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Question Oil Pressure Drop

My oil pressure gage used to peg at 5 bar when first cranked and at idle until it warmed up. Once warmed I would get 4.5 bar at anything above 3Krpm and 3.0 bar at warm idle. Now, when I first crank it I get 4.5 bar until it warms and then 4.0 bar at anything above 3Krpm and 2 - 2.5 bar at warm idle. I was running Amzoil 10W40 when the drop occurred so I decided to switch to Amzoil 20W50. I saw no pressure increase when I switched to 20W50. I don't have any severe lifter noise and even with this drop it still is within the specs described in the owners manual.

I know it could be either the sender (but not likely since they usually fail high), the OPRV, or the crank bolt not tight enough. I don't particularly want to just start changing parts and I don't have a way to add a mechanical pressure gage. Should I just keep an eye on it until I start hearing lifter noise or should I stop driving the car immediately and start checking the above? Any help is appreciated. The car has 139K miles and the rod bearings were replaced at 100K.

Thanks!

A.J.

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Old 02-23-2008, 03:50 PM
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Thats very odd that it happened suddenly. I have had various pressure readings on various motors. Sender and gauge problems usually fail high as you mentioned. It could be that a piece of dirt, gasket, bearing or something got lodged in a passage blocking flow? OPRV could have a problem with the spring. Is there any milkshake or rise in engine temps as compare to before?
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Old 02-23-2008, 04:14 PM
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No milk shake or rise in the engine temps as compared to before. When I drained the oil I checked the drain magnet, oil, and filter for bearing material and I didn't find any. My oil does smell a little like gas but it is not thinning and it smelled that way before the oil pressure drop. I thought about trying one of those oil analysis services where you send them a sample of oil and they send you back an analysis. I did pull the plugs to see if the injectors were leaking into the cylinders but I didn't find anything and all the plugs looked good.
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Old 02-23-2008, 04:37 PM
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Check and clean your grounds.

All the instrumentation do wacky things when corrosion builds up.
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Old 02-23-2008, 05:51 PM
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That is good point, I haven't considered the ground connections. However, the gage is not jumpy or erratic. I have seen the ground diagrams for ground location and I have the electrical schematics for the car. Which grounds are the most relevant for the instrumentation?

Thanks

A.J.
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Old 02-24-2008, 03:14 AM
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You can screw a gauge on where the sender goes. The hard part will be that you don't have a reference to what the pressure was before the drop occured but it might help you figure out what the actual pressure is.
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Old 02-24-2008, 06:39 PM
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Well...wouldn't you know it, I started getting severe lifter/tappet noise today. So I pulled the OPRV and disassembled and cleaned it. I replaced both Orings and put on a new crush washer. This made no difference to the oil pressure or tappet noise. I guess the next step is to put on the mechanical oil pressure gauge and possibly do a compression test. Any ideas?
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Old 02-25-2008, 08:05 PM
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Were the main bearings replaced? One of those could be going. Hard to tell without being there.
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Old 02-25-2008, 08:36 PM
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The main bearings were not replaced but the noise is definitely in the cam tower not the bottom end. Are you thinking bearing material clogging the tappets and keeping them from pumping up?

A.J.
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Old 02-26-2008, 03:35 AM
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The problem with the lifters is low oil pressure. Did you retorque the crank bolt?
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Old 02-26-2008, 10:02 AM
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I haven't re-torqued the crank bolt yet but that will be the next thing I do and I will report back. Assuming that I can trust the oil pressure gauge, would 4.5 bar at cold start still be to low of an oil pressure to cause lifter noise? It's hard to tell but I don't think all of the lifters are making the noise. I tried the long screwdriver to the ear to pinpoint the noise but no luck. I have to say that it is a little disheartening to let the motor run for very long with this noise.

I really appreciate the help with this from you guys.

Thanks!

A.J.
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Old 02-26-2008, 10:31 AM
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One would think that 4.5 would be enough to keep lifter noise away....but I'm not totally certain.
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Old 02-27-2008, 04:06 PM
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I checked the crank bolt torque and it is at least 160 FT-LBs. So that rules out a loose crank bolt for causing the "lower" (since 4.5 bar at cold start is acceptable according to the owners manual) oil pressure reading.

Assuming the gauge is correct and the fact that I am getting lifter noise, I think the reduced oil pressure is real. I checked the OPRV and it definitely wasn't stuck and the spring seemed firm but I don't have a reference for what firm is. Could the spring be weak causing the OPRV to open too early thus causing reduced oil pressure. If so, I think this would also explain why my oil pressure did not go up at all when I changed from 10W-40 to 20W-50. Other than buying a new OPRV ($3XX.XX, Ouch!) what is the next logical step?

I didn't get the lifter noise until shortly after I switch to 20W-50. Should I switch back to 10W-40 and see if I still get the lifter noise? Or, do I do a compression test to see if I have a stuck/collapsed lifter on one of the cylinders? Any help is appreciated.

Thanks
A.J.
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Old 02-27-2008, 07:00 PM
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Hey AJ,

I wouldn't do a compression check. The key to fixing everything is to get your oil pressure right. I was thinking there was a guy here that just changed his OPRV and that wasn't his problem...you might PM him and see if you can borrow his old one to see if that is the problem. That way you wouldn't have to buy one to see if that is the problem. I would definitley put a gauge on the sender unit to see what your actual pressure is. The guy that should have an extra one to loan you is Tidybuoy. He is a pretty nice guy, so maybe he will do that if you pay the postage. I need to look at the manual to see if there an oil passage way that you can put a gauge on before the OPRV. I think there might be but I'm not sure.
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Old 02-28-2008, 07:28 PM
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Tom,

I agree 100% about the oil pressure. I need to fix that first, then see what happens with the lifter.

Some additional information. I think I have located the lifter that is collapsed. I listened again with the long screwdriver to the ear and I could ear the loud clacking noise coming from the very rear of the cam tower, implicating cylinder #4. I pulled the plugs (which have less than 200 miles on them) and the #4 plug was fouled. It wasn't wet but it was lightly coated with backed on oil/fuel.

Thanks for the lead on the OPRV. I will send Tidybuoy a PM.

I really appreciate you sticking with me on tracking this problem down. I can do the work, I just need someone who has the experience with these cars. I have only had the car a year and I am getting very familiar with it.

Thanks again!

A.J.

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Old 02-29-2008, 06:46 AM
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