What should oil pressure be at 4000 rpm - Mercruiser 5.7-gctid383713

[Guest]

We usually keep the boat at 3000 ~ 3500 rpm max when out on the water. Usually the oil pressure is at or below 60 (from what I remember).

I had the boat on the trailer, muffs on, starting her up for the first time after sitting for the winter. I rev the engine to 4000 RPM and the oil gauge is far right at 80.

I tried a little bit of searching for Mercruiser specs, but all I could find was something running at 2000 psi

"Oil Pressure @2000 rpm 30-60 psi (207-414 kPa)"

Considering 80 is as high as the gauge goes, yet the tach goes to 6000 rpm (maybe higher if I recall), plus this other spec

"Maximum rpm @ WOT3 4400-4800"

I'm thinking maybe my pressure shouldn't have been that high? Would this go down if the engine had more time to warm up? I didn't start off at 4,000 rpm, but I also didn't let the engine idle for long at 2,000 rpm either.

[Guest]

My old racing rule of thumb was 10psi per 1000 rpm minimum; if you're seeing 30+psi at cruise, you should be OK.

[Guest]

2 things...when the engine and oil is stone cold...it's feasable to see 65+ psi at the oil gauge...

2nd thing...DON'T EVER CRANK THE ENGINE UP ABOVE 1200RPM WHEN ON MUFFS...

now you gotta change the impeller out.....

:arr arr

[Nikko]

seapuppy wrote:
2nd thing...DON'T EVER CRANK THE ENGINE UP ABOVE 1200RPM WHEN ON MUFFS...

now you gotta change the impeller out.....

Really? never heard this before - what's special about 1200 rpm? I've run up to 2500 rpm on many occasions either doing a pre-warm in the driveway, or flushing out after a salt water run, with many boats. Maybe I just have more water volume/pressure coming from my hose? On muffs I always check the temp of the water coming out the back - if it's luke warm - hot (but can keep your hand there), the volume is fine and the engine is getting what it needs.

With respect to the oil pressure, 80 psi is WAY too high and indicates an overfill of fluid (oil, or oil/water, or oil/fuel), a bad bypass valve, or a bad sender/gauge...

Check the easy stuff first -

Make sure the volume of fluid in the pan is correct and make sure it's just oil.

Add a mechanical gauge at the engine - they're handy to have anyways. this will tell you if you have a pressure problem or a sender/gauge problem.

If it's a real pressure problem, start researching the bypass valve. there's two - one in the oil pump itself (this is probably the bunked one) and one in the filter adapter (that keeps the high pressure away form the filter to prevent it from blowing apart).

If it's a gauge/sender problem - the sender's cheaper than the gauge- I'd start there.

Good luck - let us know what you find...

[Guest]

Nikko wrote:
Really? never heard this before - what's special about 1200 rpm? I've run up to 2500 rpm on many occasions either doing a pre-warm in the driveway, or flushing out after a salt water run, with many boats. Maybe I just have more water volume/pressure coming from my hose? On muffs I always check the temp of the water coming out the back - if it's luke warm - hot (but can keep your hand there), the volume is fine and the engine is getting what it needs.

With respect to the oil pressure, 80 psi is WAY too high and indicates an overfill of fluid (oil, or oil/water, or oil/fuel), a bad bypass valve, or a bad sender/gauge...

Check the easy stuff first -

Make sure the volume of fluid in the pan is correct and make sure it's just oil.

Add a mechanical gauge at the engine - they're handy to have anyways. this will tell you if you have a pressure problem or a sender/gauge problem.

If it's a real pressure problem, start researching the bypass valve. there's two - one in the oil pump itself (this is probably the bunked one) and one in the filter adapter (that keeps the high pressure away form the filter to prevent it from blowing apart).

If it's a gauge/sender problem - the sender's cheaper than the gauge- I'd start there.

Good luck - let us know what you find...

that's what the manual sez and it's a safety thing since the water supplied doesn't have near the volume of being in a lake or, river or ocean....

and I've seen on a stone cold engine almost 80psi on mine until the engine/oil warms up before....usually the pop off valve in hte oil cfilter will lift to relieve pressure.....so..not an issue....

once warmed up...the psi will run max at 55-60+/- psi.....

:arr arr

[Guest]

seapuppy wrote:
that's what the manual sez and it's a safety thing since the water supplied doesn't have near the volume of being in a lake or, river or ocean....

and I've seen on a stone cold engine almost 80psi on mine until the engine/oil warms up before....usually the pop off valve in hte oil cfilter will lift to relieve pressure.....so..not an issue....

once warmed up...the psi will run max at 55-60+/- psi.....

:arr arr

I will definitely keep an eye on the pressure the next time I get the boat back home and give it enough time to bring everything up to temp. I'm pretty sure, as you've stated, the pressure was only that high due to the temp.

[Guest]

do you have the manual for your engine/drive??...might wanna get it and check it out.....

:arr arr

[Guest]

I think you're just fine. I've owned 3 5.7's and I'm 10 mins from you. I don't mind swinging by and checking it with you.

[captharv]

Mine will hold 40 PSI +/- from about 1500 RPMs up. hey have a pressure bypass in the pump to provide a constant pressure, but the volume increase somewhat with higher RPMs.

1000 RPMs is about 35PSI

[Guest]

Robert K wrote:
We usually keep the boat at 3000 ~ 3500 rpm max when out on the water. Usually the oil pressure is at or below 60 (from what I remember).

I had the boat on the trailer, muffs on, starting her up for the first time after sitting for the winter. I rev the engine to 4000 RPM and the oil gauge is far right at 80.

I tried a little bit of searching for Mercruiser specs, but all I could find was something running at 2000 psi

"Oil Pressure @2000 rpm 30-60 psi (207-414 kPa)"

Considering 80 is as high as the gauge goes, yet the tach goes to 6000 rpm (maybe higher if I recall), plus this other spec

.

"Maximum rpm @ WOT3 4400-4800"

I'm thinking maybe my pressure shouldn't have been that high? Would this go down if the engine had more time to warm up? I didn't start off at 4,000 rpm, but I also didn't let the engine idle for long at 2,000 rpm either.

Robert, The factory stock gauges on production Bayliners are really only functional and their accuracy is probably about the same as most production cars. The only way to accurately measure oil pressure is with a top quality gauge. The aviation industry, for example, has a much higher standard of quality, and it is the old story, you get what you pay for. For example, our Bayliner was bought new and both oil pressure gauges do not read exactly the same. I know there is nothing wrong, except that the variation in stock gauges is probably normal. The only way to challenge an oil pressure issue is to install a high quality mechanical gauge. I hope this helps to understand some of the readings that we see in our production gauges, every boat is different, but for my case, I am not worried about a little variation. griff

[2850Bounty]

The SBC twin gear positive displacement oil pump hasn't changed much since 1955.



These and are capable of 200/300 psi..... possibly more.

Oil pressure control is a result of oil pump design, relief valve diameter and spring pressure. This should remain fairly consistent at all RPM once above idle.

Some experts and engineers will sugguest that ideal oil pressure (seen at the bearing journals) will be between 45-55 psi.

Any more pressure/volume in an engine that is not set up for it, can cause cavitation and oil suspension issues.

Most likely your oil pressure sending unit or gauge is faulty.

seapuppy wrote:
......... DON'T EVER CRANK THE ENGINE UP ABOVE 1200RPM WHEN ON MUFFS...

now you gotta change the impeller out.....

Steve, I believe that is a misnomer, and it is definitely a disclaimer by the OEM.

This risk may be a sustained RPM (while on the muffs).

Mechanics need to increase RPM to the Ignition TA limit RPM....... (often 3.2K rpm) in order to check ignition timing.

I do this routinely for short revs up to 3.2k rpm, and with zero issues. Merc or Volvo..... no problems.

It's a disclaimer... nothing more than that!

.

[Guest]

Thanks for all the suggesstions.

If you read my other post, I've got a blown altenator to replace. So until I get that fixed, the boat is simply gonna remain on the trailer at the storage yard. When I do get the alternator replaced, my next trip is to launch the boat and give it a good workout, staying close to the ramp of course

I'll let the engine temp come up to normal before I push it past 3,000 rpm and see what the pressure reading is then. If it is still hitting 80, then I will pursue some of the other options listed.

[Guest]

Robert, Ballard Electric can rebuild that alternator pretty quickly and for a good price.

[Guest]

griff wrote:
Robert, The factory stock gauges on production Bayliners are really only functional and their accuracy is probably about the same as most production cars. The only way to accurately measure oil pressure is with a top quality gauge. The aviation industry, for example, has a much higher standard of quality, and it is the old story, you get what you pay for. For example, our Bayliner was bought new and both oil pressure gauges do not read exactly the same. I know there is nothing wrong, except that the variation in stock gauges is probably normal. The only way to challenge an oil pressure issue is to install a high quality mechanical gauge. I hope this helps to understand some of the readings that we see in our production gauges, every boat is different, but for my case, I am not worried about a little variation. griff

Same with the senders... the senders get old and loose accuracy over time.

[Guest]

Mine, (a 5.0 Chevy), hits 70+at higher RPMs without difficulty. Hasn't blown up yet :worth.

That said, I've run my engine up to 4k RPM on muffs before, (hose on full blast), without issues, (I check the impeller every year...). Watching the water flow out the back, I still have some gushing out the sides of the muffs even at high RPMs, so I'm sure the engine is getting what it needs. I wouldn't leave it cranked to 4k RPM for very long, 30 seconds at most to check TAT, but still.