Oil Pressure Problems

I'm throwing one other thing out. I am also having shifting issues where sometimes when docking and I shift in forward it thinks it is in neutral and last week when I put it in reverse and then neutral it stayed in reverse even thought the throttle was locked in in neutral. Have read that the shift interruptor switch can cause alarms and am wondering if that could be my issue here. Anyone else have this issue?
 
No interuptor switch on a Bravo. Even on an Alpha, which has one, no alarm.

You only have alarms for drive fluid, oil pressure, high engine temp. You mentioned something about a knock sensor - but I don't know about that one.

If fluid is good (and is the Merc High Perf stuff), the shift cable is likely on it's way out. There is an adjustment that can be done with a special tool, but the lower cable probably will need to be replaced.
 
B3's don't have shift interupters. Worn, corroded lower shift cable is more likely your problem.

Speakerdude has is right, that only 3 systems can trigger an alarm on your boat, or a grounded wire

Disconnect each system, 1 at a time, to figure things out.
 
RonG said:
Thanks all for the advice. I agree I think it is an intermittent electrical issue. I cleaned the oil pressure sender contacts and it was pretty corroded and green. Couldn't find the oil pressure switch to check that out. Dennis if you can give me a clue where that is it would be greatly appreciated. I assume it is near the sender and believe it is a blue/tan wire but couldn't find it.
Click to expand...

on my 1998 5.7 the oil pressure sender and the oil pressure switch were both screwed into an extension fitting on the port side of the engine block....the sender is screwed in at 90* to the extension fitting and the switch is screwed in the end of the fitting...the sender has a single blue wire and the switch has a purple wire and a purple/white wire....in my research concerning oil pressure sending units i found where other 5.7 engine have the oil pressure switch installed at the remote oil fiter and some have it installed near the distributor....i guess different years of 5.7 engines had different wiring layouts....

good luck...

cliff
 
Ron, can you verify with your mechanic regarding the knock sensor causing the alarm to sound? I was over at the shop and I asked one of our tech's about that. He mentioned that the if the knock sensor is acting hinky it would show up in the ECM's history, but it won't sound the alarm. I'm curious if there's more to this than myself and our tech know about?

And, I agree with Scof that you could disconnect the sensors. The only thing I'd do differently is to disconnect two sensors at a time and wait to hear the alarm. The reason for this is that you would positively ID the problem sensor. If you disconnect one sensor and you don't get an alarm, it may just be coincidence that the problem sensor picks this timing to not be flaky.

Actually, even better is wait till the alarm sounds and disconnect one sensor at a time until the alarm stops.
 
Yes I will ask him. Now that you mention it I don't see anything written anywhere where a knock sensor causes an alarm. That is a good idea to disconnect one or two at a time and see if I get an alarm. The only issue is in the past it would alarm like every 5 times out so maybe Dennis' idea of waiting for the alarm and then disconnect each one is the way to go. I just have to find that oil pressure switch. Cliff gave me some places to look. I'll also have to locate the temp alarm switch. During past alarms I have tried disconnecting the lube oil bottle sensor connections and that didn't stop the alarm so kind of gave up on that as the culprit. Thanks for your continued interest and help everyone.
 
Between what Cliff said and what I said, you should find the oil pressure switch pretty easily.

The water temp switch is pretty hard to get to... it's the one in the t-stat housing with the two wires. The single-wire one goes to the gauge.
 
Update - had the mechanic read the alarms and plug in a pressure gauge. Alarms were confirmed to be oil pressure. Dennis, by the way i did ask him if the knock sensor could cause alarms and he said yes at certain rpms. I havent seen that in any of the literature but who knows. The pressure gauge read the same as the dash gauge so I guess at least I know that is working fine. So he said the oil pressure is low at idle. It reads about 27psi at first idle and then after heating up for a while it idles around 15 to 20 psi. At load it is pretty much solid at 40 psi. So here are my questions for you guys who have similar engines....

what is your oil pressure at load, first idle and then idle after it has been run for a while under load?
how would you know if you had an oil pump problem? Can an oil pump have intermittent issues or just die?

So my next steps are to replace the oil switch, change oil and filter and run this thing until it dies. If I continue to get alarms I will disconnect the alarm. any advice from you folks are certainly welcome.

Thanks all!
 
Mine runs at 20-25psi cold or hot idle at cruise runs at 45psi constant I have 900hrs on it has run that way since we bought it at 384hrs. According to the merc manual all 5.7l, 350 & mx6.2l oil pressure should be 30-60psi @2000rpm at idle min 4psi. I think 4psi is way to low for any kind of comfort level. I think I'd ask another mercruiser certified mechanic about the knock sensor throwing an alarm.
 
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Bob & Sue said:
Mine runs at 20-25psi cold or hot idle at cruise runs at 45psi constant I have 900hrs on it has run that way since we bought it at 384hrs. According to the merc manual all 5.7l, 350 & mx6.2l oil pressure should be 30-60psi @2000rpm at idle min 4psi. I think 4psi is way to low for any kind of comfort level. I think I'd ask another mercruiser certified mechanic about the knock sensor throwing an alarm.
Click to expand...
Thanks for the info. That is fairly consistent with what I am seeing. On the knock sensor he said it would not cause the same alarm as the oil pressure but could cause a secondary or non-critical alarm. Anyway that's not important to me. I am more convinced I don't have a real engine issue but some other intermittent electrical issue or maybe an oil pump issue.
 
I can't recall what my exact pressure numbers are off hand. But I seem to think that while at "planing speeds" it runs around 40psi. I do think it drops down at idle, once warm, as well. I just can't remember where it drops to. Keep in mind that "40psi" is read off the dash gauge, so it may not be entirely accurate.

I would not be concerned (at least at this point) about your pressure numbers. They are WELL above what is required by the engine for safe operation. The best thing you could do is to simply monitor it and look for drastic changes. A few psi lower during one outing doesn't necessarily mean it's going south for the winter. It might be right back up again the next outing. Monitor the changes over time and see what's going on.
 
the oil pressure on my 5.7 with approx 500 hrs stays between 40 - 50 psi all the time.......

cliff
 
Thanks Dennis and Cliff for your responses. Dennis if you think about it next time you're out I would be curious to know what your gauge says at cold idle, under load and at hot idle. Interesting that Cliff's doesn't change at all at idle versus load.
 
Sure, no problem Ron.

What oil are you using (and Cliff, as well, if you're reading this)?

I use the regular Merc 25-40.



EDIT: Sorry, didn't mean to exclude anyone. Anyone else that responds to Ron regarding what your pressures are, if you could also state what oil you are using, that would help.
 
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I just got back in from being out all day I looked at my pressure readings at startup 40psi @ 1000 rpm after it starts to warm up to 130 deg 30 psi at 700 rpm gets to 170 40psi at 1000 rpm at 700 rpm 30 psi, running at 3200 rpm 45 psi for 20 minutes brought it back to idle 25 psi at 700 rpm ran for 6 hours today coming down a no wake zone for 1 mile to dock 1000 rpm 30 psi at dock 700 rpm 25 psi . I run mercruiser synthentic 25-40 914 hrs on it.
 
Lazy Daze said:
Sure, no problem Ron.

What oil are you using (and Cliff, as well, if you're reading this)?

I use the regular Merc 25-40.
Click to expand...
I haven't changed my oil since picking this boat up from the dealer at the beginning of the season. So I really don't know what they used unfortunately. I'll call them to find out what they use.
 
Bob & Sue said:
I just got back in from being out all day I looked at my pressure readings at startup 40psi @ 1000 rpm after it starts to warm up to 130 deg 30 psi at 700 rpm gets to 170 40psi at 1000 rpm at 700 rpm 30 psi, running at 3200 rpm 45 psi for 20 minutes brought it back to idle 25 psi at 700 rpm ran for 6 hours today coming down a no wake zone for 1 mile to dock 1000 rpm 30 psi at dock 700 rpm 25 psi . I run mercruiser synthentic 25-40 914 hrs on it.
Click to expand...
Cliff thanks for all the info. This looks very similar to mine but yours seems about 5 psi above mine at all the conditions you reported which is no big deal. I have about 570 hours on mine and hope I can get to 914. The good news is I really think the motor is fine and running normal and probably have an electrical issue with the alarms. I plan to change out the oil pressure switch to see if that stops the alarms. Probably should change oil/filter as well.
 
Lazy Daze said:
Sure, no problem Ron.

What oil are you using (and Cliff, as well, if you're reading this)?

I use the regular Merc 25-40.




EDIT: Sorry, didn't mean to exclude anyone. Anyone else that responds to Ron regarding what your pressures are, if you could also state what oil you are using, that would help.
Click to expand...

me too....i use the Merc 25-40....

cliff
 
RonG said:
Thanks Dennis and Cliff for your responses. Dennis if you think about it next time you're out I would be curious to know what your gauge says at cold idle, under load and at hot idle. Interesting that Cliff's doesn't change at all at idle versus load.
Click to expand...


my oil pressure gauge was not working for most of this boating season until i recently replaced the sending unit.....the 40-50 psi i posted earlier is what i have observed when working on the boat at home on the trailer and using a garden hose for water supply....to be honest i don't remember what the pressure reading was before when the boat was in the water and running under load, but i do know that low oil pressure was never a concern for me....i plan to run the boat this w/e on the lake so i'll watch the pressure and report back next monday.....

cliff
 
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