Hudson low oil pressure

I run a Hudson engine race car in a vintage class.  The engine is a 308, bored .060, and has 7X modifications.  Last year the oil pressure got to be a problem as you could start a race with the gauge reading 50 psi and after about 6 laps it would be down to 0 psi.  I am  using Valvoline Racing oil VR1 20-50.  The engine does not run hot.  The engine was torn down recently and the clearances all checked out OK.  I did change the oil pump.  It was suggested I try an oil accumulator which I did and added a  Morosco 3 qt. over the winter.  Racing last week the oil pressure did the same thing--starting the race with 50 psi and having it drop to 0 in about 6 laps.  I would welcome any suggestions to fix this.  Thanks.


  • Assuming your oil pressure switch is electrical, it could be as simple as a bad oil pressure switch or wiring.  As the car heats up from the driving, the heated electrical components don't work as well.  There is a fair amount of heat released by the exhaust near where the oil pressure switch is located.

    Good luck.
  • rcfalk
    rcfalk Member
    Thanks for interest, but I am taking the oil pressure from the other side of the block from the plug where the oil is diverted to the filter when there is one.  I have a "T" with two mechanical oil pressure gauges connected and since they both give the same reading I am assuming they are both working.
  • Geoff
    Geoff Senior Contributor
    You are taking the pressure reading from the wrong place.  You need a T-joint at the pressure switch  fitting, to an oil gauge.  
  • Is there something in that oil filter circuit that shuts down flow during certain conditions to preserve full flow to the rest of the engine?
  • atc
    atc Member

    From the 1952 Mechanical Procedure Manual

    Oil pressure is regulated by a built-in nonadjustable release valve and spring accessible through a plug at the left rear side of the engine. When starting the engine the release valve has moved to a position that closes the oil passageway to the oil filter and allows full pump flow direct through the main oil gallery extending the full length of the crankcase.

    I wonder if this valve is still in your motor and in operating condition. If so, it may be working as intended.

    I have always taken a pressure reading from the other side of the engine block down by the fuel pump on the oil pressure switch. I bet under stressful load or sloshing due to an unbaffled oil pan, when flow drops, the valve will shut and you won't get a reading. I would be interested in seeing readings taken from both locations and see how they compare.

  • Geoff
    Geoff Senior Contributor
    Yes, it is a by-pass system, not full flow.   Therefore if the oil gets hot and pressure drops, less oil will go to the filter.  
  • Ol racer
    Ol racer Senior Contributor
    edited May 2022
    Install a good mechanical gauge at the original location where original sender goes,.. Is the small bolt hole behind timing chain gears plugged with a bolt when 'drip trough' to lube chain was removed from front of block?  With Zero pressure motor would seize and/or knock

  • rcfalk
    rcfalk Member
    Thanks for all of you for your comments and for taking the time to respond.  We do not race for a couple of weeks so I will change out the location of where I am taking the oil pressure and put it back on the other side.  I am thinking it might be interesting just to leave one gauge connected on the left side just to see what the difference is.  The comment about the release valve was interesting to me.  I better check that out also.  Thanks--I really appreciate your help.