w124 250td 1989 diesel leak

[nickdub]

Hi,
just bought this car and having had a quick look at it today, the most obvious problem is a diesel leak in the engine compartment. It's not got an obvious source but seems to be coming from somewhere near/under the fuel pump.

Is it possible to run the engine with the air-filter off in order to get a better look at what's going on ?

The car is starting and running OK. Apart form the obvious loss of fuel, is there likely to be a problem in running it this way for a few weeks before getting the leak sorted ? I'd like to try to establish if anything else needs doing, which will probably only become clear if I can actually use the car.

Finally any recommendations for garages/mechanics in the Ross-on-Wye or Gloucester areas gratefully received.

Cheers Nick

 

[wireman]

You can run it without the filter BUT remember that its like a huge vacuum cleaner that will pick up any loose items it can, if this happens the leak will be the least of your problems.

The only two major problems regarding running with the fault that I can think of are

1 COST, at a penny a smell it could bankrupt you

2 Safety, Diesel fuel makes very slippery road surfaces, do not tell any motor cyclist of the predicament or he will get his mates to burn or otherwise immobilise your car, Constable Law and the MOT man will also take a dim view.

My first guess at the fault would be the injector return pipes, they are the black flexible pipes from each injector back to the pump/tank. The tube is easily obtained from most car shops and if the car is of any great age should be replaced anyway, about a fiver.

On the back injector (No5) the second return union is plugged, make sure that the plug is good.

The delivery valves have seals on the flat deck of the delivery pump which may be at fault, I would get a diesel bloke to do this since you are entering territory where special tools and experience help greatly, and big bills could follow if you get it just slightly wrong.

The fuel pipes to and from the tank come up on the lefthand side of the engine and have shortish flexible pipes connecting the fuel pre-filter (at £2 a pop, so put a new one on) to the pre-heater on the side of the block (lowish down) and to the lift pump (on the side of the delivery pump). A additional pipe runs from the delivery pump return to the tank. These pipes are all prone to ageing and would be my second guess. Fit new hose clips if any of this pipework is dismantled.

Verify that the fuel main filter has a good seal on its periphery and its central mounting bolt (2 "o" rings) atop the filter bracket.

Cleaning with a pressure washer will help you identify where the leak is from, rinse the leftover oil film off with white spirit if needed. At this stage the application of crack detector developer (aerosol talc) will show up any leaks even tiny ones you would not normaly find. A hand full of normal talc will work if you can get an even film onto the job. Re apply protective engine wax once the jobs sorted or all the nice clean engine bits will go rusty.

There is a possibility that the leak is on one of the high pressure pipes from delivery pump to injectors, if this is the case do not get your fingers near the leak while the engine is running, it can (though rarely does) result in diesel being injected into your blood stream through the skin, you do not want this to happen, tighten the pipe nuts if the leak is here but don't do so unless you need to.

Any leak which is not from a pipe or such is best left to a profesional with all the necescary equipment for the overhaul and adjustment of the pump unit.

Good luck, enjoy the car and please let us know what you find wrong with it.

 

[nickdub]

Hi Mr Wire,
Thanks very much for the detailed reply.

I'm going to try running the car for at least some short trips as I'd like to pick up any other problems before I phone a garage. Being a bit on the mean side, I'd prefer to do some of the simpler maintainence jobs myself; however as I don't have a garage available to work in, anything requiring much time will have to be postponed until the weather warms up a bit.

I'll update the thread once I've made some more progress - the leak, though it looks messy, may not amount to more than 2 cc of fuel over a 2 hour drive - so I don't think I'm going to create any unofficial skid pans !

 

[nickdub]

Hi,
Had another quick look today as the outside temperature was quite mild

I think the second guess of the pre-filter maybe correct as there is most fuel in this area ie under the air-filter housing. I noticed that the filter is a staright through clear one which I thought was fitted to the earlier W123 models not the one with a pipe at right-angles to the main body. Anyone have an opinion as to whether another straight through filter should be fitted ie does the type matter? The current one has jubilee clips holding it on so I guess they can be re-used OK ?

Thanks

Nick

 

[dieselman]

The pre-filter should be under vacuum, the main filter under pressure. I'd go for the leak-off pipe leaking.

Just dry the area and have a look for wetness or tie a piece of paper towel round it, you will soon see staining.

 

[nickdub]

Hi,
Thanks for the advice.
Doesn't look like a problem with the leak-off pipes although it is difficult to see around the last one nearest the bulk head.
I've bought some 1/8th pipe on the off chance. Will try this first as it looks like the simplest part of the system to reach and will report back as and when I manage to achieve something.

Cheers

Nick