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I took the boat for a spin this morning before I have to go to work. I looked at the oil pressure gauge and it looks to high. It's an original so my first thought that it's inaccurate. But I don't know.

At idle, it indicates 40psi. At cruise, 3000rpm, it is indicating 65 to 70psi. Is that normal? I don't remember paying attention to the gauge before but this seems to high.

The past two tank fulls of gas have shown an increase in the burn rate. .7g/hr increase. It's not a lot but with a possible high pressure reading......I don't know.

Thoughts?

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That pressure seems high. The easiest way to check is to connect a mechanical guage at the engine. You can pick one up at an auto parts store for about 15 deer. If that shows the pressure is OK, then you have to check out the electrical one on your engine. The most likely culpit is the sending unit. You might simply just buy a new sending unit, put it in, and see what your guage reads. If your pressure reading on a mechanical unit is still high, then you've got to investigate as to why. There are a few possible causes and trouble-shooting would be needed. Hy

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Oil pressure for your engine should be listed in engine tune up specs in engine service manuals. Procedure for testing of oil pressure gauge and sender is there as well. You can get free service manuals from link in my signature.

Mercruiser Service Manual #9 says 30-55 PSI @ 2000RPM for your engine.

Check section 4D for instruments troubleshooting.

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Thanks for the specs. I'll check this out. Assuming that the gauge and sending unit are correct, what are the causes of high oil pressure and what damage can happen if not taken care of?

As a comparison, I took my Trans Am for a spin this morning. Gorgeous morning for a ride. I went up to Niagara Falls [caught a rainbow off the mist] then into N Tonawanda for breakfast.

It is a 6.6L engine and as I cruised around, I watched the oil pressure gauage. The average indication was 41psi at idle and averaged a little over 60psi above 60mph. At 3000rpm it was closer to 65psi.

Next time I take the boat out, I'll watch the gauge at 2000rpm. Haven't found my tester yet. I know I have one somewhere.

It would have been a great morning to take the boat up the Niagara River. It was like glass.

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Oil pressure for your engine should be listed in engine tune up specs in engine service manuals. Procedures for testing of oil pressure gauge and sender is there as well. You can get free service manuals from link in my signature.

Mercruiser Service Manual #9 says 30-55 PSI @ 2000RPM for your engine.

Check section 4D for instruments troubleshooting.

I just did a quick look at the manual. Can't thank you enough. This is more important than an owners manual. I may not have the experience to actually do most of the stuff listed, but at least I'll be educated while someone else is working on it.

My brother obtained something similar with the Bronco which is stored on the other computer. The program is so old it won't download into my computer. I'm certain my brother would have loved this "e-manual." He liked to do the work himself.

Thanks.

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Thanks for the specs. I'll check this out. Assuming that the gauge and sending unit are correct, what are the causes of high oil pressure and what damage can happen if not taken care of?

As a comparison, I took my Trans Am for a spin this morning. Gorgeous morning for a ride. I went up to Niagara Falls [caught a rainbow off the mist] then into N Tonawanda for breakfast.

It is a 6.6L engine and as I cruised around, I watched the oil pressure gauage. The average indication was 41psi at idle and averaged a little over 60psi above 60mph. At 3000rpm it was closer to 65psi.

Next time I take the boat out, I'll watch the gauge at 2000rpm. Haven't found my tester yet. I know I have one somewhere.

It would have been a great morning to take the boat up the Niagara River. It was like glass.

what are the causes of high oil pressure

Some engines run that high, but that seems excessive for yours.

causes could be any of the following:

1. Recent oil change with oil that is too heavy (50 weight)for temperature (but pressure will usually drop as oil gets hot)

2. Stuck pressure relief valve in the pump

3. Spun cam bearing

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I took the boat out today and watched the gauge. At start up [cold] the needle jumped to over 65 and remained there for a while. Eventually, it settled down to about 55 regardless of the throttle setting. Idling was about 45. I'm thinking that the gauge is working but just not accurate. I will still have it tested just to make sure.

What is that blue thing....Mercathode.

I pulled the engine cover today. I snapped a picture for all to view. The first comment out of my dad's mouth was, "That engine sure looks busy."

Merc350.jpg

I am to assume that the oil filter is the one on the left? If so, what is the filter for on the far right? Also, can I assume that the temperature senser is in between the pulley/water pump and the hose?

You wanna try and change my spark plugs on THIS engine? :haha-7383:

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Never Assume! Far right is the oil filter (Remote Location) the filter on the lower left under the mercathode is the fuel filter. The mercathode is in simplest terms a large circuit breaker that controls all electrical power to the engine and drive system. It is also an important part of the galvanic isolation system that prevents electrolosis from destroying your outdrive. Read the repair manual you will learn alot. :)

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Never Assume! Far right is the oil filter (Remote Location) the filter on the lower left under the mercathode is the fuel filter. The mercathode is in simplest terms a large circuit breaker that controls all electrical power to the engine and drive system. It is also an important part of the galvanic isolation system that prevents electrolosis from destroying your outdrive. Read the repair manual you will learn alot. :)

You are 100% correct on the filters, and the Mercathode being an "anti-galvonic" device that reduces corrossion on the outdrive unit but emitting a small electrical charge from the anode atached to the drive unit. But is has zip to do with controlling engine / accessory power. That's the job of the circuit breaker (the red reset button right by it.)

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I own a 256ssi with a Volvo 5.7 L engine. At idle the oil pressure is 40 psi. At random Times while operating the pressure spikes at the 80 psi mark. If I drop the revs down I usually lower the pressure to 40 again. I have changed oil and filters with not change in this pattern for almost 2 years.

I guess it can be a stock pressure relief valve of bad sender? Would either be a problem that would damage the engine. The boat seems to run fine. The dealer has not been able to identify the issue.

Thanks

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Much depends on the year of your 256 SSi. If you have the round analog gauges, then my first guess would be the oil pressure sender is NFG. If you have the square digital style gauges, than I would say your tachometer or the multi-fucntion guage is euchered.

MerCruiser recently brought out a newer style oil pressure sender for analog gauges made by VDO. Seems to be a quality piece vs. the standard issue sender that has been around for decades.

Believe it can be found under the port side exhaust manifold on that engine. Almost certain that the sender has puked if you have analog (round) gauges. Highly recommend replacing with 8M0068784, which is a new style sender sold by Mercury. Made by VDO. Higher quality piece IMO. NOTE: believe Volvo uses the same sender.

Original style (painted black of course)

815425T_zps3878470d.jpg

New style - a little smaller in size than the older style

8M0068784_zps0ba33d66.jpg

Here's a test sheet of what you should see when you ground the single sender wire from the oil pressure sender itself to the engine block, with the key in the 'on' position.

Gaugetesting.jpg

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I Just bought a 1996 2335 Chap with the 7.4 454

At Idle it is 40 psi and at 3500 rpm is bout 65-70 psi

Seems high to me, but it runs fine.

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