I bought a 1998 Disco I last week with 160,xxx miles. I have been driving it around near home for a week with no problems. Today I took it to work (I am a master Audi tech), and after 20 miles the oil light began to come on. I read some forums, and most of them point to a possible loose oil pump pickup. I took the pan off after work (really easy, and heavy) to inspect it. It all looks ok, however I took it off anyway and cleaned it out. The pickup screen was a little clogged, so I cleaned it out in the parts washer. I didn't remove any bearing caps, but I couldn't see any material squeezing out from the caps. I also put a magnet in the pan and I couldn't find any metal.

Here is the situation, the oil pressure light stays on for 10-15 seconds sometimes on start-up. The light is off until the engine gets really hot (20 miles), and then the light only turns on when I press the gas. It doesn't matter how hard either. It only takes a light application and the light turns right on. It turns off immediately when I take my foot off the gas. I also changed the pcv hoses, the little plastic guy (seperator) in the pass side V/C was clogged solid. I had to drill it out. There is also a weird howling noise that comes from the passenger side that starts at 70 and goes away at 80. The light turns off when the noise goes away, but it may be coincidence due to the engine speed. Also, the knock sensor is broken on the pass side head, is this related?

Now, I need to actually check the pressure with a gauge, but nothing sounds loud and it runs pretty good. I would think that the engine would be really noisy if the pressure was that low. It could be a sending unit, but wouldn't that be all the time? Is there some sort of "computer logic" that monitors oil pressure and throttle position? The way I see it, at 2500 RPM, the engine turning the oil pump and it is pumping x amount of oil. Wouldn't the light be on "off" throttle also? What does load have to do with it? Is there something else going on? Can I rebuild the oil pump, or does it need to be replaced?

 

what oil did you use when you change it and does it smell like gas... i got somewhat the same problem again so good luck

 

Nope, the oil was actually clean. I also changed the oil and filter (Fram with no drainback valve, does this matter on these?", I used 10w30 Penzoil.

 

The oil filter is why your oil light stays on so long when you start the truck, your oil pump is loosing its oil and needs to prime everytime.
You need to dump that oil filter, I use NAPA Gold or Purolator.

Also anything that is xW-30 is to thin for these engines in the summer, winter time your fine (unless you live in the south).

There is zero computer logic to the oil pressure, the switch is right above the oil filter, $20 at AutoZone.
The switch is a simple on/off switch, oil PSI above 8 and no light.

These things can be very very picky about motor oil and oil filter.
Try a NAPA (WIX with NAPA label) filter and 15w-40 motor oil and see what happens, if nothing else you are only out a oil change.

 

Do the NAPA filters have a anti-drain back valve? 15w-40, sounds extreme!! That still doesn't explain why the light only turns on under load.

 

I've actually never seen an oil filter without an anti-drain back valve. If you look at the base of the filter, where it screws on, and look at the little holes that you will see a rubber skirt underneath them. This is the anti drain back valve.

http://www.calsci.com/motorcycleinfo...backValves.jpg

Also, the land rover filter angles down, so it would be hard to lose a LOT of oil out of it, even if it had no valve. (I'm still a big fan of using a good oil filter, I won't use a fram. But a lot of the popularly recommended filters, such as Mobil 1, are made by champion labs, and look a lot like the cheaper filters also made by them)

Engine Front Cover | Land Rover Engine Parts at RoverParts.com

You say the light comes on at a load? Is the engine at high RPMs when this is happening? Maybe you have a relief valve sticking in the oil pump. Or perhaps there is sludge or trash in your oil pan that is getting picked up.

 

Extreme, LOL!!!

http://www.carbibles.com/images/saerates.jpg

Thats what I use, these are flat tappet push rod engines and they need the right lubricant or you WILL have problems.
All oil filters have the anti drain valve but some have a less effective one, Fram is one of the worst out there.

As for the oil light coming on at higher RPM, if the engine has sat all night and then you start it and rev it to 2500 RPM does the oil light come on?
I am going to guess not.
But after the engine has been running for 20-30 min or been cruising on the highway for for 10-15 min and the oil light comes on but then shuts back off after returning to idle it is because the oil return passages are clogged with oil sludge.
When that happens the oil cannot return to the sump fast enough to supply the engine with oil and the oil pump runs dry.
Remember how I said that using the wrong oil in these engines is will cause problems? This is what happens, you must use either a heavy duty oil (like diesel oil) or a full synthetic oil (alot more money)
Here is what you need to do, you need to clean out the sludge, since you're a Audi tech I am going to assume you have access to a machine to do a engine flush, once done drop the oil pan and clean up the sump and oil pickup.
And then use diesel oil and a quality oil filter, if you dont you will have this problem again.

 

Ok, I checked it tonight with a mechanical gauge. And sadly enough, the oil pressure light is accurate, meaning the wiring and switch are all ok. I had next to nothing for 10 seconds on cold start-up, and that climbed to 20 psi max. When it is revved up, the pressure actually drops!! I didn't let it run too long because the gauge fitting was leaking a little and I don't want to make too big of a mess in the driveway. I am sure that I would have seen lower numbers when warm/hot. So, I have a filter (I forgot it at work). It is a "Mann" filter (Actually an Audi filter, which is made by Mann) that fits older Audis. It has a steel spring inside for the drain back valve. So this is a much higher quality filter. Are we still thinking filter, possible clogged oil passages, worn pump gears, worn bearings? I don't think it is bearings, because the engine sounds and runs fine (for now). I think it may be worn pump gears or clogged passages. The pump cannot deliver the volume for some reason when the RPMs are raised. Is the relief valve possibly clogged and leaking? Can the spring be replaced seperately?

 

I've never seen any parts other than gears for the oil pump on the 4.0L The older style oil pumps have complete rebuild kits available.
If you determine that something is wrong with your oil pump, other than the gears, you could probably find a used one that is in better shape, and then put new gears in it. I'm just not sure I could stomach paying over $500 for a new one. Especially since I only paid $1200 for my D1 when I bought it. (and that's how much I sold it for too).

 

Land Range Rover Discovery Defender Oil Pump Gear Repair Kit