MF-205 Industrial Oil Pressure Drops When Warm/Hot

[Soundguy]

oil flows over the main and rod bearings to lube them.. as the bearings wear, clearances open.. pressure drops.

oil puimps wear also.. clearances open.. pressure drops.

IMHO.. running 'S' rated oil in your 'C' rated engine did it NO favors.

15w40 'C' rated oil is spec'd for diesels. 'S' rated oil is for gassers.

soundguy

 

[jfharper]

Thanks for the replies. I'll check all that out. I'm leaning towards a complete overhall, bearings, seals, rings, liners, valve train, etc...I'm just trying to price everything out ahead of time so I can figure the cost approx before I begin. That way at the end of the summer, I can have it ready for the fall and winter, instead of still torn down wondering when I am going to get the rest of the funds to complete.

 

[jfharper]

I've been thinking about something that I can't quite wrap my mind around. If the oil viscosity is thinner (flows quicker) when cold and thicker (flows slower) when hot, why wouldn't the pressure be lower when cold than when it is hot, in the case of worn out bearings? I would think because of the clearances being more open because of wear the pressure would be lower when the oil was thinnner?

Unless the heat issue does something to further expand the clearances, and that is the main driving force behind behind the pressure drop when hot.

 

[Gale Hawkins]

cold 10 weight is much thicker than hot 50 weight.

This is not a place where applying logic makes sense.

 

[jfharper]

Ah...now I get it...thanks.

 

[Soundguy]

and in the end.. I wouldn't run an 'S' rated oil in a machine needing 'C' rated oil.

soundguy

 

[jfharper]

Absolutely. I wouldn't do all that work and not run the right oil after you mentioned it above...thanks for the note.

 

[WilliamTO-35]

If you're having to add that much oil to the engine, and there's apparently a lot of wear on the engine, it doesn't matter too much which oil you use, as long as the viscosity is high enough to maintain some oil pressure. Be certain you've double checked the oil pressure, as a single gauge or sending unit may be inaccurate. After your rebuild, however, use an appropriate diesel rated engine oil. My 1989 Chevy truck had oil pressure that dropped down to around zero at idle with 10W-30 oil. I switched to 20w-50 oil, and the pressure stays above 30 psi under all conditions. Not optimum for cold winter starts, but with 220,000 miles on the engine, I just want to keep it running for the short local trips I take.

 

[jfharper]

Will do. Any idea on how to test oil pressure gauge or sending unit to make sure they are accurate?

 

[Soundguy]

is it a mechanical gauge with capilary line or a electrical gauge with a sender?

Pretty much the method to test either is to use a known good 'spare' mechanical gauge and hook to the cappilary line or in place of the sender temporarily so you can compair readings.

soundguy