Low oil pressure at 4000 RPM ???????
12-28-2011, 08:22 AM
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Low oil pressure at 4000 RPM ???????
OK guys, back at it and still no answers.
I have a 38 Formula with NA 540's based on GenVI blocks. Profiler heads, Comp Cam, GM hyd rollers, 12 qt Wet sump, Melling high volume std pressure pump, MSD ignition, 950 cfm carb, Eagle rotating assy, .0028" bearing clearance.
Oil temps only run about 225 HOT. Both engines run about the same temps.
Put the boat in the water last spring with fresh engines, both sound good, seem to run good, oil pressure about 55-60 PSI off idle, warm. At about 4000 RPM, the starboard engine loses oil pressure to about 20PSI, then hangs there above 4000. Bring it back down below 4000, and it will slowly build back to 55 psi. Figured it was the gage, so I ran it all summer. Before taking out of the water, I checked with mech gages, and saw the same low pressure.
Now the engine is on the stand. I checked the trap door in the pan, it is free. Bearings look good. Oil pump pick up is about 3/8" off the pan floor. Oil pump has some minor scratches on the case and gears, but nothing drastic. The pump drive shaft seems to only have about 1/8" engagement, but does not show any signs of slippage. The distributor gear does show a large amount of wear on the teeth, and will need to be replaced.
So far I have seen nothing that would cause the oil pressure issue. I would like to hear any suggestions on where to look. Unless I get that "ah-ha" moment, I will not trust putting the engine back in the boat.
Thanks
I have a 38 Formula with NA 540's based on GenVI blocks. Profiler heads, Comp Cam, GM hyd rollers, 12 qt Wet sump, Melling high volume std pressure pump, MSD ignition, 950 cfm carb, Eagle rotating assy, .0028" bearing clearance.
Oil temps only run about 225 HOT. Both engines run about the same temps.
Put the boat in the water last spring with fresh engines, both sound good, seem to run good, oil pressure about 55-60 PSI off idle, warm. At about 4000 RPM, the starboard engine loses oil pressure to about 20PSI, then hangs there above 4000. Bring it back down below 4000, and it will slowly build back to 55 psi. Figured it was the gage, so I ran it all summer. Before taking out of the water, I checked with mech gages, and saw the same low pressure.
Now the engine is on the stand. I checked the trap door in the pan, it is free. Bearings look good. Oil pump pick up is about 3/8" off the pan floor. Oil pump has some minor scratches on the case and gears, but nothing drastic. The pump drive shaft seems to only have about 1/8" engagement, but does not show any signs of slippage. The distributor gear does show a large amount of wear on the teeth, and will need to be replaced.
So far I have seen nothing that would cause the oil pressure issue. I would like to hear any suggestions on where to look. Unless I get that "ah-ha" moment, I will not trust putting the engine back in the boat.
Thanks
12-28-2011, 08:34 AM
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i have heard several people on this sight wiht the similar problems. seems the most common culprits are:
1) oil level in the engine is too high causing the crank to cavitate the oil in the pan.
2) a blockage in the oil system. ie. oil cooler blockage or a pinched/collapsed line.
1) oil level in the engine is too high causing the crank to cavitate the oil in the pan.
2) a blockage in the oil system. ie. oil cooler blockage or a pinched/collapsed line.
12-28-2011, 09:25 AM
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i have heard several people on this sight wiht the similar problems. seems the most common culprits are:
1) oil level in the engine is too high causing the crank to cavitate the oil in the pan.
2) a blockage in the oil system. ie. oil cooler blockage or a pinched/collapsed line.
1) oil level in the engine is too high causing the crank to cavitate the oil in the pan.
2) a blockage in the oil system. ie. oil cooler blockage or a pinched/collapsed line.
12-28-2011, 09:40 AM
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First and most important thing for you and all readers of this post to remember is that with only one engine having this problem it becomes a little more obvious that the build spec on the parts and set up of the engine is not the problem because the problem is only showing up in the starboard engine only.
The wear on the distributor gear is possibly because the camshaft may be a hardened billet with a hard alloy gear cut from the billet of the camshaft. If this is the case a special material distributor gear will have to be used to stop this gear wear. The other engine should have the distributor gear checked also as it may have the same problem. this problem is most likely not the reason for this big drop in oil pressure as the port engine has no real oil pressure problem. This gear wear is a problem though as the metal debris from this excess wear is moving throuhout the engine causing problems in other areas.
The oil pressure dropping above 4000 rpms indicates that something on this engine is most likely shutting off or reducing oil flow to the oil pump and causing a pressure drop. This is backed up by the fact that on teardown you are not seeing bearing wear, damage or other obvious mechanical issues.
Do both engines have the same , dip sticks and tubes,windage trays, pans, oil line plumbing,oil filter assemblies, oil coolers, etc.? If the oil systems are identical than I would suspect the problem may lie in a possible oil routing restriction, oil filter internal breakup or collapse, etc. You can carefully cut open the filter and check its internals. Also look carefully at the oil pump pressure relief valve on the pump and make sure its not sticking, galled in the bore or piston or has a broken or bad oil relief spring.
On the Gen 6 blocks the oil pressure relief valves used and number installed (either 1 or 2) can have an effect depending on how the remote oil filter -cooler system is routed. Check again to see if both engines are assembled identically on this item.
Just some checking items and suggestions here, but there has to be a logical reason for one and not both engines to expierence this problem.
Good luck on your investigation and search.
Best Regards,
Ray @ Raylar
The wear on the distributor gear is possibly because the camshaft may be a hardened billet with a hard alloy gear cut from the billet of the camshaft. If this is the case a special material distributor gear will have to be used to stop this gear wear. The other engine should have the distributor gear checked also as it may have the same problem. this problem is most likely not the reason for this big drop in oil pressure as the port engine has no real oil pressure problem. This gear wear is a problem though as the metal debris from this excess wear is moving throuhout the engine causing problems in other areas.
The oil pressure dropping above 4000 rpms indicates that something on this engine is most likely shutting off or reducing oil flow to the oil pump and causing a pressure drop. This is backed up by the fact that on teardown you are not seeing bearing wear, damage or other obvious mechanical issues.
Do both engines have the same , dip sticks and tubes,windage trays, pans, oil line plumbing,oil filter assemblies, oil coolers, etc.? If the oil systems are identical than I would suspect the problem may lie in a possible oil routing restriction, oil filter internal breakup or collapse, etc. You can carefully cut open the filter and check its internals. Also look carefully at the oil pump pressure relief valve on the pump and make sure its not sticking, galled in the bore or piston or has a broken or bad oil relief spring.
On the Gen 6 blocks the oil pressure relief valves used and number installed (either 1 or 2) can have an effect depending on how the remote oil filter -cooler system is routed. Check again to see if both engines are assembled identically on this item.
Just some checking items and suggestions here, but there has to be a logical reason for one and not both engines to expierence this problem.
Good luck on your investigation and search.
Best Regards,
Ray @ Raylar
Last edited by Raylar; 12-28-2011 at 09:43 AM.
12-28-2011, 10:01 AM
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Thanks Ray.
Both engines are identical spec. They both have identical dipsticks, windage trays, etc.
I will check the oil bypass valves. I know that there is only one in the engine losing oil pressure, it is the one on the flat area of the oil filter pad. I intentionally left out the one under the oil filter nipple.
I will further dis-assemble the oil pump and check the pressure relief plunger.
Both engines are identical spec. They both have identical dipsticks, windage trays, etc.
I will check the oil bypass valves. I know that there is only one in the engine losing oil pressure, it is the one on the flat area of the oil filter pad. I intentionally left out the one under the oil filter nipple.
I will further dis-assemble the oil pump and check the pressure relief plunger.
12-28-2011, 02:04 PM
#6
Please please please keep this post going till you find the answer. I chased the identicle problem for 2+ years till I finally installed a new crank and oil pan. The problem went away but I see nothing wrong with the ones I pulled out. Wasn't oil lines as I ran a filter directly off the block, no difference. Ran two quarts low, no diff. replaced oil pump and bearings, no diff, tried multiple guages, no diff. I sure hope you find the answer and send me a reply!
Good luck
Good luck
12-28-2011, 04:47 PM
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I can add a bit more detail.
Thhe engine was originally built by a pro shop. It went into detonation or something and lost a couple pistons. I bought a NEW GM block, Eagle rods, H bearings, GM roller lifters, SRP pistons & rings and timing chain. Turned the crank, cleaned the oil cooler and lines. Re used cam, manifolds, carb, oil pump, distributor, sheet metal, and all other hang on stuff. Point being, the problem was not there on the original motor, so the answer is somewhere other than oil level. I am not bragging, but I am an engineer in charge of designing engines. And my hobby is building high perf engines. I am not new at this (Just say'n). This has me stumped. Everything looks good. What am I missing here.
Thhe engine was originally built by a pro shop. It went into detonation or something and lost a couple pistons. I bought a NEW GM block, Eagle rods, H bearings, GM roller lifters, SRP pistons & rings and timing chain. Turned the crank, cleaned the oil cooler and lines. Re used cam, manifolds, carb, oil pump, distributor, sheet metal, and all other hang on stuff. Point being, the problem was not there on the original motor, so the answer is somewhere other than oil level. I am not bragging, but I am an engineer in charge of designing engines. And my hobby is building high perf engines. I am not new at this (Just say'n). This has me stumped. Everything looks good. What am I missing here.
12-28-2011, 09:55 PM
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12-28-2011, 10:45 PM
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DOC, a friend of mine had a similar issue on a new build[new block]just about drove him crazy,it ended up being the lifter bores,they were oversize from the factory,he had them bored&bushed,problem went away.with loose bearing clearance,plus loose lifter bores,a lot of oil is leaking internally.
