300SDL engine seized?
 

The other day I started up my SDL and drove into town -about 4 miles. I noticed smoke coming from under the hood and pulled over. Fuel return line between #4 and #3 injectors ruptured -I found rat chew marks upon later inspection. I luckily found another piece of tubing in my tool box, installed it and drove off. About a mile later the car suddenly slowed -no bad noises or uneven firing -I pulled over and the engine stalled. I figured I must have knocked a fuel line loose so I popped the hood and checked -nothing. I tried re-starting, but the engine cranked very slowly. I noticed it was a little hot, so I let it cool and tried starting again -nothing -barely a crank. I checked charge and connections and found everything fine. I tried manually rotating the engine backwards via the serpentine belt -my breaker was a home -but it would not budge. The engine does not appear to have gotten very hot (I know what that looks like), the oil is fine -no water emulsion, and the coolant is good too. I had the car towed home and there it sits until I can get to it.

Since experience tells me that the broken return line and the engine seizure are most likely related, I am working under the assumption that I have a case of fuel hydrolock, rather than something mechanical. Does anyone here know best how to check for this? This SDL has 394,000 miles on it and has been running like a top nonstop until this happened.

How could a broken fuel return line lead to engine seizure?

Thanks in advance

Pull injectors & see if it will turn over w/ breaker.

It can't.

You had coolant. How hot is a little hot on the gauge?
You had oil. Did you have oil pressure?

Can you turn it over with your breaker bar now?

Clambake,
Welcome to the forum.
By now you will have realized that we are a helpful group & often lightning fast with responses.
It may also have become clear that the more information you put in your post, the better the answer you get.
If you provide the details requested, it will allow much better diagnosis.
It would be interesting to know what else the rat chewed & where it is now.

Good luck with your car.

There is no way you could turn a motor over by pulling on a serpentine belt, it would have to make zero compression to do that, and even then I doubt you could turn it over with your hand on a belt.

Pull the injectors out and see if it turns over with a breaker bar on the balancer.

Thanks for the lightning fast replies!

Ok -so I removed the glow plugs -all bone dry. Starter was still not able to rotate the engine with them out, but I could with my breaker -a little stiff, but I turned it at least one rotation. Does anyone know roughly what torque reading I should have without the glows in?

The temp reached when engine stalled was between 100 and 120 -nothing cataclysmic, but hotter than normal.

Seems like I've had a false alarm, at least as far as the engine is concerned. I'll take the starter out and get it tested -BUT a bad starter does not cause a stalled diesel. Perhaps a large air pocket from the broken fuel return line caused the stall, and a starter saturated in fuel caused the inability to restart?

Any ideas? I would like to know if my hypothesis about the broken return line causing the stall makes any sense -if it does not, I will never know when this problem could resurface.

I sure hope when rotating the engine you were turning it CLOCKWISE and not backwards. The engine's proper rotation is towards the driver side of the car. Never turn it backwards!

I agree with pawoSD, backward rotation is not a good thing. but since you were trying to rotate by hand with the belts, it's unlikely you did much damage there.
I don't see the fuel return lines causing an issue either. with the glows out, all you'd have is ring resistance. rotating the motor by hand with a bar on the crank bolt should not be difficult. possibly 25 foot pounds? your starter could have siezed onto the flywheel, and it could be dragging the motor down though.
how was the oil consumption on your vehicle?

It does sound like air in the system... I don't know in the SDLs, but the SD has a pump on the driver's side of the engine, you can try that if you have it... See if the starter cranks off the car (easy to do with good jump starter cables, just match the + and - poles and do a short touch-and-go)
If it's air, it will eventually start again once you get it out :)

OK -just to clarify -does anyone here believe that a wide-open fuel return line rupture between #3 and #4 can cause an OM603 engine running at freeway speeds to lose power to the point of stalling?

No. Unless it causes you to run out of fuel.

Reading through the post, I am wondering if it is possible that it could be something else...

Not trying to scare up an issue but here is a thought, could it be something else is binding like the IP?

I noticed you said you pulled glow plugs, maybe that doesn't release enough resistance? A previous post had mentioned pulling the injectors rather than the glow plugs. Might just be nit-picking. Also, test your starter and see how many amps its pulling (if you have the equipment to do so.) You could have two separate problems in starting, but that doesn't explain the stalling out.

Example:
 

With the Injectors out of the Head you should be able to turn the Engine
(Clockwise,Facing the Vacuum Pump end of the engine.)
by hand with a 1/4 inch ratchet,easily.

Zomezing,Other than the Fuel Hose (Return type?) breakage is affecting
your engine.

With the Injectors out the engine should spin very fast when driven by the Starter.