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By Gary - 15 Years Ago
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Recently completely rebuilt 55 Merc 292. Engine has approx 300 miles and I noticed oil underneath rear main area and dripping out of crank breather tube after driving. Installed a cheap oil gauge that reads 0-to-80psi and engine reads 60 at idle and about 78 at rev-up. (probably max for gauge, pressure may be higher). Should I change oil pump? If I make the change how will I know the replacement won't be the same? Oil pump new and installed by machine shop during rebuild. Thanks, any help appreciated.
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By petew - 15 Years Ago
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Are those readings with the engine hot ( operating temp ) and what weight oil are you using ?
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By speedpro56 - 15 Years Ago
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What's the pressure at cruise say at a constant 2000 rpms after warmup. At revs don't always tell us much unless it's going much higher. 78 when cold and revving I don't see as a problem.
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By marvh - 15 Years Ago
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I seen an y block once with that kind of oil pressure +50 at slow idle and +80 psig at cruise.
When we took the engine apart we found the rebuilder had installed the connecting rods in the wrong order meaning #5 was in #1's place and rest the same order. The rebuilder had built it as a chebby.
My boss at that time explained that the y block V8 connecting rods have a greater chamfer on the big end's the opposite side to its partner rod to fit the curvature of machining of the journal fillet. With the lesser chamfer installed on the journal fillet side there was less clearances and then a higher oil pressure result.
anyone ??
marv
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By Speedbump - 15 Years Ago
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80psi isn't enough to damage bearings, etc. At worst, it can cost a tiny bit of engine efficency, maybe in gas mileage. With an external pump, it should be an easy task to change the tension on the pump pressure relief spring. A slightly weaker spring will give less oil pressure. Also during this process, you can ensure the relief piston is sliding freely in it's bore. A stuck relief valve can cause this problem. Almost all connecting rods have a chamfer for the stated reason, but if installing them wrong didn't result in metal contact with the fillet, I doubt it would have any effect on the pressure. It is the clearance between the journal and the bearing, usually .001" to .002" that helps determine the working oil pressure. In order for rod side clearance to affect pressure, the clearance would have to be tighter than the bearing clearance. I've never seen it get even close. I would not suspect improper assembly to be a cause for the higher than normal oil pressure.
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By MoonShadow - 15 Years Ago
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How about the oil pressure relief in the filter? Chuck
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By Ol'ford nut - 15 Years Ago
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I don't think your oil leaks have anything to do with your oil pressure. As far as the oil pressure I would just drive it and watch. As for the leaks, what rear seal did you use? Wouldn't be the first new seal I have heard of that leaks. You have to be very careful installing them. Only thing you can do now is do it over to fix leak.
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By Gary - 15 Years Ago
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The oil filter has been converted to spin on type and oil is 10W30 w/zddp additive. I installed the oil gauge yesterday and today was the first road trip with engine at operation temperature and speed. At 55-60 mph oil preassure was 70 psi, stop and put in nutral, and had 42 psi, dropped in drive (lowered idle speed) and had 22 psi. My main concers with high oil pressure is pushing oil out the gaskets, main bearing seal, crankcase breather, etc., which is occuring with the main bearing seal being pretty bad. Thanks all for your suggestions & input.
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By charliemccraney - 15 Years Ago
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22psi at idle is fine. Oil pressure is not going to push oil out the rear main, or breather; you have other problems. The only gasket pressureized oil travels by is the head gasket. Do you see signs of oil seeping toward the middle, intake side of each head gasket?
Start with the breather and work your way back. You may find that all of the oil you see is coming from the breather, being blown to the back and looking worse than it really is.
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By HT32BSX115 - 15 Years Ago
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charliemccraney (10/5/2010)
22psi at idle is fine. Oil pressure is not going to push oil out the rear main, or breather; you have other problems. The only gasket pressureized oil travels by is the head gasket. Do you see signs of oil seeping toward the middle, intake side of each head gasket?
Start with the breather and work your way back. You may find that all of the oil you see is coming from the breather, being blown to the back and looking worse than it really is.
I agree with Charlie,
I had a stock 57 Ford (with a 292) in the 70's as a teenager (that Grandma bought new) that would "peg" my 80psi direct reading oil press gage when cold.
When warmed up, it would show 20-30psi or so at idle and 50 or so on the freeway running straight 30.
Cheers,
Rick
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By MoonShadow - 15 Years Ago
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Actually that range sounds really good. I sure wouldn't worry about the startup pressure. Chuck
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