400i Oil Pressure Gauge not "zeroing" | FerrariChat
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400i Oil Pressure Gauge not "zeroing"

Discussion in '365 GT4 2+2/400/412' started by VOLTURBO, Aug 15, 2024.

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  1. VOLTURBO

    VOLTURBO Karting

    Nov 21, 2003
    71
    Halifax
    Full Name:
    Jeff
    #1 VOLTURBO, Aug 15, 2024
    Hello all.

    I'm a long-time member/lurker who has just recently purchased my first Ferrari, a 1981 400i, chassis #33563. I've been slowly repairing and upgrading over the past several months while maintaining the car in a driveable condition. I have a quick question for the more experienced (than I) 400i owners.

    A few weeks ago I replaced the oil pressure sender with a unit from Eurospares. It has the M16x1.5 thread and has 0-12 bar stamped on it. My first impressions after the install was that it reads slightly lower that the previous, original unit. I also note that it does not start at 0 with the ignition on / engine off. The needle is 1-2 points lower.

    My question is; do the the needles on your gauges move to 0 when you switch on your ignition?

    Any further info will be appreciated...

    Best,
    Jeff
     
  2. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
    1,679
    Romulus, NY (Finger Lakes)
    Full Name:
    Ken Battle
    #2 SouthJersey400i, Aug 15, 2024
    Jeff,
    When your ignition is on and motor not running your voltage at the gauges (not at battery) is likely 12V or less. When running it will be closer to 14V and give a higher reading. Does this explain your situation? Is your 400i a Seies 1 or 2? The 2's have lots of voltage loss in the wiring, maybe less in the Series 1.
    Ken
     
  3. VOLTURBO

    VOLTURBO Karting

    Nov 21, 2003
    71
    Halifax
    Full Name:
    Jeff
    #3 VOLTURBO, Aug 15, 2024
    Hi Ken,

    Series 1 car. As I haven't driven the car much and I'm still learning it's "character" lol, I'm not confident with any of these gauges to be honest. Just as I was getting comfortable with what I thought was good oil pressure (6- 6.5 kg/cm3 at 3000-3500 rpm), the gauge started acting erratic. I then ordered the new sender (which is physically different from the original). I now only see 5.5 - 6 on the gauge at speed which doesn't really bother me, but going down to 1.5 at hot idle in the city is a concern lol. I just can't remember if the original sender/gauge actually started at 0 when the ignition was on before starting the engine. I was hoping that the new sender is simply starting at a lower point which would explain the difference. I wonder if the gauge has a calibration screw on the back side? Anyway, I do plan to connect a mechanical gauge in the near future to confirm actual pressure. I might be over-thinking this, but I figure the oil pressure gauge is the most important item on the car lol...

    All I know, is that at 68,000 miles, the engine doesn't smoke and runs extremely smooth...
    Thanks!
     
  4. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    37,090
    Cowboy Capitol of the World
    Full Name:
    Brian Crall
    #4 Rifledriver, Aug 15, 2024
    6+ kgm at 3000 is pretty high if the oil is hot. 1.5 at idle is perfect, again, if its hot oil. That engine has no need for 90 + lbs of oil pressure at any RPM. We did have issues with sticking oil pressure relief valves on 400's.

    The oil gauges and senders are not very reliable. The only way to really know what it is is to test with a good mechanical gauge.
     
    Schumi and bjwhite like this.
  5. VOLTURBO

    VOLTURBO Karting

    Nov 21, 2003
    71
    Halifax
    Full Name:
    Jeff
    #5 VOLTURBO, Aug 15, 2024
    Thank you for the comments. I will definitely check with a mechanical gauge.
     
  6. Zanny1

    Zanny1 Formula 3
    Silver Subscribed

    Dec 19, 2003
    1,133
    Arizona
    Full Name:
    Mike
    #6 Zanny1, Aug 17, 2024
    I have owned two C/4's, both with inaccurate readings on the oil pressure gauges.
    My current car's gauge doesn't return to zero with the ignition on, and runs above the 6 Kg/cm2 mark when hot at 3000 RPM. At idle, hot, it dips just below that mark.
    Sometimes it goes back to zero with the ignition on, sometimes not. In my last car, the problem was a poor ground on the back side of the gauge. I still have another gauge I put in the car as a test, only to get similar results.
    I am too lazy to take the entire cluster out again, having done that a couple of times 20 years ago on my first C/4. It's all relative, and as long as I have good HOT oil pressure near the mid point, I am not going to worry about it.
    You can change the sender and get the same results. Suggest if you really want to identify this problem, you pull the cluster (first the center units, from the back, then the outer speedo and tach, from the front IIRC). Then check the ground wire.
    I would also be sure you have a good connection at the sender.
    Here's a thread from the GTC/4 forum I wrote 20 years ago.
    https://forum.365gtc4.com/forum/main-forum/5233-electrical-grounds
     
    Ak Jim likes this.
  7. VOLTURBO

    VOLTURBO Karting

    Nov 21, 2003
    71
    Halifax
    Full Name:
    Jeff
    #7 VOLTURBO, Sep 16, 2024
    Thank you for the insight! I haven't driven it much in the past month but I do have an OTC mechanical pressure kit at the ready. I will let everyone know my results in the next couple weeks...
    Jeff
     
    Schumi likes this.

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