Bizarre oil pressure - low on cold start, higher after warmup

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Aug 20, 2012
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Searching the forum I can't find any posts describing this condition.

'96 FZJ80, 1FZ-FE, 210,000 miles.

This is a recent development.
On cold start (temps around 40F) I'm registering nearly zero movement on the oil pressure gauge.
After warmup (coolant at full operating temp) oil pressure registers just below the first mark. Goes up and down with revs, but not above first mark, and not as much as was normal in the past.

In summary: Gauge shows no pressure on cold start, but shows some (low) pressure after warmup. Basically backwards from what is normal, and lower than normal.

No oil consumption
No coolant consumption
No mechanical noises
No power loss
No unusual temperatures

Recent work:
Head gasket 15k miles ago. Good compression.
Front seal and oil pump cover seal 4K miles ago (I.e., crank bolt)
Blue fan clutch and mod 4K miles ago
Oil change 1,200 miles ago with small Napa (Wix) filter (only thing available at the time)


To do:
1) check crank pulley bolt for proper torque. (I did the crank seal 4,000 miles ago)
2) measure pressure wth a mechanical gauge
3) oil overpressure bypass?
4) defective filter?

Anyone seen this condition before? I'm open to any advice.
 
Joined
Jul 28, 2015
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Lewiston,ID
I saw this exact condition about two months ago. Lasted about 4-5 days, then went away. I chalked it up to a faulty gauge. 3 weeks went by, no issues, no noises. Them I was coming back from a 300 mile round trip ski weekend. Pressure dropped again. Noises started happening. Lost the rod bearings, now the block, head, etc are at the machine shop, and I am about to order close to $3K in rebuild parts.
Still not sure what caused it.
Not saying this will be you, but I would definitely get it checked out.
 

Dave 2000

Not all Land Rovers are useless!
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The oil pressure gauge is VERY sensitive to battery voltage, when calibrating the sender the battery has to be hooked up to a charger. When first starting the engine the battery voltage will be lower than when the engine had been running for awhile. Such low overall readings indicate a problem with sender unit or hopefully not the engine anyways. A new sender should sort things out or pull and recalibrate your existing unit. Check the actual pressure with a master gauge for peace of mind before you do anything.

regards

Dave
 
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I fixed an identical problem on an old Explorer by replacing the oil filter with a premium oil filter. I would start there.
 

bloc

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I'm not basing this on experience but speculation.. possible air leak in the oil pump pickup which allows air in while the oil is cold/thick, but draws less air when the oil is warm/thin?

Agree with the advice to hook up a master gauge for verification. Stock sender is 1/8-28 BSP thread for the record.
 
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I had a bad napa gold oil filter 1515 big can one, and drove it about 10-20 miles on low oil pressure. i started getting ticking from the bottom end of the motor. I replaced the filter, and oil pressure returned to normal. The ticking has progressed, and to resolve it, the bottom end of the motor is going to require work. The consensus of the local club guys is piston slap. Top of the con rod and wrist pin and piston were starved of oil, and got a little damaged. That happened two years ago, and I know that motor will need to come out and be replaced.
 

baldilocks

Battle Ground, WA
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If you end up replacing the sender understand that they are not all identical with regards to indication.

I replaced mine because the sender itself was leaking. The replacement indicated much lower pressure. The second new replacement sender indicated a little higher but not up to te normally agreed up "normal" gauge reading.
 
Joined
Aug 20, 2012
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Tri-Cities, WA
Status report:
Crank bolt was properly torqued. I applied 320 ft lb and it didn't budge.
Found the sender ground lead (slide connector) seemed to be seated poorly. Cleaned up both terminals.

Dash gauge is reading steady on the first line now with little movement as revs change. Not sure if this is an improvement or just because the engine is still hot. Will check again in several hours when I can do a cold start.

Nobody local (I mean nobody) has a pressure test gauge in stock. Have to wait until tomorrow. Tomorrow will check with test gauge and change filter. And report back.
 
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You probably just fixed it. I would squeeze the slider contact with pliers to make a tighter fit, and spray all contacts with DeOxit.
 

Dave 2000

Not all Land Rovers are useless!
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You will find the adjustment is easy enough so you get the correct reading but, opening the sender can be a pain, if it is leaking then you will need a new one, there should not be any oil in the sender unit itself. I have found even new ones do not read correctly but there should be significant movement between idle and 2000 rpm, mine sits at the top of the gauge when at 2000.

regards

Dave
 
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This makes me really wonder about my 80. When at an idle it will drop to nearly no pressure, but comes right up with the rpms. In the owners manual for the 96 it says this is normal for the oils pressure gauge, but I have never had a vehicle that acts this way.

It is a newly rebuilt motor with a new pressure sensor and a new connector for the sender.

I do have a CEL for p0133 and P0401. The motor has about 2500mi on it since rebuild.
 
Joined
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Changed the filter and what do you know.
I hope the defective filter didn't destroy the engine. It never gave any audible or other outward signs of starvation, but it still makes me nervous.

 

bloc

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Run the oil for a few thousand miles then catch a sample for a used oil analysis. The lab will be able to tell you if anything is wearing prematurely.
 
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