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Old 09-21-2000, 07:08 PM
jc300e's Avatar
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Join Date: May 2000
Location: Location: Norcross, GA
Posts: 124
92 400e....124, M119...
oil psi gauge jumps two 1 or 2 when ignition is turned on...upon start, gauge jumps immediately to 3...
do i have a bad psi sensor?
if so, where is it on th v8 and can it be changed by a diy'er
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Old 09-21-2000, 07:51 PM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
Yes you have a bad sending unit! It's mounted to oil filter housing on the right side of engine. Not difficult.
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Old 09-22-2000, 10:04 AM
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I just replaced my oil pressure sending unit on my 92 400e. Very EASY DIY job.

Make sure that the sending unit is the problem before you start.

From what you discribe, it may be the gauge inside the instrument cluster, but it is fairly common for the sending unit to go out on these cars.

Crawl under and remove the sending units signaling wire, there is only one wire so it is pretty easy to identify.

With the car off, the pressure gauge should read 0. Turn the car ON, but don't start it. Pressure gauge should now read 3, this is due to the open circuit.

With the car still ON, ground the pressure gauge's signal wire to the frame or other ground. The gauge should now read 0.

If you do replace the sending unit, make sure you have a container to catch the oil that will come out of the mounting location.

Good luck!

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Old 09-22-2000, 06:04 PM
jc300e's Avatar
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Location: Location: Norcross, GA
Posts: 124
thx for the advice...just in time for some weekend DIY'ing...

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Old 09-22-2000, 07:26 PM
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I though the pressure gauge should always be on '3'. My car('89 300E) is always at '3'. Is some wrong? What is the right level during normal driving condition? Thanks.
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Old 09-22-2000, 08:59 PM
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No, the pressure gauge should not ALWAYS read 3. I should read 3 when you are driving or putting any type of load on the engine, driving, reving, etc...

Once the engine is warmed up, the gauge should normally be around .3 to 2 when idle.

If you turn on the car, but DON'T start it, the gauge should read 0 since there is NO OIL PRESSURE. Upon startup, it should read some pressure. If you are reading 3 even when the engine is not running, then you have a problem. Either the gauge or sending unit is bad. Chances are it is the sending unit.
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Old 09-22-2000, 09:16 PM
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Does it do any harm if the pressure gauge does not work properly and sending unit is bad? Thanks for your reply.
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Old 09-23-2000, 12:57 AM
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Well as long as your engine is working properly and getting oil pressure, then I would say no, it wont hurt anything.

Remember, the oil pressure gauge is an informational device. Not all cars have one. You still have a low oil light to tell you if you are running low on oil, so the oil pressure gauge gives you more info to help monitor the engine.

My oil pressure gauge on my 400e read 3 ALL the time before I replaced the sending unit. I drove it like that for months, I just felt that a car as fine as my 400e deserved to have everything functioning correctly.

Hope this helps!

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Old 09-27-2000, 01:54 AM
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Join Date: Mar 2000
Location: Fairfax, VA
Posts: 1,249
This is interesting.

My 89 260E spikes to 3 on startup and stays there until the engine warms up. Then it drops to 2.

I assumed this was normal but this discussion suggests otherwise. So, how should it behave?
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Old 09-28-2000, 09:31 PM
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Join Date: Jul 2000
Location: British Columbia, Canada
Posts: 827
The oil pressure gauge should indicate a substantial amount of pressure after a cold start. Think about it. When oil is cold, it's still relatively thick requiring more effort to pump it through all of the lubrication journals and therefore registering increased pressure.

As the oil heats up, it thins out (basic thermodynamics) and is therefore easier to "move" through the engine. Thus, less effort and in turn pressure is required.

I deally you'll want the gauge to be at 3 all of the time. However, if it shows 1.5-2 at idle while warm, that is perfectly acceptable.


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