1FZ-FE Low Oil Pressure

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Fzj80 1997

Fzj80 1997

SILVER Star
10 Year
Joined
Jan 7, 2012
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115
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459
My 97 LX450 has low oil pressure... she runs and drives like a dream with no weird noises or rough idle. I removed the original sender the other day and in between installing the new one, I put a mechanical gauge on it. The numbers were 4-5 psi at idle and 36 psi at 3k.

After I installed the new sensor, the gauge is definitely reading higher when cold, but after a while it’ll go back to just a bit above nothing. Weird thing is when I’m driving on the highway at about 2.5k rpm and then let off the gas, the needle for the oil pressure will actually move up. Then when I accelerate the pressure will go back down. Anybody have any experience with this issue or know what’s going on with my truck?
 
91180 said:
My 97 LX450 has low oil pressure... she runs and drives like a dream with no weird noises or rough idle. I removed the original sender the other day and in between installing the new one, I put a mechanical gauge on it. The numbers were 4-5 psi at idle and 36 psi at 3k.

After I installed the new sensor, the gauge is definitely reading higher when cold, but after a while it’ll go back to just a bit above nothing. Weird thing is when I’m driving on the highway at about 2.5k rpm and then let off the gas, the needle for the oil pressure will actually move up. Then when I accelerate the pressure will go back down. Anybody have any experience with this issue or know what’s going on with my truck?
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There is a known issue with the gauge itself. Some internal part of the gauge become loosen and causes this issue.
 
I put in an oem oil filter today and no change. The gauge is still acting up. When I let off the gas on the highway oil pressure will go up. I recently had the crankshaft oring and oil pump seal changed. The oil pressure was pretty much doing the same thing before that. So I don’t think it’s the torque on crank.

One thing I noticed while changing the oil filter today was a leaking hose that routes under the oil pan. Anybody know what that is? I appreciate all the replies
 
If you recently had the oil pump seal done, was the gauge acting this way PRIOR to that fix?

If not better check the HB torque. 304 LB-FT.
 
BILT4ME said:
If you recently had the oil pump seal done, was the gauge acting this way PRIOR to that fix?

If not better check the HB torque. 304 LB-FT.
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^^^^^

Agreed.

This is the first thing I would do. It is important that the Harmonic Balancer Bolt be torqued properly and many shops are not aware of (or will take the time to look up) the relatively high torque figure. Even if done correctly...this would be among the first things you'd want to eliminate as the possible cause.

The oil pump drive gear (95-97) is not keyed to the crankshaft, so pressure from crank pulley against the gear is what holds it in place and prevents it from spinning. Definitely something to check.
 
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My 94 with 231K+ idles at 12-13psi at fully hot in drive and 17-18psi in park and is around 65psi+ at 3,000 using 10W/30 synthetic. I don't bother with the OEM gauge as they tend to read all over the place.
 
GSTMike said:
My 94 with 231K+ idles at 12-13psi at fully hot in drive and 17-18psi in park and is around 65psi+ at 3,000 using 10W/30 synthetic. I don't bother with the OEM gauge as they tend to read all over the place.
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That agrees exactly with my '97 with 315K on it. Monitored with a digital Auber Gauge.
 
The gauge was reading low before I changed out the seals so I don’t think that’s the issue. There’s definitely a problem here. I’m thinking maybe the next thing I should check is the pressure relief valve for the oil pump.
 
Fzj80 1997 said:
The gauge was reading low before I changed out the seals so I don’t think that’s the issue. There’s definitely a problem here. I’m thinking maybe the next thing I should check is the pressure relief valve for the oil pump.
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Did you ever resolve this issue? My 1995 has this exact response, once the engine is warm the oil pressure gauge decreases when accelerating and rises when I let off the pedal. When cruising at 65 it drops as low as just above the lowest mark, but also sporadically rises back up to the middle mark.
 
CVBackroads said:
Did you ever resolve this issue? My 1995 has this exact response, once the engine is warm the oil pressure gauge decreases when accelerating and rises when I let off the pedal. When cruising at 65 it drops as low as just above the lowest mark, but also sporadically rises back up to the middle mark.
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Have you independently checked the sending unit pressure?
 
CVBackroads said:
I have not. Is this an electrical test or do I need an oil pressure gauge to check this? Thanks!
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Unscrew the sending unit and (temporarily) replace it with a live gauge. I wouldn't buy one; try to get someone to lend you one. You only need a 0-100 psi gauge.

It doens't have to be an oil pressure gauge; any pressure gauge will work, as long as it screws into the block.
 
Malleus said:
Unscrew the sending unit and (temporarily) replace it with a live gauge. I wouldn't buy one; try to get someone to lend you one. You only need a 0-100 psi gauge.

It doens't have to be an oil pressure gauge; any pressure gauge will work, as long as it screws into the block.
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Okay, thanks. This will definitely be useful information, but I would like to be able to check the pressure while driving since that's when the oil pressure gauge fluctuates. I suppose I can rev the engine while parked to see if this results in a similar response. I haven't tried that yet. I will look into this and report back.
 
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