High Oil Pressure 80PSI

Dlcable

New Member
Jun 24, 2019
13
Long Beach CA
Boat Info
1985 SRV 300DB Sedan
Engines
Twin 260's
Hi,
I have a 1985 Merc 260 that spikes it's oil pressure at 80 PSI immediately after start up.
This engine also has an intermittent lifter tick that I assume is related. My guess is this lifter ticking and the 80 PSI is due to an oil passage blockage somewhere.
Fresh oil (10-30) and filter, nothing changed. I was hoping the blockage was in the oil filter.
I have not yet changed out the oil pressure sending unit but I guess that's my next step to make sure the 80PSI is not a bad reading.
Has anyone encountered this issue before?
 
Remove the oil pressure sender and screw in a mechanical pressure gauge.
 
Hi,
I have a 1985 Merc 260 that spikes it's oil pressure at 80 PSI immediately after start up.
This engine also has an intermittent lifter tick that I assume is related. My guess is this lifter ticking and the 80 PSI is due to an oil passage blockage somewhere.
Fresh oil (10-30) and filter, nothing changed. I was hoping the blockage was in the oil filter.
I have not yet changed out the oil pressure sending unit but I guess that's my next step to make sure the 80PSI is not a bad reading.
Has anyone encountered this issue before?

Everytime I have seen that, it has been a spun cam bearing
 
Hi,
I have a 1985 Merc 260 that spikes it's oil pressure at 80 PSI immediately after start up.
This engine also has an intermittent lifter tick that I assume is related. My guess is this lifter ticking and the 80 PSI is due to an oil passage blockage somewhere.
Fresh oil (10-30) and filter, nothing changed. I was hoping the blockage was in the oil filter.
I have not yet changed out the oil pressure sending unit but I guess that's my next step to make sure the 80PSI is not a bad reading.
Has anyone encountered this issue before?

While swapping out the sender, I would also try a mechanical gauge as a test, as Dennis has suggested.

Couple of questions:
1. Do you have a standard oil pump or HVP one?
2. How does the engine sound when running?
3. Before this was happening what was the "normal" oil pressure?

You will probably be better served if you swap the sending units between engines. This will prove the sending is bad if the problem switches engines.
 
Just a thought, I do believe your engine, as mine, calls for viscosity of 40wt, definitely not 30wt.
 
Lazy Daze - Yes, a mechanical pressure gage while or before swapping sending units fore sure.
El Cap - I had 10-40wt in it and just changed to 10-30wt to see if this might help the issue.
Skybolt - Standard oil pump as far as I know. I've owned the boat for 4 years and use it often. The engine sounds and runs great except for when the lifter is ticking. It goes away after a few minutes and the engine runs smooth again but I have not taken it up to higher RPMs as this oil pressure thing can't be good. The oil pressure has always been around 60-70psi when cold and approximately 40 psi when at operating temperature and under load.
Bill - I can absolutely see how a spun cam bearing would keep oil from flowing where it's suppose to and spike oil pressure. I would think there would be other issues like rattling sounds, knocking or something, no?
 
Lazy Daze - Yes, a mechanical pressure gage while or before swapping sending units fore sure.
El Cap - I had 10-40wt in it and just changed to 10-30wt to see if this might help the issue.
Skybolt - Standard oil pump as far as I know. I've owned the boat for 4 years and use it often. The engine sounds and runs great except for when the lifter is ticking. It goes away after a few minutes and the engine runs smooth again but I have not taken it up to higher RPMs as this oil pressure thing can't be good. The oil pressure has always been around 60-70psi when cold and approximately 40 psi when at operating temperature and under load.
Bill - I can absolutely see how a spun cam bearing would keep oil from flowing where it's suppose to and spike oil pressure. I would think there would be other issues like rattling sounds, knocking or something, no?

If your lifter ticking goes away when the engine gets warm, you are likely tinkering in the wrong direction with the oil (if it's related to the oil). The first number is the viscosity when cold, the second number is the viscosity when warm. If it was not ticking when warm on 10-40, you would expect to have zero ticking when cold if you switched to straight 40 weight oil.

That said, your engine probably wants 25W-40....I feel like Merc has been spec'ing this stuff since the day boats were invented :)
 
Thanks Stee - I get it, it's not an oil weight issue causing the 80psi reading. My guess is there must be a blockage someplace (or cam bearing like Bill said). There is no difference in the 80 psi reading or intermittent lifter tick after the oil & filter change.
My next step is to make sure the 80 psi reading is correct before doing anything else.
 
Not to get into oil discussion, but 15w40 was always good for my old big blocks at the time.

If your seeing oil pressure 60-70PSI then you most likely have an HVP oil pump. I would think it would pin the oil pressure when you first them up and they are cold. But if that isn't the norm then something else is going on.

I am still in the camp of swapping the oil senders and see what happens, if the problem switches then it's your senders.

If there is something blocking the oil gallery it's already too late. Your not going to save anything by babying it. I would at least rev it up at the dock to ~1200 or so and let stay there for a few minutes and see what happens. How does the engine sound. If there is oil not getting to something the damage is already done, end a new long block is instore.
 
Was it always like that or is it something you just noticed
 
Oil pressure is controlled by the pressure regulator/relief valve. If this engine is a traditional cast iron chevy based engine then the pressure regulator/relief valve is located as a part of the oil pump which is mounted on the rear crankshaft bearing cap. It will bypass oil back to the oil pan when it reaches it opening pressure. So, a high oil pressure condition means the poppet is either sticking or has some debris in it.
 
Try using a motor flush, cant hurt at this point
 
Oil pressure is controlled by the pressure regulator/relief valve. If this engine is a traditional cast iron chevy based engine then the pressure regulator/relief valve is located as a part of the oil pump which is mounted on the rear crankshaft bearing cap. It will bypass oil back to the oil pan when it reaches it opening pressure. So, a high oil pressure condition means the poppet is either sticking or has some debris in it.
As a note if, in fact, the pressure bypass valve is not functioning correctly and you are seeing real high oil pressure at idle conditions there is a very good chance the distributor drive will snap off - then you'll have a bigger issue.
 
Oil pressure is controlled by the pressure regulator/relief valve. If this engine is a traditional cast iron chevy based engine then the pressure regulator/relief valve is located as a part of the oil pump which is mounted on the rear crankshaft bearing cap. It will bypass oil back to the oil pan when it reaches it opening pressure. So, a high oil pressure condition means the poppet is either sticking or has some debris in it.

That is a common reason. The oil filter drain back valve (assuming it has one) can also be defective preventing from oil flowing in the correct direction. I have seen it happen.
 
I put a mechanical oil pressure gauge on the motor this weekend and the oil pressure is fine so I ordered a new sending unit. I guess the intermittent lifter tick is an unrelated issue.
Thanks to all who responded to this thread!!
 
Glad you got it handled
 

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