5.7 Merc Oil Pressure

[300sflyer]

Re: 5.7 Merc Oil Pressure

Got tired of hearing the alarm come on, so I pulled both engines from the boat. I figured I might as well pull both, and inspect the bearings on both of them while it was out of the water. The port engine bearings were fine, so all I did was put a new oil pump in it since the pan was off anyway. The starboard engine was another story... The front main bearing was toast, and the others all had some tell tail signs of metal in them... Luckey for me, the crank was still in good shape. I installed all new crank and rod bearings, [standard size] and a new oil pump. I decided to go with high volume pumps on both motors.

Once the engines were both installed and running again, I have about 70 PSI at 3800 RPM on the port engine, and about 75 PSI on the starboard engine when they are fully warmed up. [not WOT] Both show just under 40 PSI at idle. With new bearings in the starboard, I figure that is the reason for the slightly higher pressure.

I am wondering if those readings are a bit too high? Are there any possible problems that could turn up as a result?

Thanks!

 

[Eric 3.7LX Alpha 1]

Re: 5.7 Merc Oil Pressure

Got tired of hearing the alarm come on, so I pulled both engines from the boat. I figured I might as well pull both, and inspect the bearings on both of them while it was out of the water. The port engine bearings were fine, so all I did was put a new oil pump in it since the pan was off anyway. The starboard engine was another story... The front main bearing was toast, and the others all had some tell tell signs of metal in them... Luckey for me, the crank was still in good shape. I installed all new crank and rod bearings, [standard size] and a new oil pump. I decided to go with high volume pumps on both motors.

Once the engines were both installed and running again, I have about 70 PSI at 3800 RPM on the port engine, and about 75 PSI on the starboard engine when they are fully warmed up. [not WOT] Both show just under 40 PSI at idle. With new bearings in the starboard, I figure that is the reason for the slightly higher pressure.

I am wondering if those readings are a bit too high? Are there any possible problems that could turn up as a result?

Thanks!

So the starboard engine was the one with the oil pressure issue?

 

[300sflyer]

Re: 5.7 Merc Oil Pressure

So the starboard engine was the one with the oil pressure issue?

That is correct.

 

[joewithaboat]

Re: 5.7 Merc Oil Pressure

Got tired of hearing the alarm come on, so I pulled both engines from the boat. I figured I might as well pull both, and inspect the bearings on both of them while it was out of the water. The port engine bearings were fine, so all I did was put a new oil pump in it since the pan was off anyway. The starboard engine was another story... The front main bearing was toast, and the others all had some tell tail signs of metal in them... Luckey for me, the crank was still in good shape. I installed all new crank and rod bearings, [standard size] and a new oil pump. I decided to go with high volume pumps on both motors.

Once the engines were both installed and running again, I have about 70 PSI at 3800 RPM on the port engine, and about 75 PSI on the starboard engine when they are fully warmed up. [not WOT] Both show just under 40 PSI at idle. With new bearings in the starboard, I figure that is the reason for the slightly higher pressure.

I am wondering if those readings are a bit too high? Are there any possible problems that could turn up as a result?

Thanks!

Did you use an m55hv ? If so that is made for engines built with extra bearing clearance for turning high RPM.

75 PSI warmed up is an awful lot.

I think the filter bypass opens at 70 PSI to keep from blowing the oil filter, You could still perhaps blow it if you revved it up cold.

Did you check the crank for wear? Its pretty uncommon to have trashed the mains and not have worn the crank.

I would take a good look at the harmonic balance'r on that engine. That is usually what wipes out the front main.

It could also have a poorly clocked or spun front cam bearing, as the front main is oiled from above around the front cam journal.

 

[300sflyer]

Re: 5.7 Merc Oil Pressure

The pumps I put in are federal Mogul, with a 70 PSI pressure regulating valve. The crank was in excellent condition. The engine seems to run just fine, with no excessive vibration. I will have a good look at the balancer though. Thanks.

 

[joewithaboat]

Re: 5.7 Merc Oil Pressure

The pumps I put in are federal Mogul, with a 70 PSI pressure regulating valve. The crank was in excellent condition. The engine seems to run just fine, with no excessive vibration. I will have a good look at the balancer though. Thanks.

The pressure valve on the pump opens and lets some oil above 70 psi bypass the system and dump back into the pan. That is adjustable with a spring.

There is also a bypass on the filter adapter, that when open bypasses the oil filter. So when running with pressures that high you are not filtering the oil.

 

[300sflyer]

Re: 5.7 Merc Oil Pressure

The pressure valve on the pump opens and lets some oil above 70 psi bypass the system and dump back into the pan. That is adjustable with a spring.

There is also a bypass on the filter adapter, that when open bypasses the oil filter. So when running with pressures that high you are not filtering the oil.

Thanks for the info.

Below is the drawing of my remote oil filter assembly. Is this where the excess pressure would bypass the filter?

Also, here is a merc engine with a high flow 100 PSI pump. The RPM limit is 5200, which is not really much higher than my WOT RPM. I wonder how the bypass would work on this one, or would there even be one?

http://www.mercurymarine.com/repowe...ruiser-products/plus-series/383-mag-bravo-4v/

 

[joewithaboat]

Re: 5.7 Merc Oil Pressure

Thanks for the info.

Below is the drawing of my remote oil filter assembly. Is this where the excess pressure would bypass the filter?

Also, here is a merc engine with a high flow 100 PSI pump. The RPM limit is 5200, which is not really much higher than my WOT RPM. I wonder how the bypass would work on this one, or would there even be one?



http://www.mercurymarine.com/repowe...ruiser-products/plus-series/383-mag-bravo-4v/

I'm not sure....
I know that we would always plug the bypass on our racing engines in an effort to not have any unfiltered oil. This required running a HP series filter that is bigger and can flow 2x as much oil, with a burst pressure of 400psi. They are much heavier steel than a typical screw on filter. Every once in a while a customer would mistakenly put a standard filter on, which would usually blow up. These days everything now has all aftermarket remote cartridge type filters that are very high flow.

Maybe that 383 merc needs that 100psi pump to feed oil thru the external oil cooler and still have good return back to the engine??? Do you have that as well.

If you have already run these engines up to WOT and not ballooned or blown a filter Im betting there is a bypass somewhere. Some filters have an internal bypass as well.

 

[300sflyer]

Re: 5.7 Merc Oil Pressure

I'm not sure....
I know that we would always plug the bypass on our racing engines in an effort to not have any unfiltered oil. This required running a HP series filter that is bigger and can flow 2x as much oil, with a burst pressure of 400psi. They are much heavier steel than a typical screw on filter. Every once in a while a customer would mistakenly put a standard filter on, which would usually blow up. These days everything now has all aftermarket remote cartridge type filters that are very high flow.


Maybe that 383 merc needs that 100psi pump to feed oil thru the external oil cooler and still have good return back to the engine??? Do you have that as well.

If you have already run these engines up to WOT and not ballooned or blown a filter Im betting there is a bypass somewhere. Some filters have an internal bypass as well.

Don't have an external oil cooler. I have not been up to WOT yet with either engine, even before the bearing and pump change. I guess that is the next step. My hunch is the 70 PSI spring in the pump itself, has already kicked in at 3800, so WOT will not pose a problem. Guess I will find out this weekend.

 

[joewithaboat]

Re: 5.7 Merc Oil Pressure

Don't have an external oil cooler. I have not been up to WOT yet with either engine, even before the bearing and pump change. I guess that is the next step. My hunch is the 70 PSI spring in the pump itself, has already kicked in at 3800, so WOT will not pose a problem. Guess I will find out this weekend.

Keep us posted, id be interested in finding the location of the bypass in the merc system. It has to have one if that filter doesn't blow, because there is no way that little filter could handle a high volume pump at WOT. My biggest concern would be if your pressure is always that high, not just at cold start up, you are not filtering the oil.

 

[300sflyer]

Re: 5.7 Merc Oil Pressure

Keep us posted, id be interested in finding the location of the bypass in the merc system. It has to have one if that filter doesn't blow, because there is no way that little filter could handle a high volume pump at WOT. My biggest concern would be if your pressure is always that high, not just at cold start up, you are not filtering the oil.

Like I said, I think the 70 PSI spring in the pump itself has already kicked in, when I am above idle. Both engines are reading just below 40 PSI at idle, and the presure increases quickly as I advance the throttles. Perhaps someone else in the know, will chime in.

 

[Failproof]

Re: 5.7 Merc Oil Pressure

Even if the pump AND filter bypass are wide open, some oil will flow through the filter. The volume that the two bypass' possess combined are not quite as much as the volume the pump could potentially output. And as far as filtering, you could run no filter at all, just a bypass and the engine will last untill something starts wearing. Then metal will start building in the oil. We have OLD tractors, with thousands of hours, and no filters. On original engines still. Best thing you can do is monitor oil level AND CONDITION!

 

[joewithaboat]

Re: 5.7 Merc Oil Pressure

Even if the pump AND filter bypass are wide open, some oil will flow through the filter. The volume that the two bypass' possess combined are not quite as much as the volume the pump could potentially output. And as far as filtering, you could run no filter at all, just a bypass and the engine will last untill something starts wearing. Then metal will start building in the oil. We have OLD tractors, with thousands of hours, and no filters. On original engines still. Best thing you can do is monitor oil level AND CONDITION!

Right but old tractors, which i know almost nothing about, are probably inline engines which dont wear much, that turn low rpm, and have high oil capacity. I would bet money that there are kits to add filters to them.

 

[joewithaboat]

Re: 5.7 Merc Oil Pressure

Like I said, I think the 70 PSI spring in the pump itself has already kicked in, when I am above idle. Both engines are reading just below 40 PSI at idle, and the presure increases quickly as I advance the throttles. Perhaps someone else in the know, will chime in.

The spring in the pump has nothing to do with the system having or not having a bypass for the filter...

 

[300sflyer]

Re: 5.7 Merc Oil Pressure

The spring in the pump has nothing to do with the system having or not having a bypass for the filter...

Understood... However if the pressure from the pump never exceeds 70 PSI as I suspect, then there is no need for a separate bypass for the filter.

 

[joewithaboat]

Re: 5.7 Merc Oil Pressure

Understood... However if the pressure from the pump never exceeds 70 PSI as I suspect, then there is no need for a separate bypass for the filter.

I'm not a fluid engineer and dont pretend to have all of the answers but if you have 75 psi at your gauge when at 3,800 rpm hot, i would guess you will peg your gauge when cold. All this despite the pressure relief valve in the pump opening at 70 psi to allow some oil to flow back to the sump. If you take PSI readings from different locations on the engine you will see different #'s, i know because Ive had more than one gauge on numerous engines. You can also pump a pan dry with a high volume pump and standard sump capacity. I learned this the hard way.

If you look up the part numbers on the Wix site for Mercruiser applications that dont use a remote filter you will find that there is no bypass in the filter. This is because it is in the filter adapter at the block. Factory GM...

The filter for the remote mount does have a bypass built into the filter, probably why they cost 3x as much. You remove the factory gm filter adapter to hook it up.

Anyway back to my original point... at the pressure you are seeing the bypass will always be open limiting your filtering ability.
HV and or HP pumps are not intended for stock engines. Its not the end of the world and not like your engines are going to blow up or anything. I suspect that in most all factory applications only some of the oil is being filtered at any given time. I just get alarmed because i am used to running high flow filters and plugging the factory bypass or running a remote non bypass high flow forcing all oil to be filtered.

I would love to know what that merc 383, advertised to have a 100psi pump, shows for operating pressure. I bet it has a lot of bearing clearance.

 

[300sflyer]

Re: 5.7 Merc Oil Pressure

I'm not a fluid engineer and dont pretend to have all of the answers but if you have 75 psi at your gauge when at 3,800 rpm hot, i would guess you will peg your gauge when cold. All this despite the pressure relief valve in the pump opening at 70 psi to allow some oil to flow back to the sump. If you take PSI readings from different locations on the engine you will see different #'s, i know because Ive had more than one gauge on numerous engines. You can also pump a pan dry with a high volume pump and standard sump capacity. I learned this the hard way.

If you look up the part numbers on the Wix site for Mercruiser applications that dont use a remote filter you will find that there is no bypass in the filter. This is because it is in the filter adapter at the block. Factory GM...

The filter for the remote mount does have a bypass built into the filter, probably why they cost 3x as much. You remove the factory gm filter adapter to hook it up.

Anyway back to my original point... at the pressure you are seeing the bypass will always be open limiting your filtering ability.
HV and or HP pumps are not intended for stock engines. Its not the end of the world and not like your engines are going to blow up or anything. I suspect that in most all factory applications only some of the oil is being filtered at any given time. I just get alarmed because i am used to running high flow filters and plugging the factory bypass or running a remote non bypass high flow forcing all oil to be filtered.

I would love to know what that merc 383, advertised to have a 100psi pump, shows for operating pressure. I bet it has a lot of bearing clearance.

Lots of good info... Thanks!

I'm no expert either, however I would think that any pump with a max output of 70 PSI, would deliver no more than that regardless if the oil is hot or cold. The spring will give at 70 PSI, and would not know the difference. My gauge goes to 80 PSI, [assuming it's accurate] and I have not pegged it yet. The gauge sender is right on the block just above where the remote filter lines connect. A short run at WOT on the weekend will tell for sure.

I'm still a bit confused as to how the bypass on the pump works. Doesn't the excess oil simply dump back into the pan, without going through the filter? Thus all of the other oil travels through the normal passages including the filter before heading for all of the bearings and other places?

No idea on the 383. I just mentioned it as a comparison.

 

[300sflyer]

Re: 5.7 Merc Oil Pressure

Found this in my Merc service manual. Tons of good info here!

The engine lubrication system is a force-feed type. Oil is supplied under full pressure to the
crankshaft, connecting rods, camshaft bearings and valve lifters, and is supplied under controlled
volume to the push rods and rocker arms. All other moving parts are lubricated by
gravity flow or splash.

A positive displacement gear-type oil pump is mounted on the rear main bearing cap and
is driven by an extension shaft from the distributor (which is driven by the camshaft). Oil from
the bottom of the pump in the rear of the oil pan is drawn into the oil pump through an oil
pickup screen and pipe assembly. If the screen should become clogged, a relief valve in the screen will open and continue to allow oil to be drawn into the system. Once the oil reaches the pump, the pump forces the oil through the lubrication system. A spring-loaded relief valve in the pump limits the maximum
pump output pressure.

After leaving the pump, the pressurized oil flows through a full-flow oil filter. On engines with
an engine oil cooler, the oil also flows through the cooler before returning to the block. A
bypass valve allows oil to bypass the filter and oil cooler should they become restricted. Some of the oil, after leaving the oil cooler and/or filter, is routed to the No. 5 crankshaft main bearing. The remainder of the oil is routed to the main oil gallery, which is located directly above the camshaft and runs the entire length of the block. From the main oil gallery, the oil is routed through individual oil passages to an annular groove in each camshaft bearing bore. Some of the oil is then used to lubricate camshaft bearings. The remainder of the oil is routed to the valve lifter oil galleries and No. 1, 2, 3, and 4 crankshaft main bearings by means of individual oil passages which intersect with the annular grooves.
The camshaft bearings have holes which align with the oil passages or annular grooves in
the block and allow oil to flow between the bearings and the camshaft journals. The oil that
is forced out the front end of the No. 1 camshaft bearing drains down onto the camshaft drive
and keeps it lubricated.

The oil that reaches the crankshaft main bearings is forced through a hole in the upper half
of each bearing and flows between the bearings and the crankshaft journals. Some of the
oil is then routed to the connecting rod bearings through grooves in the upper half of the
crankshaft main bearings and oil passages in the crankshaft. Oil that is forced out the ends
of the connecting rod bearings and crankshaft main bearings and splashes onto the camshaft,
cylinder walls, pistons and piston pins, keeping them lubricated. Oil is forced out the
front end of the No. 1 crankshaft main bearing to assist in lubricating the camshaft drive. A
baffle plate, mounted on the bottom of the main bearings or in the oil pan, prevents oil thrown
from the crankshaft and connecting rods from aerating the oil in the oil pan.
Oil that reaches the valve lifter oil galleries is forced into each hydraulic valve lifter through
holes in the side of the lifter. From here, the oil is forced through the metering valve in each
of the lifters (which controls the volume of oil flow) and then up through the push rods to the
rocker arms. A hole in each rocker arm push rod seat allows the oil to pass through the
rocker arm and lubricate the valve train bearing surfaces. After lubricating the valve train,
oil drains back to the oil pan through oil return holes in the cylinder head and block.
The distributor shaft and gear is lubricated by the oil flowing through the right valve lifter oil
gallery. The fuel pump push rod is lubricated by oil thrown off from the camshaft eccentric.

 

[joewithaboat]

Re: 5.7 Merc Oil Pressure

The bypass in the pump essentially just connects the outgoing and incoming side of the pump so that the incoming oil is coming from the pan and the out going side of the pump. It doesn't actually dump excess back into the pan. It is also only so big so its not like it can regulate to a set pressure,it can only bypass so much..

 

[300sflyer]

Re: 5.7 Merc Oil Pressure

The bypass in the pump essentially just connects the outgoing and incoming side of the pump so that the incoming oil is coming from the pan and the out going side of the pump. It doesn't actually dump excess back into the pan. It is also only so big so its not like it can regulate to a set pressure,it can only bypass so much.

Again I'm no expert, however based on what the service manual states, I would respectfully disagree.

"A spring-loaded relief valve in the pump limits the maximum pump output pressure."

I'm going to contact the pump manufacturer, and try to confirm this.