You could have dragged it all day in 3rd gear & it still would not have started.

IHTH, 48.

[48Willys]

@Deereman

Ahh, if only you guys could experience the fun of starting an old diesel with a “pony motor” or cranking engine. A small gas engine that it’s only job is to crank and fire up the large diesel. They usually share coolant with the diesel and route the hot exhaust around the diesel air intake, warming everything up. And the fact that the pony won’t die like a battery with extended cranking. You can crank for hours if need be (which you don’t have to, but you could) as long as you keep it full of gas.

The ponies were on the old Deere tractors and Caterpillar dozers. Not since the 1950s though.

I’ve fired 'em up at 20, even at zero, with no problems. No either. Just extended warmup.

I have at least a few times used the pony moter to load a Cat onto the lowboy trailer when the engine needed some serious repairs. One time, the engine was bad enough that the diesel would not start, but it would rotate. Full throttle on the pony motor & low gear on the D-8! Slow but sure. My boss was amazed that I could load it with no help. He expected me to need a LARGE wrecker to winch it onto the lowboy. I half expected to need to use the winch on the Cat to load it on the trailer, but I did not want to load it on backwards, so I tried low gear & it worked!

As far as the OPs question, I do not know about the newer diesels, but the older ones, you bet! I once started my 1980 Diesel VW Rabbit pickup by pull starting it with my motorcycle! Not something that you see everyday, I drew quite a crowd. They cheered when it started. I bought a new battery that day.