Citroen XM Forum

citroenxm wrote: I had a feeling Mechanical Pumps didn't run except with oil.. But wasn't confidant enough to be sure

You can be confident Paul as you were absolutely right in your earlier post All I did was flesh it out a bit..

Air ingress into a mechanical pump will cause the engine to run roughly and with great hesitation to rev much above idle. O a semi-mechanical like the Bosch AS3 it'll cause the timing to be upset as that's under hydraulic control with the fuel as the medium.

I've seen a CAV pump running high due to entrained air, but it wasn't high enough to be considered a runaway.

Dieselman wrote:I've seen a CAV pump running high due to entrained air, but it wasn't high enough to be considered a runaway.

How high Will?

Probably about 2,000 rpm.

When my Brother worked in a commercials garage, one of the mechanics rebuilt a fuel pump and decided to test run it with the governor detached. That engine went very high...for about 1 minute.

2000 rpm is just a (very) fast idle..

Dieselman wrote:That engine went very high...for about 1 minute.

Followed by ka-boom no doubt and the guest appearance of a conrod exiting the block stage-left...

The 1.9TD XUD I spoke of earlier that raced due to an over-full sump lasted a long time. Long enough allegedly to blow the top hose off the thermostat spigot and still it ran.

I'm not sure now what the final fate of it was. I guess it seized up in the end but as far as I know it's didn't break as such...

I must dig the story out of the FCF. It was fully documented on there about six or so years ago...

Tough old birds, the XUD engines...

Jim, when you say grossly overfilled, how overfilled? Like 5 mm above max o n the dipstick say... I have read horror stories of overfilled sumps and diesel cars going nuts. Many videos on you tube too.

russ92xmsed wrote:Jim, when you say grossly overfilled, how overfilled?

5mm over is not a problem Russ, I'm talking two or three litres over at least..

The case I was speaking of was caused by a duff oil level sensor and the owner kept on topping up and up and up trying to make it go out. It did eventually but not for the reasons he hoped

Another cause of a race can be diesel leaking into the sump and raising the oil level. If you see the level magically going up that's not the magical XM self-fixing going on but a real problem. It's virtually unknown on the XUD but used to be a problem in engines that had mechanical lift pumps - like old-school petrol pumps - driven from the engine cam and slapped on the side of the crankcase. Engines with jerk pumps could also suffer but invariably these were industrial engines and not automotive ones...

Back along, the Lister H series, used to drive - amongst other things - generating sets, used to suffer quite badly and it was essential to check the oil very regularly because of this.

Broken piston rings can cause diesel to leak into the sump but again you'd know there was a problem anyway with other symptoms and in DI engines it can be caused by dribby injectors - I believe there's several well-known examples of car engines (not PSA) that suffer badly from this and cause them to self-destruct in the end when things get bad enough...

Welcome Dave,
As you see someone will figure out what is the problem.

Regards,
Norman

CitroJim wrote:

russ92xmsed wrote:
Another cause of a race can be diesel leaking into the sump and raising the oil level. If you see the level magically going up that's not the magical XM self-fixing going on but a real problem. It's virtually unknown on the XUD but used to be a problem in engines that had mechanical lift pumps - like old-school petrol pumps - driven from the engine cam and slapped on the side of the crankcase. Engines with jerk pumps could also suffer but invariably these were industrial engines and not automotive ones...

Back along, the Lister H series, used to drive - amongst other things - generating sets, used to suffer quite badly and it was essential to check the oil very regularly because of this.

Broken piston rings can cause diesel to leak into the sump but again you'd know there was a problem anyway with other symptoms and in DI engines it can be caused by dribby injectors - I believe there's several well-known examples of car engines (not PSA) that suffer badly from this and cause them to self-destruct in the end when things get bad enough...

I've seen a lister raising the oil level tot he extent it needed an oil change every day until maintenance could be performed at eh w/e.

Modern diesels with DPF have a tendency to pollute the engine oil with diesel, if only used for short journeys.

CitroJim wrote:

russ92xmsed wrote:Jim, when you say grossly overfilled, how overfilled?

5mm over is not a problem Russ, I'm talking two or three litres over at least..

The case I was speaking of was caused by a duff oil level sensor and the owner kept on topping up and up and up trying to make it go out. It did eventually but not for the reasons he hoped

Good lord! I always go by the dipstick. I don't rely on gauges ect. When I did my change, I took two days to get the level right! I got in 5 litres and then slowly kept adding more little by little till it was fine. I know...totally unessessary, but it worked for me!

My oil level gauge didn't want to play today...