low oil pressure at idle--sometimes - Defender Source
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Old February 4th, 2006, 01:52 AM
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Corey K-nig
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low oil pressure at idle--sometimes

I've got a Defender 3.9 that all the sudden, at idle, started to show low oil pressure on the gauge and the light will flicker or stay on until idle is increased. Has about 130,000 on it, but it's been taken care of rather well. My question is, is it typical for the oil pump to go out? It appears to be on the front of the engine and a bear to change out. I've pulled the pan and it looked clean. There was some gunk in the pan but the pick-up was clear. Would like to hear some "I changed out my oil pump" stories. Thanks!
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  #2  
Old February 4th, 2006, 08:56 AM
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Mine does that sometimes when the oil is getting old, reminds me to change it. What viscosity are you using? You say you have a gauge as well? or just the light?

The oil pump actually isn't too bad to work on, though I've rarely seen oil pumps of any type fail. Maybe just needs a new pressure spring, they can get gunked up over time and start to stick. The pump body is actually the timing cover, so it does take a while to change it totally, but you can also try rebuilding it in place with a new set of gears and possibly a shim to reduce any clearance gaps.

The only thing to remember is that you need to re-prime it if you take it apart, and that means pack the thing solid with petroleum jelly for the initial start-up.

-Hans
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Old February 4th, 2006, 04:16 PM
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Corey K-nig
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I was hoping it was a sign that the oil need to be changed. I had 10-30 in it and went to 10-40 but I still had the issue. I have both a gauge and a light. When the gauge gets real low, the oil light comes on or flickers. Can you tell me where the pressure spring is located? Is it something I can buy seperate or does it come with the pump? Have you heard of the sending unit for the light and the sending unit for the gauge going out about the same time? That may be my next step. Thanks for the input!
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Old February 4th, 2006, 11:39 PM
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If both the gauge and light are dropping in pressure, it's probably not a sender or gauge related at all. (unless they feed from the same sender). At that kind of mileage, it is also possibly but very unlikely that it could be internal wear in the engine...... that kind of stuff requires a full rebuild to replace all the bearings, but you can usually go with a thicker oil (15w30 or 15w40) to help it get along for a couple more years. But normally you don't see that kind of stuff until much later, unless things have been really neglected. And you might as well check all the easier stuff first anyways.

I'd highly suggest going through the whole re-priming process if you take anything apart on the pump other than just the sandwich plate or filter..... otherwise you risk blowing the whole engine. The pressure spring is in just the right spot to drain the pump if you take it out. Give yourself a couple hours to do this, as you're basically taking the whole pump apart. No matter what, you should get a new gasket too.

It will also give you a good chance to inspect the whole thing and clean it out. The whole unit is serviceable and rebuildable and It takes less time than dropping the pan probably, as long as you have the right sized 12point box wrench for the bolts. All the bolts have 12 point heads on them for some reason. (Just don't lay under the oil pump directly, and have the gear fall down onto your face and split your lip open..... ask me know I know about this.). Just make sure to take your time, and be very clean about it. And don't damage the gasket surface cleaning the old one off by using a screwdriver, it's one of the important ones that you want to seal as good as possible.

When you get the bottom cover off, two big gears will drop out, these are what pushes the oil through. Don't let them hit the ground, it could chip them. One has a shaft sticking out, the other a hole in the middle.... you can't mix them up putting them back in. They can sometimes wear when they spin against each other, and also check the face of that bottom cover itself where the gears rub... this is the biggest cause of pressure loss over time next to a worn spring. If that plate is worn down in an oval shape and is anything other than perfectly smooth, you should replace it and the gears.... and that costs about $200 for the cover, The gears are about $50-60 for the pair. The pressure spring and plunger shouldn't be more than $15-20, gasket $5 or so. Just make sure to check for actual wear, as that area will be discolored for a few reasons..... this is nothing to worry about, but if you can see/feel any actual worn metal then you need a new one.

The pressure spring and plunger are under a bolt/plug on the side of the bottom cover, make sure to flush out and clean that whole thing pretty well. If you have another car, maybe even take it to a local parts store that has a machine shop and ask them to run it through their cleaner. (if you do this, take the senders out so they don't get damaged).

It all bolts together the same way it comes out. But there are two things to remember.
1. You need to pack the whole gear housing full of petroleum jelly (vaseline), this gives it extra suction that it needs to prime the oil system if the pump has been drained. I packed mine about 1/3 full before I put the gears in, packed the gaps between the gear teeth, and packed it again once I put the gears in. It won't hurt anything, and is how it's done at the factory (Same exact process on old AMC V-8's as well).
2. You will need to spin the gears around so that the tab on the shafted gear engages the slot in the bottom of the distributor. Don't worry, you can't get it backwards, nor can you get the gear all the way in without doing this.
3. When you put the bottom cover on, don't use any kind of silicone sealer in a tube, just use the gasket and hi-tack (Brush on gasket glue).

When you start the engine again, it may make some tapping noises as the lifters re-pressurize, but it may not since yours already have oil in them. But keep an eye on the pressure gauge and make sure the pressure comes up again. Mine took about 10-15 seconds when I did the new camshaft to fill the new lifters and the rocker assemblies.

-Hans
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Old February 6th, 2006, 09:55 PM
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Corey K-nig
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Hans

Thanks for the intense info. I pulled out both sending units and made sure they weren't gunked up. I then pulled the spring out and made sure that it was clear. While I was under there I checked out the star shaped bolts. That is much better to deal with than pulling the entire front cover off. The book I have doesn't go into as much detail as your post so now I'm ready to dig in a little deeper if need be. If my oil pressure continues to stay low, rebuilding the pump will be next. I won't be dreading it as much now, though. Your response is much appreciated. Man--Thanks!
Corey
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Old February 7th, 2006, 01:10 AM
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Not a problem. Just make sure to watch the pressure again at startup to make sure the pump hasn't lost its prime.

-Hans
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