92 accord dx, manual, 250k miles, 5W-30. I recently replaced the head and a bunch of other stuff. Then I tore it apart again and replaced the piston rings.

After driving on the highway for several minutes my oil pressure light comes on when the engine is at idle. (If I hold the clutch in or come to a stop.) It isn't full brightness... sometimes it's barely flickering on, sometimes it's dimly lit. If I rev the engine even slightly (1000 rpm) the light goes off. The light never comes on while I'm driving. If I shut the car off for 10 minutes or so then restart the light is no longer on at idle. Once I get it heated up again the symptoms return.

This has started since I replaced my piston rings. I accidentally overfilled the oil by a half quart... so I drained some out but not enough. The oil is currently about 1/4 quart above the top mark. I don't know if this could cause an oil pressure problem.

I noticed the light come on before I replaced the rings, but never at idle. If I released the clutch poorly and the engine speed dropped below 500 rpm the light would flash bright for a split second, and sometimes it would switch to constant flashing until I restarted the car.

Anybody have a hunch? Should I have replaced/serviced the oil pump while I was replacing the head? Does anybody know what pressure the sensor switch trips at? Sure would be nice if oil pressure gauges were standard...

 

I would say the best course of action would be an oil pressure test, you'll need the adaptor for the oil pressure tester that screws in where the oil pressure switch is.
the thread size is 1/8 BSPT.
The minimum oil pressure to keep the switch open is 4.5 PSI.
When you had the head off did you replace the 'O'ring on the oil jet orifice that sends oil from the block to the head?
Replace rod bearings, or main bearings?

 

I removed the jet orifice but I don't think I replaced the O-ring. The gasket kit I bought came with about 30 O-rings in a bag, none of them labeled. Most of them I was able to figure out by inspection... fuel injectors, spark plug "tube", etc. The old o-ring wasn't cracked or anything and I figured I'd be better off leaving the old one rather than replacing it with one that looked similar but might be wrong. (I made that mistake with the thermostat housing O-ring.)

I didn't replace the bearings because that seemed like something that could be done from under the car at a later date. Could that contribute to oil pressure issues or were you just curious?

It seems unlikely but could the pressure switch be bad? I have a spare in my junk accord in the garage... seems like an easy swap and test.

 

Correction... I had 10w-30 in the engine, not 5w-30. It was a 5 quart jug of Mobil '5000' 10w-30 from walmart... the cheapest stuff I could find.

I changed the filter and oil tonight... used Kendall 10w-40 this time. Somewhat miraculously the oil pressure light did not come on once in over 20 miles of driving. I'm baffled.

How could the switch from 10w-30 to 10w-40 increase my oil pressure enough to keep the oil pressure light from coming on. It seems like I must be operating very close to the threshold of that pressure switch.

 

take the DUDE advice and chk the oil pressure, that way you will know if it is a mechanical or electrical issue .....you do not want to let it go and find out in a few thousand miles that you have to rebuild the lower end ..

 

That sounds like some advice I shouldn't pass up... a friend of mine has an oil pressure gauge he's going to lend to me so I can hopefully figure out what's going on. Any advice or links to information on how to properly do an oil pressure test? Do I just monitor the pressure to verify that the switch is operating properly or is it more involved than that? I searched the forums but didn't find much detail. Any help is greatly appreciated! (My Haynes manual is a piece of $^%*.)

 

You can download a shop manual for a 91 accord that has all the info.

When the car gets to operating temperature the oil pressure should be a min of 10 psi. At 3000 rpms, the pressure should be a min of 50 psi.

If the pressure is within range, then replace the pressure switch. If the pressure is too low, then you will have to inspect the oil pump.

 

thicker oil raised the pressure? hmmmmm, sounds like mains to me.

 

From the luck I've had with this car I wouldn't be at all surprised if it turns out to be the mains. It's quite apparent the engine was neglected... amazing the rest of the car is in decent condition. I just might have to take the block out of my junker and start rebuilding it now, so when this engine finally bites it I have something to swap in.