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Old 11-20-2016, 07:43 PM   #1
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Losing Oil Pressure

I have twin Crusader 270 engines - 350 Chevy Block.

Heading down from Knoxville, Tn. area I noticed my stbd engine which normally held Oil Pressure at about 55 psi, started slowly losing pressure.
Recently. I had made a new dashboard with all instruments and on short play trips of about 3 or 4 hours i noticed that it was getting lower. We were giving the engines a good run the other day because we are planning to head further south. My starting oil pressure is the old 55 -60 PSI. After about an hour or so it dropped down to about 50 and then to about 45. In idle it dropped below 30.

I tried to find a reliable mechanic but they are hard to come by. One was supposed to come by today but never called or showed.

Until he finally gets here, I am in a panic. My oil seems clean, there is hardly any smoke, I'm not using any oil and the engine seems relatively quiet and runs smooth.

Anyone have any idea what this could be?
I'm in panic mode, not just because of the expense of repairs, but also, If we dont leave soon we will probably have to stay till spring.

Thanks in advance
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Old 11-20-2016, 07:55 PM   #2
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45 running and 30 at idle is fine for a 5.7 chevy. Does not matter if it was 55 at cooler temps. It takes a long while for oil temp to stabilize and as it heats up, pressure will drop. That does non mean there is a problem. Especially that some 5.7's have no oil cooler. You can shoot the oil filter with an IR gun and if under say 220F, you are ok.

Do check oil on stick for any signs of water or if level increases due to fuel dilution. Also check under oil fill cap for mayonaisse or milkshake.
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Old 11-20-2016, 08:21 PM   #3
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..........45 running and 30 at idle is fine for a 5.7 chevy. Does not matter if it was 55 at cooler temps...... You can shoot the oil filter with an IR gun and if under say 220F, you are ok.

Do check oil on stick for any signs of water or if level increases due to fuel dilution. Also check under oil fill cap for mayonaisse or milkshake.
My other engine starts with about 60 PSI and drops to about 55 PSI. I would think that the engines should be close to each other. Also, the engine in question had this sudden drop while the other pretty much stayed the same.

There does not seem to be any water in the oil at the dip stick. I will check under the oil filler cap and use my IR on the oil filter. I will get back to you in a few days. Thanks
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Old 11-20-2016, 08:22 PM   #4
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I'm with Ski on this one. The Chevrolet small block is a very simple engine, not at all hard to deal with. The oil pressure will drop as the oil heats up. At cruising speeds the oil pressure is regulated by a spring loaded relief valve that's built into the oil pump. It isn't very sophisticated, just a spring loaded plunger that keeps the pressure from going sky-high when the engine speed (and oil pump speed) picks up.


Newer engines run at lower oil pressures - 40 is common and they last forever. This improves vehicle fuel mileage a little. Higher oil pressure is not necessarily better.


I'd second Ski's advice about monitoring for fuel or antifreeze in the oil, and checking your oil every day before starting up. As long as you do that, the chances of a failure in your oil system is very low - this oil system has been in production for more than 60 years now and there's none better.


That's my story and I'm sticking to it.


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Old 11-20-2016, 08:31 PM   #5
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It's normal for psi to drop as the oil heats. You do need to know hot hot it's getting. Above 200 it starts losing lube qualities. If you're running the engines hard you may need oil coolers.
Some things that help are cooling fins on the oil filters. Oil filters come in different sizes for the same engine block. Some manufactures put short filters on, but the longer versions allow the oil to flow thru the filter slower, cooling better along with catching more dirt. Filter catalogs show the thread, diameter and length. A remote oil filter cools more. Another issue could be how hot your engine room becomes.
Chevy engines have a high volume oil pump available.
Some old slow marine diesels only have 5 psi at idle.
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Old 11-20-2016, 08:34 PM   #6
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Gauges and especially sending units can and do fail. The first thing to do is connect a separate, mechanical gauge to the engine to verify the oil pressure. The reading you get with a different gauge will dictate what you need to do next. If the mechanical gauge shows good pressures, then you know the problem is the sending unit, wiring or gauge. If it turns out the presssure is actually falling during a run, there are at least a couple of issues that can cause that. One is if the oil level is too high. The oil can get whipped up by the crankshaft and the resulting oil/air mix will have lower pressure. Another possibility is if the engine has a mechanical fuel pump. The pump diaphragm could be leaking and gasoline could be diluting the oil.

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Old 11-20-2016, 08:35 PM   #7
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Sounds like a gauge issue not a true oil pressure problem. A bad connection in your guage wire will get worse over time as it heats up. It sounds like both engines are doing the same thing. I would check for a bad ground.
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Old 11-20-2016, 08:37 PM   #8
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These are Crusader engine packages - they come with well designed oil coolers.


I too, once thought that "normal" oil temps were south of 180 F. However, since the early '90s, Caterpillar has been engineering engines with oil temps as high as 240. I had a pair of sixteen cylinder engines that ran 240 and when I sold them they had 80,000 (eighty thousand) hours on them. ...so much for the conventional wisdom...


So, I wouldn't fret about it unless they're significantly hotter than Crusader recommends.


Onward!


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Old 11-20-2016, 08:38 PM   #9
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Though the current reduced pressures may still be in spec, it`s the change that calls for investigation, even if it`s only a gauge reading issue.
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Old 11-20-2016, 08:44 PM   #10
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Greetings,
I think Mr. TB has explained this is a NEW and sudden phenomena. One engine has changed while the other has remained "normal". Both are subject to the same environment (hot ER). So my question is, other than a gauge malfunction, what could be causing this?
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Old 11-20-2016, 08:53 PM   #11
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My concern is not so much the lower reading as the fact that this is happening quickly. We are ready to embark on a 1200 -1400 mile trip and dont want to have the pressure keep dropping. A mechanic was supposed to show up with a mechanical gauge but he didnt make it. The engine is 30 years old. and the water temp never get above 160 - 165 Till he gets here, I have a few questions:
1). If the problem is the oil pump, how difficult/costly is it to get it repaired/replaced?
2). I know what water/anti-freeze looks like in the oil and I see no signs of this. How can I tell if gasoline is getting into the oil?
3). If I take IR readings in the slip, how long should I run the engines and at what RPM should I run them at to get a decent reading? 5 min? 10 min? 20 min?
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Old 11-20-2016, 08:55 PM   #12
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Greetings,
other than a gauge malfunction, what could be causing this?
Sending unit failing, clogging up. Thus the other suggestion of using a separate gauge to confirm the issue. The other telltale alarm is 'the new instrument' panel. Sounds like a whole lot of wire disconnections, and reconnections to chase.

Disconnect the gauge and reconnect it directly using short wires along side the engine. that way you eliminate the wiring, and other issues of the 'new panel' installation. If it doesn't clear up, swap gauges. see if the problem follows the gauge.
If that doesn't help then find a 0-80 pressure gauge and hook it up directly to the oil pressure sender plug. This way you completely bypass the oil pressure sender, wires and existing gauges.

There are actually oil pressure filters that screw into the hole, then the oil pressure senders screw into them. The gunk in oil can clog up the sending units over time mimicking what you are describing. Make sure the issue isn't a 'false' reading, before it is a failure of oil pump issue.

Change the oil filter first. They have an oil pressure bypass shunt. Do cheap stuff first.
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Old 11-20-2016, 08:58 PM   #13
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Greetings,
I think Mr. TB has explained this is a NEW and sudden phenomena. One engine has changed while the other has remained "normal". Both are subject to the same environment (hot ER). So my question is, other than a gauge malfunction, what could be causing this?
Thanks
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Old 11-20-2016, 09:00 PM   #14
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1). If the problem is the oil pump, how difficult/costly is it to get it repaired/replaced?
2). I know what water/anti-freeze looks like in the oil and I see no signs of this. How can I tell if gasoline is getting into the oil?
3). If I take IR readings in the slip, how long should I run the engines and at what RPM should I run them at to get a decent reading? 5 min? 10 min? 20 min?
1) you have to pull the oil pan.. if that's possible in your bilge, after you get the pan off, its about five minutes. However, my opinion, probability of problem, in order is: gauge, overheating, main journal bearings, oil pump.

2) Smell and viscosity - very obvious.

3) Under no load.. kind of indefinitely - oil will never get to same temp as it does under load.
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Old 11-20-2016, 09:07 PM   #15
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Sending unit failing, clogging up. Thus the other suggestion of using a separate gauge to confirm the issue. The other telltale alarm is 'the new instrument' panel. Sounds like a whole lot of wire disconnections, and reconnections to chase.
The problem started to manifest itself before the instrument change. When the new panel and instruments were installed, the readings on the new oil gage was identical to the old gage at the time of the swap-out. Most of the wiring was simple daisy chain stuff and verified along the way. There were only about a dozen sending wires total, maybe less. They were carefully labeled and also verified by color code on the schematic. Also most of the readings were either dead on or close the the old gage readings. The only readings that were different the fuel tank readings and the battery readings. The battery readings are similar as to what my multi-meter reads and the fuel tanks, I dont really care about. I use a dipstick. And now, my tachs are steady and not wandering all over the place
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Old 11-20-2016, 09:14 PM   #16
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The problem started to manifest itself before the instrument change.
I still would not rule out sender/gauge. Have you tried swapping sending units? Or getting a known good mechanical gauge?

EDIT: Also.. previous comments re: acceptable range are spot on too.. even if not gauges.. is there really a problem here?
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Old 11-20-2016, 09:16 PM   #17
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Do you still have the old gauge? If so, install it down next to engine, using clean well connected wired directly to the sending unit. see if you get the same 'falling' readings. If you do, then pull the sender out and try to clean the nozzle end (the inside which would get the oil pushed up against it).

Think about it this way. The oil sender unit is at a dead end of a short pipe in the block. ANY oil having been pressured up doesn't 'go anywhere' to get flushed out. It is common to have oil 'gunk' collect on the grainy pressure sensitive ends of the senders and they get clogged. It's not like it gets a 'wash' of oil past it, which in turn gets filtered. I've taken several out over the years and it's like a dirty sludge covered oil nozzle. Short money on removing the sender, cleaning it with spray on brake fluid cleaner (or just swishing around in a cup of gas) and letting dry then reinstall.
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Old 11-20-2016, 09:19 PM   #18
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Greetings,
Mr. TB. Mr. k makes a good, easy, cheap suggestion. If I recall, the sending unit on my 350 is quite accessible...
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Old 11-20-2016, 09:30 PM   #19
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I am currently in Kev's camp. Swap sending units. Maybe clean the passage into the engine with stiff fishing line or brass wire prior to installation of senders.
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Old 11-20-2016, 09:35 PM   #20
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I am currently in Kev's camp. Swap sending units. Maybe clean the passage into the engine with stiff fishing line or brass wire prior to installation of senders.
Q-Tips work wonders.
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