oil pressure erratic- any ideas?
 

What would cause the engine oil pressure to drop 20 lbs ( 70 to 50) at mid range rpm at random? The engine oil temp was the same. I noticed this after an oil and filter change, Napa Gold 1742, tried another filter (same type) and had the same results. The engine is a 572 cu in, supercharged, intercooled, with thermostatic oil cooler. The gages were checked (swaped with the other engine), it is the engine. Any ideas? Thanks John B

You said you switched the gauges, are they mechanical? If not, what about the senders? I would recommend hooking up a mechanical gauge to make sure where the problem lies.

Maybe try to isolate the engines from the wiring. Try splicing in a temporary 6' lead at the oil pressure senders and switch the port and stb OP wires. You could also and switch the port and stb OP wires at the gauges. This is an easy place to start.

Hey BIG Daddy hook up a mechanical gauge and lay it on the back seat and watch it to confirm ..good luck

sending unit ....

ditto

Yup :grinser010:

I swapped both senders then swapped both gages and the problem stayed with the engine. This is a weird one. I called Sterling and Mike was unable to come up with anything. The other motor has the same filter with out any pressure issues.
The pressure stays at 70 +- until the motor was run for 15 minutes. Then after a run to 4000 it drops to 50+-. After sitting for a while it goes back to 70. It seems like a valve in the cooler or some bypass is switching?
Thanks for the ideas

I had a problem exactly like this a few years ago. Mine was caused by the ignition wires. I had a leaky wire running by the wire to the sender and it was driving it and me nuts. It could also be the connection between the sender and the gauge. Make sure that your ignition wires aren't touching the sender wire and see if that resolves it.

Rene

I have had oil pump releif valves stick after oil changes for no apparent reason...but I would suggest getting a mechanical gauge and hook it up temparaly to take out the whole electric system and go from there..Rob

Try the wire swap only. If nothing changes, you then know it is external of the OP system...probably...

I just had the same problem and it was a combination of the 10 pin plug and the wire going to the sender. Changed the wire and cleaned the harness plug and its all good.

I did all the same stuff you did,changed the gauge and the sender twice.Varified with a mechanical gauge and started messing with things untill i found the problem. Hope this helps.

Dumb Question, But did you try and change oil filters, I had one go bad a few months ago, thought i was losing an engine, Pressure all over the place and temps up, changed the filter and was all fixed.. $11.00 !!!!

I did try a second filter with the same results. It was the same type Napa 1742 gold, probably made by Wix. Does anybody have a cross reference for this, I'd like to try a different manufacturer.

The high voltage wires is interesting, I will try this.

Rob, How did you fix the stuck relief valve?

Ben, I put a jumper wire from the port harness to the starboard sender, and vice versis, and the problem went to the other gage. Then I swapped the two senders (wires still reversed, and the problem stayed with the opposite gage. What would you guys recommend on the wiring?

These are all good thoughts, thanks, John B

Hot runnin, the boat is a 36 Skater with 572's and Quad rotors. I can't lay on the back seat, it has bolsters.:D
PS:How can you average 17 posts a day?

Had a stock 454 Mag with some erratic oil pressures that turned out to be a broken oil pick up ...

Fram 3766 AC Delco PF1054 .... Sounds like the oil is getting hot ......pressure will drop ....when you stop and let it cool the pressure will come back .... That filter has no bypass valve ...The bypass on the 502's are mounted in the block where the oil filter pad is ...not sure what block your running ....an oil thermostat not opening could casue the simptoms .....m

John,
This would indicate to me that the there is an issue with the wire (or connection) from the OP sender to the gauge. Maybe a short, cut, loose connection, etc. You have to find it or just run a new wire. I would suggest a new dedicated wire from the sender to the gauge to make sure...then decide the long term fix.

didnt he say he swapped wires (blue) and the problem was moved to the other gauge?

that tells me the prob is either the sender or the motor ....then he swapped senders (blue still rolled) and the prob stayed with the other gauge .... so......either the motor or motor ground issue ...if it was ground issue he would have water temp indication issues and other ground related issues .....Sounds like hot oil ...

John ... does the temp slowly go up and then slowly down or is it like instantious ?

The pressure goes down slowly, like a minute duration. This all happened last fall, before I put it away for the season. I have oil temperature gages, but I didn't notice a significant difference.

The block is Merlin, I believe, but could be Dart. How can I check this?

As I recall, everything is normal until is warms up and is run hard, like 3/4 throttle. Then the pressure stays low, whether rpms are 1500 or 6000. So it will be difficult to test in the driveway.

I will have to see where the oil temperature is read. It may be where it comes out of the cooler. If the oil cooler temperature bypass fails, the temperature at this point would look stable even though the pan oil temperature was going up to maybe where the oil pressure would drop 20 lbs. How many degrees, starting at 180 would it take to drop oil pressure 20 lbs. Probably good I'm running Mobile 1.

Does anyone think this is possible? Ever hear of an oil temp bypass do this?

Thanks, John B

JB

switch temp gauges to make sure your reading accurate on those also.

I lost an engine over this exact thing:(

still need a mech gauge to be sure...but if the releif valve is sticking you have to pull the pump....at that point I'd replace it