89 mercruiser 4.3 oil pressure drops around 3500 rpm

peatsaman

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May 24, 2011
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Hi, I have a 89 Rinker with a 4.3 mercruiser in it and the oil pressure is great till I get around 3500 rpm then the gauge jumps around a little then goes down to zero. when I slow down it jumps back up on the gauge. I never hear any knocking in the engine when it goes down but don't keep it going that fast that long. I'm just wondering if it could be the sending unit or something much more expensive internally. Thanks
 

Don S

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Re: 89 mercruiser 4.3 oil pressure drops around 3500 rpm

Could be a sender, or a gauge. Seems odd that it would do that only at rpm. Is it repeatable?

Have you checked the oil level? If over full, you could be getting aerated oil from the crankshaft hitting the oil.
 

peatsaman

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Re: 89 mercruiser 4.3 oil pressure drops around 3500 rpm

It does it just about every time out. No i haven't checked the oil but i will, had it changed at a shop so I assumed it would be correct but you never know i guess.

Once i get up to 3500 rpm or over it starts doing that. other wise it runs perfectly.

Thanks for reply I will go check the oil level to see if thats the problem
 

Don S

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Re: 89 mercruiser 4.3 oil pressure drops around 3500 rpm

It does it just about every time out. No i haven't checked the oil but i will, had it changed at a shop so I assumed it would be correct but you never know i guess.

Once i get up to 3500 rpm or over it starts doing that. other wise it runs perfectly.

Thanks for reply I will go check the oil level to see if thats the problem

Never assume anything like that. You should check the oil, (and a few other things) every time you take the boat out. Includes looking at the engine when in the water to make sure everything is as it should be.
 

peatsaman

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Re: 89 mercruiser 4.3 oil pressure drops around 3500 rpm

I checked the oil and it looks to be overfilled by a lot, however its sitting on a trailer on uneven ground. I'll check again when I get it in the water. Hopefully that's all it is.
Thanks for the help
 

Don S

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Re: 89 mercruiser 4.3 oil pressure drops around 3500 rpm

Just adjust the trailer tongue jack so the engine is level, and check the oil.
 
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