low oil presure

[chazzwic]

went out today 350gm motor oil pressure fine when you stat up when it gets hot it drops started to lose power oil guage under 20 at idle shut it off sat awile then brought it right in please help

 

[mla2ofus]

Re: low oil presure

Just had a thread about this same problem recently. Someone suggested checking to see if motor oil is overfull w/ the boat sitting in the water. If it is the crankshaft will foam the oil causing an oil pressure loss. If this isn't the problem then I'd say the cam brgs are getting too loose.
Mike

 

[wca_tim]

Re: low oil presure

first thing to do is check the conections to the sender and hook up a mechanical gauge to verify that what you're seeing on the gauge is representative of what our engine is really doing. Stinks to chase an oil pressure problem when the gauge is where the problem is.

Oil pressure loss from foam is typically something that would happen at high rpm... when things are really churning in the crankcase. it can trash an engine in a hurry under those conditions. at lower rpms ranges, overfull crankcase usually makes oil pressure higher and if you get on it, blows seals out.

Was this gradual or did it drop sort of all at once. if the latter, is probably nmore likely a gauge or electrical problem... at least in my experience

 

[dr_bowtie]

Re: low oil presure

20psi at idle hot is fine...

a small block chevy will run all day long at 4psi idle no issue...

loose clearances will cause a drop in pressure when the oil gets hot but if it is consistent everytime there isnt much to worry about....

now if the hot oil pressure was high at idle and then dropped or it was low and then gets higher there is something to worry about...

 

[chazzwic]

Re: low oil presure

sorry it took me so long to come back me and a buddy put new main bearings in this engine but we didnt do the rod bearings idle when it gets hot is low 15 to20 psi when you get on it it goes up to 40 psi is there a chance its the rod bearings an also i only used 10w40 oil would it make a big difrents an i did start to lose power after 3grand rpm runing it didnt want to go coulrd these all be the same problem

 

[Bondo]

Re: low oil presure

idle when it gets hot is low 15 to20 psi when you get on it it goes up to 40 psi

Ayuh,.... What are you expecting to see,..?? 10psi per 1000rpms is within Spec...

Are these #s verified with a mechanical gauge, or just the dashgauge,..??

 

[Bifflefan]

Re: low oil presure

a small block chevy will run all day long at 4psi idle no issue...

never going to buy an engine from you.

 

[gadget73]

Re: low oil presure

To the OP, 10w40 is thin for this application. 15w40 or SAE30 is typical for a marine engine. If you're losing power, I doubt the oil pressure is the root of your problem. What you're showing indicates an engine with some hours on it, but it doesn't tell me anything is doomed in the bottom end. It might have low compression or other problems, but I don't think you're going to find its bearing related.

Also, simply replacing bearings without checking the dimensions of the crankshaft almost never fixes low oil pressure, especially if you can't determine for sure that the low oil pressure was caused by the crank bearings. If the main bearings were worn, I can pretty well promise you the crank is not quite in spec either. Usually you need to have the crank cut and use an undersize bearing, or at a minimum the crank ought to be polished and checked with a micrometer to see what kind of shape you're in. It could also be worn cam bearings, or worn rod bearings, or even a clogged oil sump or a worn out oil pump causing the problem. Diagnosis is the most important part of any repair.