Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Hello! Just bought this boat and after a short 15 minute run and then a short idle back, the oil pressure alarm went off and the oil pressure gauge showed almost 0. I pulled the dipsitck(which is obnoxiously long) out and the oil is very clean and full. No burning smell and no knocking sounds. Any ideas? Thanks in advance.

Chris

2001 Mariah Z275ST Center Cabin
6.2L Bravo III duo prop

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Could very well be the outdrive oil, not the engine oil. This is the next check, there is a reservoir for this near the transom somewhere near the rear of the engine compartment.

Someone correct me if I am wrong but this alarm is just as critical from what I understand.

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Actually, this is what the original owner told me and I didn't believe him! I might sound stupid right now, but doesn't the oil pressure gauge measure the oil pressure in the engine block?

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Someone much more educated than me should answer this, although what you said is true, there is still a low fluid level alarm for the drive fluid. I do not know if they are linked or separate completely, but they both exist.

If the previous owner alerted you to it, that may be a significant indicator to the fact that it had been low before and he refilled the fluid and the alarm went away???? I would definitely look into the drive fluid system and make sure it is all just right, there may be a loss of fluid from something not yet identified. First thing though is to fill and see if no alarm.

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

the oil pressure uses a sending unit on the motor and the oil pressure gauge. Before I got too worried I would try a manual oil pressure gauge on the motor. I'm not sure but a lot of low pressure alarms are based off the reading on the guage if the guage isn't being sent the right signal it will set off the alarm.

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

bought my z203 this past fall. first time out the oil alarm went off. found that the resi back of the motor just below minimum level. changed fluids and never came back.

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

The engine alarm can go off for any of the three systems it is linked to. Low engine oil pressure, engine overheating, or low oil level in the drive oil reservoir. Each has its own sending unit. These sensors can go bad, and give a false alarm. You need to find out which sensor is triggering the alarm, and if there is a legitimate reason for the alarm, or if it is just a defective sensor.

Check the drive oil reservoir first. If the oil is low, add some to the full mark. Next check the engine oil level on the dipstick. If your oil pressure gauge in the dash was indeed showing "zero" when the alarm went off, you have good reason for concern! You need to have the gauge and the oil pressure "gauge sensor" checked as well. [Yes, that is another sensor] It is quite possible you have more than one defective sensor.

When you are running the boat at cruising speed, what does the oil pressure gauge in the dash read?

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

My alarm would stay on, (so much that the previous owner disconnected the piezo!) When I found this out and reconnected it, and noticed the annoyance of the alarm beeping every 2-3 seconds, it turns out the drive lube reservoir sensor had gone bad. It's sold as one part with the reservoir, and it was about $46 at the Merc Service facility. Unfortunately I ended up paying over $450 in service and diagnostic costs to finally get it fixed. :eek_animated:

There's only 3 things on the alarm circuit, and all the sensors are easy to locate, they're the only tan wires with a blue line on them. Let us know what you find out!

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Chris -

You are correct about the oil pressure gauge on the dash - that measures the engine oil pressure and has nothing to do with the drive lube. I would figure that one out before I cranked the engine again. It is very possibly nothing more than a sensor or shorted wire but I wouldn't ignore it.

Three things will sound the alarm on your engine - low drive lube, low engine oil pressure or high engine temperature.

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Thanks for all the replies! I haven't been to the boat since last Sat. I am hoping to haul her home this weekend and then I can really take a look at the sensors and report back what I find. What test would you do on the sensors? Just a straight resistance check? Or watch for fluctuating voltage?

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Simple... First check the outdrive fluid level. If it’s low, bring it up to full. Next, run the engine with your garden hose and the muffs. [no higher than about 1200 RPM and drive lowered down] If and when the alarm goes off, pull the sensor wire off each sensor one at a time till you find out which one is triggering the alarm.

For the drive oil, there are two connectors on the bottom of the bottle. Just pull one apart. The oil pressure sensor is located just above the oil filter on the port side of the block. The high temp sensor is located on the thermostat housing. Both have a simple push on connector.

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Wow, it took me forever to find this old thread! Here is an update on this issue. Took the boat out yesterday and ran like a champ. When I came off of the throttle, my oil pressure would drop to zero on the gauge and the alarm would sound. I just replaced my oil sender unit a couple months ago. This is the first time the boat has been in the water since then. There were no knocking sounds and it was running fine. After a minute or so in the no wake zone, the pressure came back up. So then I started playing around with it to see. If I throttle down REALLY REALLY slow, the pressure would drop, but not all the way to zero. If I was at half throttle and came off throttle hard, it would drop but not to zero. Only when I was 3/4 to WOT and came off throttle, did it drop to zero. When it did drop to zero, I also tried putting it in neutral and revving it up. The pressure would go up as I revved up, but then drop right back to zero. Its like it just needs a full minute to relax and get back to pumping oil! I checked the oil sender to make sure the wire was seated on there correctly and it was. Oil levels are fine and oil was replaced when I put her up for the winter. I am really hoping it is not the oil pump....



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Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Hi Chris,
Not sure about your 6.2L but big blocks like my 7.4 MPI have a minimum spec of only 4 PSI of oil pressure at idle and a minimum of 30 PSI @ 2000 RPM. Have you tried putting a mechanical gauge on the engine to get a real reading? The sender/electrical gauge may not be accurately calibrated @ low pressures. If you truly had zero oil pressure the first thing you would hear are the lifters tapping and then the crank knocking.
Another thought - what type of oil are you running? If the viscosity is low, it may be heating and thinning out while you are at WOT...then takes a while to cool off and thicken up when in the 5 MPH wake zone. Since I am only a fair weather boater (above 50 degrees)...I only run straight 40 weight oil.
A third thought...is your oil level a little on the high side? If so, you may be getting some foaming of the oil while at WOT. It may take some time for the foaming to dissipate. I make sure to leave the oil level below the full mark. You could try sucking some out through the dip stick using an oil change pump and see if the process goes away. Just a thought.

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

Hey Steve! I use Mercruiser 20w-40 oil only. I haven't used a mechanical gauge to test. Unfortunately, I cannot recreate the issue on the trailer, so I can only test it while out on the water. I will see if a marina will rent that gauge or if I should just buy one.


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Oil Pressure alarm in 2001 Z275ST with 6.2L
 

I just brought my boat out for the first time this season. The alarm is going off. Had boat already serviced about a month ago and all fluids are good. Where are the sensors? So I can test which one is bad.

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

The oil pressure sensor is a bulb shaped sensor that screws into the side of the engine block. On mine, it is located on the port rear side of the engine just above the oil pan. It is a pain to get to. The temp sensors are located on your thermostat housing. I had 2 on mine. And the oil reserve sensor is located inside your outdrive fluid reservoir.


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Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

You might want to double check the outdrive fluid level first though.

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

is that the small reservoir on the port side just back from the motor?

Re: Oil Pressure alarm in 2001 Z275ST with 6.2L
 

That is where mine is located.