540 losing oil pressure at 4000 RPM
09-30-2011, 07:55 AM
#21
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Yes, the .028 - .030 is a typo------.0028 - .0030. I like to run them a little looser on H bearings than I would in a car with P bearings.
I agree with the loss of pressure being constant at all RPM's if there was a clearance issue. It is not an oil temp issue either.
The pan is a Dooley offshore pan, I don't recal right off hand if it is 10 or 12 qt. It has a built in windage tray, and the oil level is about 1 inch below the tray at the full mark. I will change the pump, and re check the bearing clearance.
I agree with the loss of pressure being constant at all RPM's if there was a clearance issue. It is not an oil temp issue either.
The pan is a Dooley offshore pan, I don't recal right off hand if it is 10 or 12 qt. It has a built in windage tray, and the oil level is about 1 inch below the tray at the full mark. I will change the pump, and re check the bearing clearance.
09-30-2011, 09:52 AM
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IF... you used these heads before with no drainback issues (same volume pump) and used this pan/windage before with no pressure problems they are eliminated. Clearances although they would leak more oil this oil will drain back into the sump quickly so should not starve the pump due to drainage (and would probably show up as a pressure problem at all rpm's as I mentioned before). It really ACTS like the pump is starving but with everything being the same as from the prior engine it leaves the pump which was through some trama! 
So IF ... everything else is as you said, I got 10 bucks on the pump. You can pull apart the old pump and see if there is something obvious which would make you feel better about puting back in boat to test!
So IF ... everything else is as you said, I got 10 bucks on the pump. You can pull apart the old pump and see if there is something obvious which would make you feel better about puting back in boat to test!
Last edited by supercat; 09-30-2011 at 10:16 AM.
10-11-2011, 06:47 PM
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The boat is two hours away from the shop, but I am bringing it home this weekend. To add to the previous info, Same heads, same windage tray. It is a new block, but there was no obvious casting flash that would prevent drain back. I do have oil coolers, the stock 500hp units, and I cleaned them upon re-assembly of the engine. I am sure hoping that I find something obvious in the pump.
I do not claim to be an expert, but I have built many drag and high perf street engines and have never seen this sort of problem. It is very strange that I lose pressure only above 4000, and get it back when the RPM comes back down.
One more thing I noticed last time I had it out, the engine with the low oil pressure also seemed to require more throttle to maintain RPM at higher speeds than the other engine. In fact the oil pressure engine will only run about 5000 at WOT, while the "good" engine will turn about 5500 with no problem. The throttles are pretty well sync'd at lower RPM. Not sure if it has anything to do with it, but .......
Thanks for all the input.
I do not claim to be an expert, but I have built many drag and high perf street engines and have never seen this sort of problem. It is very strange that I lose pressure only above 4000, and get it back when the RPM comes back down.
One more thing I noticed last time I had it out, the engine with the low oil pressure also seemed to require more throttle to maintain RPM at higher speeds than the other engine. In fact the oil pressure engine will only run about 5000 at WOT, while the "good" engine will turn about 5500 with no problem. The throttles are pretty well sync'd at lower RPM. Not sure if it has anything to do with it, but .......
Thanks for all the input.
10-11-2011, 09:58 PM
#27
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500rpm difference ? Wholly crap! Pull it !
When checking the oil pump, don't forget to check the pick up tube for cracks and the pickup for a screen that won't flow the oil required.
Check out the rest of the engine too....as 500rpm difference is huge ! Did you do a compression check ? Does this engine have a lot of blowby ?
When checking the oil pump, don't forget to check the pick up tube for cracks and the pickup for a screen that won't flow the oil required.
Check out the rest of the engine too....as 500rpm difference is huge ! Did you do a compression check ? Does this engine have a lot of blowby ?
10-12-2011, 01:19 AM
#29
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500rpm difference ? Wholly crap! Pull it !
When checking the oil pump, don't forget to check the pick up tube for cracks and the pickup for a screen that won't flow the oil required.
Check out the rest of the engine too....as 500rpm difference is huge ! Did you do a compression check ? Does this engine have a lot of blowby ?
When checking the oil pump, don't forget to check the pick up tube for cracks and the pickup for a screen that won't flow the oil required.
Check out the rest of the engine too....as 500rpm difference is huge ! Did you do a compression check ? Does this engine have a lot of blowby ?
10-12-2011, 07:08 AM
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Just a thought: Very low oil pressure + hydraulic lifters @ higher rpm = power loss? (lifters bleeding down)
The scary thing is running the engine at high rpm at that low of oil pressure is at best dangerous!
The scary thing is running the engine at high rpm at that low of oil pressure is at best dangerous!
