Be wary of old OEM oil pressure switches


I have an OEM oil pressure switch in the block as a coolant pressure switch. It failed. I’d never seen one of these fail before. I pretty much thought they were bullet proof.

My coolant pressure warning lights have been acting funny for a couple months and I finally got around to looking into it tonight. I figured that the problem would be the banks of LEDs that are my warning lights. To my surprise, the problem turned out to be the OP switch. I had several spares so it’s now replaced and working fine.

It would be a bummer if someone was still depending on the OEM OP switch as their sole indicator of OP. Then one day…Boom.


fails open or closed?


Kind of in the middle. With no pressure it’s supposed to be open. >7psi it’s supposed to be closed. Mine wasn’t quite closed it was at high resistance all the time. It was running some high intensity LEDs in my case but obviously the OEM solution is a small incandescent light.

I don’t know if I can draw any conclusions on a logical failure mode. My LEDs were kind of half illuminating, but potentially a small incandescent bulb wouldn’t illuminate at all. It’s all kind of fuzzy land, so I’d assume a failure mode that would be especially bad. Murphy’s a mofo.

A big incandescent warning light wouldn’t have illuminated with a loss of pressure. That’s sure. I don’t know about a small incandescent light tho.