oil pressure light coming on

hoggyrubber

last 2 times I have started and drove my 53 hornet the oil pressure light blinked some after it had warmed up after and hour or so when the engine kicked down to an idle. I read the thread about placing a washer under the spring on the oil relief valve and did this after the first time it did this but it did the same thing the second time I drove it. after reading more I can only think of 3 causes.
1. when I cleaned out the oil pam a couple of years back I think the o ring was in bad shape that connects oil pickup. I think I replaced it with a regular o ring. I read on a thead it needs to be a specific one.
2. then I replaced the gear on the oil pump I redrilled the hole and used the larger pin that was sent. I had to get a little aggressive stacking the pin ends, but pump turned freely when I was done.
3. oil sending unit is acting up.
any suggestions on what I should do. should I hook up a manual gage in addition to the orig one. if so, is there a place to plum it in to that I won't have to mess with the orig location of the factory on under the manifold?

[Deleted User]

I think you are on the right track as far as adding a gauge for awhile to troubleshoot. Then you will know the true story .I think you could add a "T" fitting to where the sending unit is fairly easily leaving old sender to continue operating.

[Deleted User]

Did you replace the oil switch? Change that before you go to other things. Switches go bad. Walt.

Frankvintagefullflowcom

Addition of washers under the spring will make no difference in pressures below the "crack point" of the regulator since the regulator exhaust port is covered by the plunger during conditions where the pump output is less than the volume necessary to maintain maximum designed pressure. The pressure regulator is out of the circuit below that point. It will increase pressure on the upper end of the range, but that's not where you need it.
Walt's right in that the switch can leak internally (you don't necessarily see it on the outside) and cause a false indication. Typically that will be a situation at start-up where the light goes out, then comes back on as the oil pressure equalizes on both sides of the diaphragm. The time that takes depends on the size of the leak. It sees that as a "no pressure" condition.
Also check for a short to ground in the wire to the switch. Since the switch is a device that grounds the indicator light circuit, a frayed wire or one rubbing on the exhaust pipe will make the light go on, usually intermittently or a flickering effect.
F

J Spencer

As stated the first thing to do is insatall a 'master' oil pressure gauge in place or 'tee'd in with sending unit to verify correct oil pressure. Probably a bad sending unit. I have replaced many of them for that problem over the 40 years I was a mechanic.

My own 51 Pacemaker did the same thing, I was about two miles from home on the x-way doing 65mph when I noticed the oil light on. No knocking from the engine so I got the car home, put the master gauge in, oil pressure was perfect, got a new sending unit the next day at Advance Auto Parts where I was working, put it in and all is fine. I did have to change the wire end connection but that is all. They all work off the same principle, when the oil pressure is low the sending unit gounds the bulb so it lights. Pressure opens the circuit. The main difference in switches is the amount of pressure calibrated to open/close light circuit.

ernie28

On my Pacemaker I have gauge permanently installed sitting nicely under the dash in a double black VDO unit along with an ammeter. I prefer to be able to see exactly what is going on rather than just rely on the lights. For the oil, I just put a tee where the sender attaches and it works well for my peace of mind.

hoggyrubber

thanks Roger, Walt and everyone. I am going to add the manual oil gage back with the tee as mentioned. I had the gage in till I redid all the electrical stuff and just went back to all orig stuff.
hate to ask a bonehead question but is the switch you guys mention the same as the sending unit? or is it under the dash? I have totally rewired the car, but kept all the orig electric stuff except wires. thanks, stacy k

PAULARGETYPE

IT'S THE SWITCH ON THE RIGHT SIDE OF THE ENGINE THAT MOUNTS ON THE END OF A SHORT PIPE UNDER THE EXHAUST MANAFOLD

hoggyrubber

very good, that's what I was thinking. can I still get them at parts store or online somewhere?

PAULARGETYPE

PARTS STORE I DON'T HAVE THE # HERE IN THE HOUSE

Lee ODell

Driving home on the freeway one night the oil pressure red light came on. I shut the engine off and costed to a stop on the shoulder of the road. We, my wife and I, sat there for awhile thinking about how we were going get ome 50 miles away. I had recently bought the Hudson and was getting used to it. Then I remembered there was a mechanical oil pressure gauge under the dash. Got out the flash light then started the engine, what a relief when the gauge was reading 50 psi. We drove home with red light on and plenty of oil pressure. My wife kept the flash light on the gauge all the way home.

In a previous post I asked questions after installing a rebuilt Twin H 308 about low pressure problem, 20 psi and less. Walt gave the solution. To remove the timing cover to see if there was a bolt missing behind the timing gear. The bolt was missing and after installing a new bolt the oil pressure went right to 40 psi.

Lee O'Dell
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hoggyrubber

thank you both. Mr O'Dell, I remember that thread. while I had the mechanical gage hooked up it ran good oil pressure all the time, so I hope it's not that bolt missing. I don't think the timing cover has been off this engine in a looooong time if ever. I plan on hooking the mechanical one back up and I will replace the switch at some point.

Ol racer

FYI

Same thing happened Gauge Press good with Sender only Yr old....Had wrong Sender with incorrect Pressure setting... You need #PS15 Standard or equilivent....

[Deleted User]

My swaps book also names other part #'s for a sending unit .
Echlin: OP6415
Stewart / Warner: D-364L
Standard: PS149

Lee ODell

I added that last part of my statement in case someone with a new motor had low oil pressure. I suspect as others you have a sender problem. You would have heard terrble noises if that bolt came loose and contacted the timing gear.