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Recently, a squirrel paid a visit to the engine compartment of my 1999 VW (it's a diesel 1.9 TDI). Besides leaving some crabapples as gifts, it chewed clean through one of the fuel injector return hoses. I didn't discover it until reaching my destination and smelling/observing the spilled diesel which was bathing the front of the engine. I did not start the car until I tracked down a piece of replacement hose (not easy due to the location and the fact it was a holiday evening).

Could I have plugged or otherwise sealed the ends of the cut hose and driven home without doing any damage?

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  • And all I thought squirrels were good for was to distract ya! :o)
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Aug 8, 2016 at 20:46
  • No, do not plug the lines, repair them.
    – Moab
    Aug 8, 2016 at 20:57

3 Answers 3

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tl dr: Could you? Probably. Should you? No.

Engines with a return line need to have it intact or you will be creating over pressure on the entire fuel system. This would cause you to dump more fuel into the engine, plus cause the fuel system components to be overworked, which could lead to other failures. If any part of the system is weak, it would most likely show it. Since it isn't designed to run as a closed system, you could most likely have been causing your vehicle far greater issues. I'm sure the High Pressure Fuel Pump in these cars is not cheap, as most I've seen are not (other makes/models).

By finding something to replace the hose, you did the right thing. Even though it was a hassle, it is far better for your car than the alternative.

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  • So it sounds like it's possible, but only to be done in dire circumstances with the likelihood of damage increasing with distance travelled.
    – Travelling Man
    Aug 8, 2016 at 21:26
  • @TravellingMan - I think it really depends on the vehicle make, but yes, absolutely. Just realize, the more you run it, the more potential for damage. And not any cheap damage. You did right.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Aug 8, 2016 at 21:41
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You don't say the specific engine in your car but assuming it's one of the 1.9 TDI's, I'd say it's definitely a bad idea to run with the fuel return "to air" or blocked.

I have a 2003 Bora (Jetta IV) 1.9 TDI PD130 which has a "fuel cooler" fitted in the fuel return line under the front floor pan. Doing some research on this, I discovered the reason it's there is that the fuel returned from the engine is so hot that it would melt straight through the plastic fuel tank if returned uncooled. Add this to the fact that fuel is moving around the system at massive amounts of pressure and running with a severed / blocked fuel return line is a recipe for disaster.

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I would think not. The fuel, among other things, serves as a coolant.

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