Strange Oil Pressure

[Mehetabel]

greeting collective

I am having an "interesting" problem with the truck.

Because of one thing and another I decided to replace the engine this fall. It is [and was ] a European 6 cyl. which makes engine choices "interesting" as well. I just re did the clutch and replaced the bulkhead this spring so I wanted to keep the "new" major repair as simple/ cheap as possible. I got extremely lucky and found a direct replacement that the Australian Military had rebuilt and crated "for future needs."

I had the new engine put in [there are limits to what can be done in a gravel parking lot ] and it performed beutifully for the first day I had it back [~80 miles of city, stop and go driving]. The next day I was doing some tiding up on the vehicle and decided "hmm the oil looks a little low, I will add some" roughly .5 qt [don't get me started on "the most advanced nation in the world" still using a system of measure based on the physical atributes of a 16th century king ].

The next "day" I decided to try and drive the truck to work [~25 miles on highway, yes keeping the revs low for breakin purposes]. I did fine until the engine reached operating temperature at which point the "low oil pressure light" [the green one on the series dash] came on. I pulled over and tried to figureout what was wrong. In the dark I could not see anything so I said "low oil pressure light, must mean low oil pressure" so I added some oil and started off again. Shortly thereafter the light came back so I turned around and took the truck home.

When I checked the oil level in the light I was now VERY high so I drained off some oil to get the dipstick level back to H. I found that the electrical connection to the sensor was loose so I tightened it and retested. Again the light came on once the engine was up to temperature. As before the light comes on [/color]mid to high revs and goes out when the engine settles to idle [yes opposite of the "typical" behavior ].

I then drained off more oil to bring the "level" under the L mark and still have the same symtoms.

I would like to hear thougths and comments as to cause, effect and solution.

cheers

John

p.s. I am putting this question up "elsewhere" also to improve the quiry base.

[trainspotter]

I would check to ensure you have put exactly the right type of oil in. It doesn't seem to be losing oil.

Had this once on a Vauxhall Carlton which had synthetic oil put in it.

As soon as it got hot the oil light came on as the oil was too thin.

Changed it back and the problem vanished.

[MarkieB]

apparently a filter that's on its way causes low oil pressure in the older style engines; particularly for V8's the ones with the old-style more feeble oil pump. I'm not that familiar with your engine, although it could be similar?

[Diff]

Hi John,

The level of oil will have very little impact on the oil pressure providing the level is between the high and low marks. As you say, the fact the oil light comes on at revs and not at idle is the opposite to what you would expect. If you have access to another known good oil pressure light sender, try fitting that and see what happens(perhaps the one off your old engine?). Ideally you should borrow/buy an oil pressure guage and fit to see exactly what is going on. Check the earthing of the engine to the chassis, and the switch to the block.

If the oil light was coming on when hot at idle it would suggest either a worn engine, oil too thin, engine getting too hot(cooling system fault) or a worn pump. But these are not the symptoms you are getting.

Hope this helps,

Regards,

Diff

[Mehetabel]

Ok,

The saga continues [in slow motion due to work load and weather/ time constraints involved with exterior parking ]

I changed the oil and filter in case it was caused by "lay up" oil/ wax buildup in the filter and got the oil level back to its proper place: no change

I borrowed a gauge [Range Rover fitment]. Spent a day trying to fit it to the pressure relief valve [wrong :crazy:]. BTW no gunk found in the valve. Spent a day trying to fit the guage to the pressure switch location [the right place], spent a day trying to get the correct fitting [FYI it is 5/8 BS Course for a series engine ] including the "miracle" hardware store that has everything [once got bolts there that were metric hex head with a SAE thread], and a specialty British car repair shop. Went to visit the local "wonder mechanic" who told me that he had sawn the guts off of an old pressure switch and tapped the new end to take the metric fitting from the guage. Borrowed the fitting from him. Finally installed the guage today [a pain as the starter motor has to come out to get at the location]

Upon startup the pressure is ~15 -20#. Once the engine is warmed up the idle pressure is 10 -12#. At rev [20 -30 mph] the pressure drops to 6 -8#.

Conclusion: The pressue switch is good, I have a problem .

In light of the new information this thread is back up for more input and discussion.

Thanks for your help

[Les Henson]

Oil pressure relief valve stuck open perhaps?

Oil pump gears badly worn?

Personally I would take the engine apart. Low oil pressure means wrecked engine if you don't sort it asap.

Les.

[Diff]

Ok,

The saga continues [in slow motion due to work load and weather/ time constraints involved with exterior parking ]

I changed the oil and filter in case it was caused by "lay up" oil/ wax buildup in the filter and got the oil level back to its proper place: no change

I borrowed a gauge [Range Rover fitment]. Spent a day trying to fit it to the pressure relief valve [wrong :crazy:]. BTW no gunk found in the valve. Spent a day trying to fit the guage to the pressure switch location [the right place], spent a day trying to get the correct fitting [FYI it is 5/8 BS Course for a series engine ] including the "miracle" hardware store that has everything [once got bolts there that were metric hex head with a SAE thread], and a specialty British car repair shop. Went to visit the local "wonder mechanic" who told me that he had sawn the guts off of an old pressure switch and tapped the new end to take the metric fitting from the guage. Borrowed the fitting from him. Finally installed the guage today [a pain as the starter motor has to come out to get at the location]

Upon startup the pressure is ~15 -20#. Once the engine is warmed up the idle pressure is 10 -12#. At rev [20 -30 mph] the pressure drops to 6 -8#.

Conclusion: The pressue switch is good, I have a problem .

In light of the new information this thread is back up for more input and discussion.

Thanks for your help

Very strange symptoms as you would expect the pressure to rise with revs, as it seems ok at idle. Only things I can think of are perhaps the pressure relief valve spring it too weak or the wrong one, and as soon as the flow/pressure increases with revs, it opens thereby losing the pressure.

Another possibility is that there is muck or debris in the sump partially blocking the oil pump pick up pipe. As the revs rise, the pump cannot maintain flow due to the restriction and pressure is lost.

I agree with Les that you need to get it sorted before putting any more miles on the engine.

Regards,

Diff

[Mehetabel]

Very strange symptoms as you would expect the pressure to rise with revs, as it seems ok at idle. Only things I can think of are perhaps the pressure relief valve spring it too weak or the wrong one, and as soon as the flow/pressure increases with revs, it opens thereby losing the pressure.

Another possibility is that there is muck or debris in the sump partially blocking the oil pump pick up pipe. As the revs rise, the pump cannot maintain flow due to the restriction and pressure is lost.

I agree with Les that you need to get it sorted before putting any more miles on the engine.

Regards,

Diff

Thanks for the replies guys. I had the relief valve apart as part of the process of getting the gauge on [stupid current owner did not know whether to install it on the relief valve or the pressure switch ]. The internals of the relief looked fine/ came in/ out easily. The spring felt quite stiff [someone had previously suggested "streaching" it, which I was unable to do on a quick try].

The intake very well might be blocked as someone has managed to bend the sump [silly Diggers ]. I would hope that the pump had been rebuilt with the rest of the engine but the oposite is rapidly becoming apparent.

Does anyone know of the availability of rebuild kits and the possibility/ viability of bench testing the pump?

cheers for the advice and I will keep you posted

John

[MarkieB]

I know rimmer bros looked a good source for that kind of need, there are others too as I daresay people'll be along in a while to say..

[Mehetabel]

FIXED, running "normally" again

Dropped the pan: this took a day and a half as the stupid thing was literally glued on with paint. The final solution [dont try this at home kids ] was to put the front end on jack stands, run a pipe between the stand legs and pull the sump down with a hand winch .

Looked inside and did not see much of anything. The pump screen was clean [dripping with oil but clean ].

Fortunately I had "picked up" my "spare" sump, oil pump, and pressure switch when I moved the old engine last week [stored at a friends house across town].

Since there was nothing obviously wrong I rolled the dice as to which of the three was the "cause" of the low pressure [bent sump, stuck relief valve, duff pump] I decided to try the pump first as it was/ is the hardest to "check" for problems [the engine had previous worked with the sump dent and the guts of the valve checked out ok].

New pump in and everything back together.

Fire it up. Shut it down and the "new" pressure was finding some nice leaks where the filter attached to the block and was higher than I expected [80 -100# on the choke at startup].

Started up again. The idle pressure came down to ~40# when the choke was off and continued to drop as the engine warmed up until it settled at the "normal" 8 -12#. My oil pressure now RISES with revolutions. The guage I was using was leaking BADLY at one of the junctions so I did not test for longer than absolutely necessary .

Removed the guage today [harder than it sounds as the starter has to be pulled to get at the fixture] and tested again on the idiot light. Normal results, I can now get on with everything else on the list

Thanks to everyone for your help, suggestions, and support in this time of trial and tribulation

cheers

John

[Les Henson]

Well that's good news.

It doesn't say a lot for military re-built engines though does it?

Les.

[Mehetabel]

Well that's good news.

It doesn't say a lot for military re-built engines though does it?

Les.

No..., but they did their job well enough for the engine to get out of the "depot" and back on the road .

The engine ran fine in the shop and for the first day and a half after its installation before going t*ts up again .

To their credit I suspect/ expect that they never worked on the oil pump during the rebuild and it just chose this time [why now ] to give up the ghost.

cheers