Repeated Oil Pressure Switch Failures

[imoutnumbered]

I have done a couple searches for oil pressure switch problems, but haven't found anything quite like my problem.

I have gone through two brand new oil pressure switches over the course of very few hours. I have a 2002 Regal with a 2001 5.0L Mercruiser, 2 barrel carb. I don't have the serial # handy at the moment. The first failure late last season was after running 10 minutes and being shut off for about 1.5 hrs, wouldn't start or stay running if it did start. Problem was isolated after bypassing the switch allowed it to run flawlessly.

Second time was the first trip this season. Boat started right up after winterization at the shop and at the marina. Ran it to operating temp before heading out (after already having been towed in once because of this). Engine ran great for probably 2-2.5 continuous hours, different speeds, then out of the blue acted like it ran out of gas or someone turned the key off. After checking for water in the filter, I jumped the oil pressure switch wires and the boat fired right up and ran like a top back to the marina.

Two entirely different conditions, both with new switches. Boat has less than 75 hrs on it, engine and terminal connections are immaculate. Oil pressure readings show midrange on the four hash mark gauge, no other known issues with the power plant. When checked, there are two nice full streams of fuel going into the carb, as the fuel pump runs fine. Gas is good/fresh, no smoke out of the exhaust, circuits appear normal when checking the afflicted circuit.

While there are a number of things that could cause the symptoms, there has to be something with the switches being that a jumper alleviates the problem and allows the engine to run without incident.

I appreciate your theories and suggestions...​

 

[imoutnumbered]

Re: Repeated Oil Pressure Switch Failures

It is the brass T for the oil pressure sender and the switch. Once it gives out, I am only able to start and run it with a jumper in place.

I will be going to the boat this afternoon to have a look at a couple other things as well, and if I have the right stuff with me I will pull the T assembly and run wire through it to see what I find.

It's odd though, because once it fails, it doesn't want to start up even after a "cooling off period". I don't know if the time I left it sit was enough to drain a blockage out or not.​

 

[Bt Doctur]

Re: Repeated Oil Pressure Switch Failures

defective switch?

 

[muc]

Re: Repeated Oil Pressure Switch Failures

"circuits appear normal when checking the afflicted circuit."
have you tested how many amps are running through the oil pressure switch?
Good Luck Muc

 

[JustJason]

Re: Repeated Oil Pressure Switch Failures

that's what i'd be checking to. How much current is going throught the switch. It shouldn't be alot, maybe a couple of amps. You may also have a voltage drop going on in that circuit. You may want to check how many amps your fuel pump is pulling also.

 

[imoutnumbered]

Re: Repeated Oil Pressure Switch Failures

Haven't checked for amps or voltage drops in the circuit. With my switched jumper line I have in there, I could check the fuel pump draw, but if I remember my electrics right, won't I have to run the engine to check at the oil pressure switch?

I don't have my wrenches this weekend either, so checking the T pipe will wait until next weekend. Hopefully there will be decent weather so I can get it back in the water.

Thanks for the tips, will check and report back.​

 

[Don S]

Re: Repeated Oil Pressure Switch Failures

With the jumper wire on, the pump should run with just the ignition switch in the run position, remember oil pressure is what makes the switch make contact. your jumper is now the oil pressure.

 

[imoutnumbered]

Re: Repeated Oil Pressure Switch Failures

Checked the juice to the fuel pump, it reads about 900mA and about 11.2V across the terminals (with the engine off).​

I checked pictures of our boat sitting in the water and adjusted the trailer to the right attitude. I hate to admit this, but I found that the oil was overfilled by perhaps a quart, which was immediately drained. How likely is this to affect my problems--or rather, to what severity does too much oil affect pressure? The oil appeared fairly fresh with no evidence of foaming. With the oil fill cap removed, the valve area looked clean as well.​

When we tested the last failed switch on compressed air (about 10psi), we saw an intermittent zero/infinite reading on the ohmmeter at a steady pressure (using alligator terminal clips). Since we weren't using precision tools, there is a good possibility of human error in the mix.​