Oil pressure drops when engine warms up - Defender Source
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  #1  
Old September 1st, 2011, 07:03 PM
flananuts
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Oil pressure drops when engine warms up

I have a 94 D90 and the engine oil light flickers and goes solid when the engine idles. When the engine is warm the pressure goes down near 7 psi. The light goes off when the rom's increase a bit. I had the oil pan dropped mandate there was a little sludge and unfortunately some metal min the pan. There's no loss in compression though. Any thoughts on what could be the cause of low pressure? Could I have clogged oil ports from metal shavings?

Thx
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  #2  
Old September 1st, 2011, 08:39 PM
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Charles Galpin
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Did you check the screen on the oil pickup to make sure it's not clogged? If that's fine then the only thing I can think of is the oil pump. Others will probably say this is "normal" for these engines. What oil are you using? Perhaps try a thicker oil?

I am sure you have checked, but the oil level is good right?
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  #3  
Old September 1st, 2011, 10:59 PM
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David Short
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I had this on a 3.5 liter. I replaced my oil pump and bought me an extra year from the truck (maybe 5K miles). Then it came back.

In the end it was a rebuild for me. Crank bearings were likely the culprit from the autopsy - they showed signs of heavy wear and discoloration. Note that the top bearing shows more wear than the bottom bearing - if you pull a sample bearing off and just look at the bottom bearing then you are not getting the whole picture (do not ask how I know).

With the pan pulled - you can replace the piston crank bearings fairly easily. You will not be able to get to the front or rear main crank bearings, easily. This might be a cheap try-it-and-see manauver. An engine rebuild purist is probably choking at this advice. They would want the crank pulled and measured and polished and reinstalled with plastigague and all of the other "right" rebuild methods. However I wager you could replace just your piston bearings and see some benefit.

The other place you could be losing pressue is in the rocker shafts.
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  #4  
Old September 2nd, 2011, 02:30 AM
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Clay DeWan
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How many miles on the truck? I would go with Charles suggestion and remember if you change the pump and the gears, pack the gears full of wheel bearing grease as this will help create the vacuum needed to suck up the oil from the pan. My 94 had about 280K before I killed it by not properly filing it with coolant and my oil pressure was really low at idle especially when the engine was hot.
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  #5  
Old September 2nd, 2011, 06:47 AM
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Charles is dead on with this one. We see it here all the time.
Drop the pan and clean the pickup,..Reseal the pan with Right Stuff.
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  #6  
Old September 2nd, 2011, 08:52 AM
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William Skidmore
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Dont know what difference there is between grease and petroleum jelly, but in the book says to pack with the petroleum(?) jelly.
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  #7  
Old September 2nd, 2011, 09:26 AM
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I know this is going to sound odd, but on mine it ended up being a leaky fuel injector. Gasoline was dripping out the injectors after shutdown, and working its way into the oil. Eventually it would lose its viscosity and the pressure would start dropping (at about the 3000 mile point.)

Is it coming out very thin, and very black, when you do an oil change? If so, consider getting your injectors rebuilt.

-Hans
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  #8  
Old September 2nd, 2011, 10:15 AM
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I put 15w40 in and it still showed the issue. Pan was dropped and cleaned so no pickup issue there. The engine has 78k miles ad I bet the original oil pump. I'm planning to replace the oil, water, and serp belt as well as a mech oil pressure and temp as well. I'm prolly going to ride this motor till she kicks since I'm looking to do a TDI replacement in the future.
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  #9  
Old September 2nd, 2011, 10:33 AM
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Don Bunnell
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Matthew - did you drop the pan yourself? How was the oil pickup? I took some pics when I did my cross seals: http://www.defendersource.com/forum/...8&postcount=31 I spent at least an hour cleaning the pan and oil pickup up. Let me know if you want to get another set of eyes/ears on it.
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  #10  
Old September 2nd, 2011, 10:48 AM
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Hey Don. I may take you up on that. I had foreign cars do it but I think I'm done paying and will get backup doing myself.
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  #11  
Old September 2nd, 2011, 03:44 PM
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Don Bunnell
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Yeah, stuff like dropping the pan and cleaning will be cheaper and most likely better than having Foreign Cars do it. At $100 an hour it will get expensive fast and I am sure the mechanics there won't be too down with scrubbing parts for any length of time. Holler when you want to meet up.
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  #12  
Old September 2nd, 2011, 05:19 PM
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Chris Davis
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It could be the above suggestions, but the distributor driven oil pump sucks and was only marginally good to begin with. I have a RRC and a 94D90 and they both have issues with oil pressure. Even on a brand new rebuild of the engine, the stock pump sucked. That is why I am done fighting my pump and going to a crank driven front cover.

I have to run thick oil in my RRC and even then I still have issues.

If it is a new issue, take a look at the above, but it is also possible that the oil pressure bypass valve is stock on yours--it is behind the big brass threaded plug/nut on the oil pump. If you open it, you have a good chance of loosing your prime which means opening the pump and repacking with vasoline which is why I always have some extra oil pump gaskets.

Really, I hate those fn pumps.
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Old September 2nd, 2011, 07:40 PM
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Another suggestion that could help. Consider removing the sandwich plate and oil cooler lines, and run without the cooler in the loop. It may help boost the pressure a bit.

I also suggest ditching the idiot light and fitting a proper oil pressure gauge in there. Idle pressure is one thing, but pressure at higher RPM's is much more important.

-Hans
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  #14  
Old September 2nd, 2011, 09:12 PM
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I've always heard the rovers were low pressure high volume. I've never heard complaints on the distributor driven oil pumps.
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  #15  
Old September 4th, 2011, 10:25 AM
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I'm definitely down with putting a proper oil temp/oil pressure gauge in. Does anyone know if theres one that uses the curent sensor but rigs up to a gauge?
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Old September 4th, 2011, 10:51 AM
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There might be something in the FAQ's or Tech section for that?
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  #17  
Old September 6th, 2011, 02:04 PM
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Dave Johnson
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The stock "sensor" is just an on/off switch, so it won't work with anything other than a light. You can remove that and use an after market gauge in its place. The thread is pretty standard so just about any gauge would work or you can always get an adapter that fits the port on the pump, if needed.
Fuel dillution will kill your pressure. Be sure you have solved your leak or you will be chasing your tail.
I have always used vaseline per the manual.
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  #18  
Old September 6th, 2011, 06:17 PM
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Thanks Dave

I don't seem to have a fuel issue as another poster stated. I read that the oil filter can also be a culprit, so I'm swapping the Fram(crap) for a Wix and I'm going to get a true sensor. A strange and puzzling thing happened as well. I had a solid 30 minute drive at about 75mph to get home over the weekend, all highway miles, and that damn light stayed off, makes me wonder if I have more of a temp issue. Anyway, thanks everyone for the help.
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  #19  
Old September 7th, 2011, 11:54 AM
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Thumbs up Oil Pressure Gage

http://www.defendersource.com/forum/...8&postcount=39
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  #20  
Old September 7th, 2011, 12:12 PM
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Nice write up Grover, thanks!
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