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1989 5.7 Cobra high oil pressure

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Falcon195

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Tonight while out running my boat with a 1989 5.7 cobra the oil pressure was reading as high as 70 to 75 psi at 3500 rpm and at idle speeds it was reading 40 to 50 psi. The engine was good and warm and the ambient air temp. was in the low 80's
It has always read 60 psi at 3500 rpm and around 35 to 40 psi at idle speeds.
The engine was good and warm and I am running Valvoline conventional SAE30 oil and the engine has almost 40 hours since the last oil change this past spring.
Also I use a oil additive called cam shield which increase the zinc phosphorus levels to acceptable levels for flat tappet cam protection that the new SM rated oils don't provide.
The oil filter is the correct Evinrude Johnson filter which was changed at the last oil change.
I know this could be a oil sender or gauge issue but I and a bit concerned since this just started to happen today.
Yesterday the oil pressure was normal.
Any ideas and other than a sender or gauge issue what could be causing this and what issues or problems could this cause?
Thanks
 
Give it a oil change. And change the filter. Maybe the bypass is clogged in the filter.

I use fram:..... is the correct numbers for your motor ph 13, ph 30, ph 5 ? < off the top of my head.
 
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agree - after you verify the reading with a mechanical gauge, give it an oil change and leave the additives out.

if you are concerned about zinc, send a sample of your new oil to the lab. don't just pour stuff in without knowing what levels are already in the oil.

The 30WT I use has almost 1000ppm zinc. adding more would be asking for trouble.
 
Thanks for the replies.
Changed the oil and filter today.
Verified today with a mechanical gauge and the readings are high.
Here is what I am getting with the mechanical gauge.
550 rpm = 45 psi
2000 rpm = 60 psi
3000 rpm = 65 psi
4000 rpm = 75 psi
Also the oil I am using has a SN rating which contains 800 ppm zinc.
The recommended amount of zinc for my engine and valve train are 1400 to 1600 ppm zinc.
I add 1/4 oz of cam shield per quart bringing my zinc level to 1400 ppm.
 
Falcon195 said:
The recommended amount of zinc for my engine and valve train are 1400 to 1600 ppm zinc.
Click to expand...
egads
no way. 800 is plenty.
600 is plenty... check the used oil when you change it, if over 300 you are fine

I suspect you have plugged that engine up with additives. hopefully pressure will settle down with just oil in there.
 
Alright i'm going to give it to you straight.

I know you want to do right by your engine and boat.

And i know you don't know me, but i hope you agree i only want to help you achieve your goal of doing right by your boat and engine.

So if i were you right now with what is happening with your engine i would drain about a quart of oil out of your pan.

Add a quart of automatic transmission fluid say atf III. Run the motor for a hour.

Drain the oil, and change the filter. Add the proper amount of 30 weight oil and run it for a hour.

Drain the oil and change the filter add the proper amount of oil 30 weight.

Go boating and enjoy watch the gauges.

DO NOT ADD ANYTHING OTHER THEN 30 WEIGHT OIL TO THE MOTOR AGAIN EVER.

Post back in a month of using the boat normally, on what the oil gauge is doing.

HAVE ANY OTHER ISSUES ?

Please post away we all here are ready to help.
 
it's time someone sued these snake oil companies. If your engine is done, you probably have a good case, but probably almost impossible to prove when the motor is over 20 years old. .

The thing is, that high oil pressure means that oil is not cascading out bearings like it is supposed to and I have to wonder what some of the cross drilled passages in the crank look like. I would be concerned about a spun rod bearing in the future. The rod bearings are last in line.

I don't recommend ATF in an engine - some ATF has additives that cause seals to swell. A leaking rear main crank seal wouldn't add any joy.
I might just flush it several times with some cheap 5W20 or whatever light oil.... just run it mid throttle -no load and then change it a few times... back to 30W, 20W50 or 25W40 finally. I'd probably stay with straight 30 because it has less additives in it than multigrades.
Hopefully the pressure will just return to normal with a few changes.
 
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I replaced the oil and filter today with straight 30 weight with no additives.
Just wondering if the there was an obstruction to one of the hoses that run from the valve covers to the flame arrester could that cause my pressure issues?
I did notice a slight amount of oil on the flame arrester coming from these hoses.
BTW would the pressures I listed earlier in this thread considered excessive?
 
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possible reason you are seeing oil coming out the breathers is because you may have clogged some of the drain passages from the head back to the oil pan- the valve covers are filling with oil more than normal.
But no, those vent hoses aren't even clamped on - can't build any pressure by clogging them - they would just pop off if clogged. or the dipstick will lift up to vent the crankcase... and that isn't what oil pressure is anyways....
see, that's what gets me..... it's fine to not have a great understanding of how an engine oiling system works as a boater...who cares.... but these products have people quoting zinc numbers like they are professional engineers....
Make sure your engine is getting up to temperature with a proper working thermostat (160F)
 
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Yes the engine temp is running at the correct range between 160 to 170 according to the gauge.
In fact since the water here is near 80 and the ambient air temp has been in the 90's the temp has been running closer to 170.
So engine temp shouldn't be a factor with my high oil pressure.
 
no, just wanted to be sure it wasn't running cold. cold engines can cause gunk to build up in oil drainback passages in the head.
 
Here is something interesting.
I just spoke to a local "reputable" mechanic and he told me that the manufacturers started to recommend running 40 weight oil in these engines and I should put 40 weight oil in my engine and that could fix this issue.
He said that in the warmer weather the 40 weight would run with lower pressure.
I explained to him that I thought that 40 weight would make the oil pressure higher and he said that it doesn't work like you would think.
Unless this mechanic has some kind of advanced insight I think I need to look elsewhere.
 
NEVER add anything to your oil other than more oil.
Run what the manufacturer suggests.They have been doing this for a whole lot longer than any of the people on here (sorry).
If it calls for a 5-30 then get the good stuff from an OMC/Merc dealer.
Or Mobil 1 synthetic or Penzoil or any good brand name..Use a good Fram filter.
If the guage is reading high then the sender/guage is going. The good thing is it's got pressure.
Check all the grounds and connections.
I worked on a NEW boat that the pressure was crazy.Up and down and all over the place(mech guage it was fine).Turns out the ground was pinched and not connecting right.
 
30 weight is still recommended.

And tell your mechanic bull 40 weight will cause the pressure to run higher.

And it will give more compression.
 
Falcon195 said:
I explained to him that I thought that 40 weight would make the oil pressure higher and he said that it doesn't work like you would think.
Unless this mechanic has some kind of advanced insight I think I need to look elsewhere.
Click to expand...
yep.... was he wearing tinfoil coveralls?
 
I have not added any additives so I don't know for sure what effect they can have on oil pressure. OMC recommended straight 30, Merc, 30 below 50* and 40 above, or a 25-40 that they sell, Volvo, straight 30 syn, or 20w-40 or 20w-50. This is for all the same basic GM base engines. So you can use any one of these choices, depending on temp. I have found that using straight 30 vs straight 40, the 40 holds hot idle press a bit better than the 30, but it's not a big increase. I run Chevron Delo 400 straight 40 in my 88 OMC 4.3 and hot idle after a run, at 600 rpm is about 20 psi, running it's about 50 or so. Cold fast idle is about 55, slow cold idle, 30-40.
There is a big difference in hot and cold pressures esp at idle speed.
I don't know how much zinc there is in the oil I use but since it's an old engine, I don't think it's a huge issue. The zinc issue from what I have heard is a bigger issue with high performance flat tappet engines with high lift cams and stiffer valve springs....
 
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