Losing Oil Pressure

I still do not see a problem. 45psi under load and 30 hot idle is absolutely fine for a 5.7 chevy. If you told me 5psi hot idle, ok there is an issue.

If you are concerned about oil contamination from whatever, change the oil. That costs about 30bucks tops.

You can buy a mechanical test gauge 0-80psi or 0-60psi and a grease gun flex hose for less than it will cost to get a mechanic visit.

Greetings,
Mr. TB. Sorry. Incorrect use of the word journal. You changed the sending units but could the threaded hole the unit screws into in the block be gummed up or did you put anything on the sending unit threads that may be interfering with good electrical contact?

78puget-trawler said:

How many hours on these motors? 30 years is pretty old for a gas engine depending on service and hours on it.

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My old gages showed 685 hours each. I know they were supposedly rebuilt around 2007 I think. I dont know if these are the original hours. The gages sure do look original though. I bought the boat in 2012 or 13 with about 460 hours on each engine gage. That would mean the prev owners only put 460 on each engine in a period of 26 years. Not very much usage.

New Dash

Here is the old dash and the new dash. The new dash was not finished at this time. It was just sitting in place and the senders were not wired in yet nor were the mounting screws in yet.

I changed the layout somewhat. I did not like looking at one eng on one side and the other engine on the opposite side of the dash. I ended up (other than the tachs) putting like gauges adjacent to each other. That is oil next to oil, water next to water, etc. I favor my left side when driving so I put the oil and watergages on the port end of the dash. The 'unimportant' one like fuel and battery, on the starboard side. It's just the way I personally like to look at stuff. Now that everything is in place, All I have to do is get the lettering plates made up. Apparently, up here, the trophy shops cant seem to make what I want. They keep screwing it up. I gave them labels off a Dymo label maker I have and told them to duplicate except to add screw holes. They have the exact size and everything all set up for them. All they have to do is duplicate, and still screwed it up. Oh well. It's not that important now.

It doesn't do any good to change the sender if the fitting you're attaching the sender to is clogged from years of goo in there. And just putting on a new sender will likely just clog the new sender as well.

Rebuild at 460 hours sounds unlikely,so does 17 hours a year. I`d back the guages were zeroed at rebuild in 2007.
You report the readings gradually getting lower. Something is going on even if it`s gauge defect, and we rely on readings. Why not do the clean up cappy suggests and if not successful the test Ski recommends. Can you check the dash gauges themselves by swapping the connections between engines?

Ski in NC said:

I still do not see a problem. 45psi under load and 30 hot idle is absolutely fine for a 5.7 chevy. If you told me 5psi hot idle, ok there is an issue.

If you are concerned about oil contamination from whatever, change the oil. That costs about 30bucks tops.

You can buy a mechanical test gauge 0-80psi or 0-60psi and a grease gun flex hose for less than it will cost to get a mechanic visit.

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I'm with you on this. My Phoenix had 270 Crusaders with no oil coolers. At idle hot the oil pressure WENT UP to 75. Found VDO gauges with Teleflex senders made the gauges read backwards since new. New senders and the oil press dropped to about 8 coming off a hard run. They had 1500 hours on them when I sold it.
Relax OP.

The numbers are not bad but it is the change that would bother me. You could get a digital thermometer (Harbor Freight) and check the temperature drop across your oil cooler in & out oil hoses to see if there is a difference between the two engines. Check the in & out water hoses on the coolers too. This will tell you is both coolers are functioning the same (picking up the same amount of heat).
Oil pumps seldom fail, worn bearings account for most loss of oil pressure

"Recently. I had made a new dashboard with all instruments"

Was anything else changed, wired in or altered? Have you checked voltage on both engine gauge set ups? Are any other gauges (like temp) acting weird. Gut tells me it is not the engine getting ready to check out.

I know it's cumbersome to read all the previous posts before replying and I myself, dont either. Anyway, to reiterate......the problem started before the gauges were changed. At the time of changeover, the new gauges read the same as the old gages. I was hoping the the problem was that the old gauge faulty gauge but the new one had the same reading. The last time I took the boat out, the readings deteriorated RAPIDLY.
Tomorrow, I will pull the new sender off and the old low pressure shut-off.

1). If there is any clogging in the hole, what would be the best way to clean it?
2). When I buy a new mechanical pressure gauge and install it, can it be tested at the dock or do I have to take the boat out?
3). if I remember correctly, there is a threaded hole in the engine. Out of this hole is a "T". The sender goes in one hole in the "T" and the other hole has an object which I believe is a low pressure shut off. I think I have a new one laying around somewhere.

Keep in mind that I am completely lost when it comes to engines. It took me forever to find the old sending unit the first go around.

4).Maybe I ought to remove the "T" and just put the sender in the hole to see if I get a different reading without the low pressure shut-off involved?

The advice to try a mechanical gauge is really good and will give you a definitive answer whether you have a pressure or gauge issue. I really suspect there is a questionable connection somewhere, potentially in a terminal unknown to you. Your voltage probably drops slightly as your alternator is spinning slower, this would compound a high resistance in the circuit along with the natural nature engines running less oil pressure at idle. Again, a mechanical gauge will reveal what is really going on.

Greetings,
Mr. TB. IF you're going to test with the mechanical gauge (mg), I would take out the "T" and install the mg right into the block. After you take out the "T" and before you install the mg, make sure that threaded hole in the block is clear and not gummed up. Might also be a good time to make sure the "T" isn't gummed up as well.

I cleaned a sender supply passage by starting the engine with the sender out. Oil pumped out of course but that was the idea. Caused no problems just a mess as I only ran it briefly. I got lucky and all was well when I reinstalled the sender.
Your situation is different in that pressure lowers as oil heats up. I would follow the advice above and change the oil to see if that makes any difference.
Good luck.

The mechanical gauge is the best idea to confirm actual pressure. Most small blocks use the 1/8" pipe port that is near the base of the distributor, facing up. There are other places that can be used also, a port just above oil filter 1/4" pipe I think. If it makes you feel any safer, most performance engine builders use the rule of thumb: 10 lbs of oil pressure per 1000 rpms. So 30 lbs at idle is plenty safe, as long as it doesn't continue to drop. Checking and cleaning the oil passages in the block and fittings to the sending unit seems like a good idea.

Rafe

The other "object" is the low oil pressure alarm switch. It's what causes the engine alarm to sound every time you turn the key on before starting the engine

High Wire said:

The other "object" is the low oil pressure alarm switch. ......

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Yes, I thought of that also.

NEWS FLASH:

While walking the docks today, I ran into some Great Loop cruisers. One guy was waiting for parts for his tranny. We got in conversation about my problem also. Turns out him and his buddy are a bunch of old farm boys and have been working on engines all their lives. They offered to stop by and so they did.

I started engine while one guy stayed on the dock looking for oil in the exhaust water - non. After about 5 minutes or so, he came back on the boat. He looked for oil leaks in the oil cooler and found none. Then he took off one end of the fresh water cooling hose at the heat exchanger end and struck his finger up the hose feeling for any oily residue none. Then he checked the oil dipstick for any signs of gas in the oil - none. Then we restarted the engine and let it run for about 15 minutes. The gauge went from 55 down to 45 PSI and he didnt seem concerned. Then after a while he removed the valve cover and was inspecting the oil in there - it was wet with oil and he was convinced the oil pump was pumping. All the while they were listening to the engine and both agreed that all sounded really good.
Next, we started the other engine while the first one was still running. They were comparing the oil wetness and whatever from the Port Engine - the one we just started to the Stbd Engine (the one in question). Both were running and oiling exactly alike. By now, the Stbd engine was down to about 40PSI. they raised the throttle and the gauge went up some. After that they just listened and felt around. Their final prognosis: If it was their boat and they were planning to head out on a 1200 mile journey with little to no mechanics along the way, they both said that they would not hesitate to just go.
They would monitor the engine closely, but were not concerned about it.
That made me feel much better. These guys seemed to be as good of mechanics as anyone else around.

Right now, I have both engine room blowers running off the battery of the engine in question. It is reading 12V while the other is reading 12.5 V DC.
This does somewhat come into question and the other day was the first real
run of the boat since the new gauges. This made them question this item even though this was the same way before the gauge swap.

Anyway, I just back from Advanced auto with a mechanical oil gauge.
plans for tomorrow or Wednesday:

1). Remove "T" , check for any kind of blockage and then insert mechanical oil gauge directly to engine. Run engine if all is good, then I will test the sender alone and then with the tube and the low pressure alarm.
2). If all tests good, I will then swap the sender wires to test to see if the gauge is the problem.

Thanks for all of the great suggestions and please keep them coming.

The difference between people who have to press on with what they can figure out,....and many who have the luxury of waiting and paying for the option of least resisrance.

Check what you can, eliminate the obvious...take the average of the best advice you can get..,and roll your dice. It usually come down to that unless you or you mechanic are lucky and find something definitive early on.

It`s a great help and comfort going over the problem in person with someone else, with the engine running beside you. Not to say your TF friends are not a big help too. I hope it gets solved.

Tony B said:

2). ... I will then swap the sender wires to test to see if the gauge is the problem.

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You meant swap SENDERS port for starboard, right?

High Wire said:

You meant swap SENDERS port for starboard, right?

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Well, actually, I meant swap the wires under the dash, however, swapping the senders makes a lot more sense and is also easier to do.
Thanks.

BruceK said:

It`s a great help and comfort going over the problem in person with someone else, with the engine running beside you. Not to say your TF friends are not a big help too. I hope it gets solved.

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I know nothing about motors and never cared to learn. Well at 70 years old, I now wish I had. TF friends have actually been a great help. You guys have given me an understanding of what is going on and now I have the confidence to work on this stuff. When I changed the senders out, the new ones (Teleflex) looked nothing like the old VDO gauges. The old ones even has a ground wire. I had to ask someone to take a look and see if I was actually looking at a sender, LOL.

To answer an earlier question about good electrical contact, I noticed that some of the senders had pipe tape already wrapped on them - the tape started about 4 threads above the bottom. I just duplicated that to assure a clean contact area.

QUESTION:
1). After I install the mechanical gauge, swap senders or whatever, how long should I wait for the engine to cool down before removing and reinstalling that stuff. I figure the parts should be at the same temp. or do they equalize while installing.

2). I initially installed the senders with a cold engine and gave a snug fit plus a tad more. Without a torque wrench, about how snug or tight should they be?
I know the word 'snug' here is quite subjective.

Thanks in advance.

Greetings,
Mr. TB. You should be able to swap parts as soon as you can be assured you won't burn your fingers. Temperature has nothing to do with function. You're wise to ensure good electrical contact between sender and engine block by judicious application of tape. Pipe joint compound may be a better option rather than the tape but other members have used tape with satisfactory results.

Tightness? Just snug enough so there are no leaks. Goldilocks. Not too tight, not too loose, just right.

"Snug" is probably about right. Most guidance is between 10-13 ft/lbs so if you are using a 6" long wrench, push on the end your best guess of 20 lbs.


If the old unit had it's own ground wire, it didn't need to ground through the threads and the pipe tape didn't affect anything but the new unit does ground thru the threads and duplicating the old pipe tape usage would yield a poor electrical connection. A quick fix would be to clamp a grounded wire to the (unpainted) body of the sending unit with a hose clamp to hold it in place.

Is there a voltage stabilizer in this system? Some cars had them so the gauges always had the same voltage so readings would truly read what the sending units were doing. I still feel like this is a variable voltage issue. Conductivity changes with temp.

bilge53 said:

Is there a voltage stabilizer in this system?
............

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You may or may not be on to something and i doubt if there is a variable voltage stabilizer. here is the story....I recently traveled 350 miles down river.
In the past and up until my trip started. Both engines started up with 60 Psi or slightly better. The port engine (the good one) would drop down to a hair below 60 and stay there. The starboard engine (The engine in question) would usually drop down to about 55 and stay there. During the trip down, the starboard engine would then go down to about a little over 50 and stay there. So this was a new event, because the oil press never got that low before.
OK. that trip is over and the starboard engine has a new settling point of about 50 psi.

Now comes the new dashboard and and all new gauges and senders.
We took the boat out for a shakedown cruise before our next 650 mile trip we were planning for around Dec. 1. Both engines started around 60 psi which was normal. after a while the port (good engine) steadied out at 55psi which is it's normal. The startbooardd eng. the one in question, after about an hour or so went down to 50 and the slowly to around 40 (to the best of my recollection). I panicked and decided to head back to the dock. When we got there, I put the engines in idle for maneuverability and the stbd eng went down below 30. That has never happened before.
Now about the gauges. The old ones were VDO and the senders had ground wires. The new Teleflex gauges did not have ground wires but I was careful to pipe wrap tape several threads above the bottom to give me a good ground.
12vDC: The old gauges always read about 11.5 and sometimes down to 11V. The new 12V Port gauge, when engine running is now showing around 12.5 on the fly bridge, which I assume is correct and about normal. The Starboard gauge was showing 12.0 V because for some reason, both blowers are on the port battery and we always run with the blowers on. When I got back to the dock, it occurred to why the starboard eng batt showed on 12.0. I turned off the blowers and the starboard engine went back up to 12.5V, just like the other engine. It did not occur to me to check the oil pressure.

Also, we have an inverter and it ran the fridge and a few other things but that is on its own house battery supple. All of this is run through a battery isolator. Each engine has its own batt and the 2 house batteries have there own supply through the isolator.

Dont know if this is enough to make the gauges go gaga, but consider that it did not do this a few months ago and my stbd eng press was slowly going down even before the dash swap-out.

Thanks in advance.

Update: Not so good

Toay. I completely removed starboard (Problematic engine) oil sender and shut-off alarm and "T" and installed it in the port engine - the good engine. I was hoping I could nail this on the senders but not so. I ran the port engine for almost an hour tied to the dock at 16-1800 RPM which is about my normal cruising speed. The engine started at about 60 psi and went to about 53 PSI when I went to 1400 RPM. When I ran it up to and held 1800 rpm it steadied out at around 55 plus a tad PSI. The bad news is that the senders are fine.

Tomorrow, I will install the new mechanical oil press gauge in the starboard engine (Problematic one) and hope it works out fine. That will then narrow it down to an electrical problem. Which i just discovered - I'll talk about tomorrow no matter what happens with the mechanical gauge.

Wish me luck. and thanks again for all your help.

Excuse me if my question looks stupid to you but do you have the same oil grade in both engine?
Also while I am not a mechanic I do not think difference of oil pressure in two similar engine is a proof that something goes wrong. If you look at engine owner manuals you will have the range of normal running oil pressure and it my be quite large. For example, while my engine is pretty uncommon, the oil pressure range is going from 30 psi to 65psi. The manual indicate that 30psi at idle is normal but below that it is not and til 65psi at full speed is normal but higher it is not, and oil pressure depends on oil grade and oil temp.
Like mentionned by Ski in a previous post maybe 30psi at idle when engine is warm is not an indication that something is wrong.

Lou_tribal said:

.....do you have the same oil grade in both engine?
...........

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Yes same oil.

The problem is not in the number of psi, but rather the recent sudden drop.
If it dropped quickly from very good a month age and approaching the unacceptable level in a short time frame, I can only assume the down trend will continue. Something must is wrong somewhere totally regardless of what the other engine is doing.

Tony B said:

Yes same oil.

The problem is not in the number of psi, but rather the recent sudden drop.
If it dropped quickly from very good a month age and approaching the unacceptable level in a short time frame, I can only assume the down trend will continue. Something must is wrong somewhere totally regardless of what the other engine is doing.

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Another stupid question... Any oil leak anywhere on this engine? If the pressure drop it is obviously that the pressurized line (in or out the engine) has a leak. Any oil level decrease?

After swapping the senders, can you swap the wires to the gauges to see if it is a gauge fault?
I have a temp gauge which runs 30F above reality, as confirmed by an IR shot at the sender, it can happen.