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MG TD TF 1500 - Low Oil Pressure Cut Off

Would anyone have a schematic to wire a "Low Oil Pressure Cut Off switch to cut ignition if oil pressure falls below 20 PSI? I have the pressure switch in place and have an ignition override switch which will allow car to start and run until pressure builds to more than 20 psi. I can not find the schematic to connect. Car is Neg ground and running a Petronix.

Thanks, Sherwood
S Parker

MGB's have such a circuit. You can probably piece one together from a Moss catalog. I don't think the cutoff pressure is that high. Bud
Bud Krueger

Keep in mind when you design it that it will have to bypass that circuit whilst starting! :)
Kevin McLemore

Here is a crude design. Cut your pressure switch in on the white wire that runs from the key switch to the coil.

Since you want it to fire while cranking...run another wire from the starter side of the starter switch to the same post on the coil as the white wire connects to. You need to keep voltage from flowing back to the starter so it will need a diode in that line.

In addition you may want to put a switch in line to kill it entirely. Otherwise the engine will fire if you pull the switch, even if the key is off.

Modern cars with on and start positions key switches using selenoids would be easier.

MG LaVerne

Sher, we had an article on this in the bulletin of the abingdonroughriders.org last year.
Terry
Terry Sanders

Sherwood...

Make sure you have a light that lights when the key is on and you lose oil pressure...it will save you time wondering what the hell just happened.

Also...where are you running your pressure switch from?

Manley Ford told me to isolate the pressure switch from the engine to lessen the probability of failure from heat and vibration. I made a bracket to mount it to the bulkhead and ran it from the supply to the head where pressure will normally be the least. Here's a photo:

Gene

Gene Gillam

What happens if you're in heavy traffic and you lose oil pressure? Seems to me there are circumstances where it would be better to get out of harm's way even at the cost of destroying the engine rather than saving the engine but getting the car (or you!) severely damaged.

I'd say at least fit an override -- if for no other reason than the circuit could go wrong -- but in an emergency situation I doubt most people would have the presence of mind to use it in time.
Rob Edwards

I don't think allowing the pressure switch to kill the engine is a particularly safe idea. Better to have a lamp or buzzer wired in. Can you imagine the switch or wiring failing while in a corner at speed?
Steve Simmons

I forgot to mention I don't have mine wired to a kill switch either - there's a BRIGHT red led that comes on over the oil gauge to let me know there's a problem. When/if that comes on you've got time to kill the engine if you're in a position to do so.

Gene
Gene Gillam

Thinking back on the MGB circuit I find myself thinking that it kills the flow of fuel rather than the ignition.
Bud
Bud Krueger

modern, high revving, high BMP engines have low oil lights that do not even illuminate until approx. 9 psi. what is the significance of 20 psi.? regards, tom
tm peterson

That's what most of the low pressure lswitches are rated for....
Gene Gillam

This thread was discussed between 14/09/2014 and 16/09/2014

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