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Old 02-06-2008, 18:10   #1
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Oil change causes oil pressure change.

Just did my first oil change, it was somewhat messy but I wiped it all up and hopefully the admiral will notice nothing... next time I'll be a lot neater!

Anyway, testing the motor afterwards she fired up fine and the oil pressure gauge hit 80 psi before returning after a few minutes to 60psi. Further running showed no further reduction and when I checked the oil levels it was still at the top dipstick marker.

Whats odd here is that prior to changing out the old black gunk the PSI would go off the scale on startup and settle to just under 80 psi after some running.

Something I should worry about? Double checking the two openings (oil fill on top and oil drain) they seem properly closed. There is no smoke on startup and the engine starts and sounds fine.
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Old 02-06-2008, 18:32   #2
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Its normal to have a higher oil pressure after an oil change. The viscosity of new oil is higher than that of worn out oil. As far as what is spec for your particular engine, your owners manual will tell you this. Its not too common but it could be the case that your pressure release valve is not working correctly. Check the owners manual first though.
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Old 02-06-2008, 18:47   #3
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As already stated, it depends on the grade and viscosity of the oil. Some diesels will also bypass after the oil clogs the filters to a certain degree. The pressure could possibly go up when this happens. A third factor to think about is that because of being in a marine environment, there is more moisture in the air. As you sart and shut off the engine, the oil can collect moisture that can mix with the oil. This can thicken the oil to the point to where there is more resistance in the engine causing higher oil pressure. In the furure, I would closely monitor the oil pressure. When it starts up, note how many hours are on the engine or how much calander time has past. Then back up to about 75% of than time and make that your regular oil change interval. Believe it or not, a boat that operates several hours a day can go longer hourly intervals between changes because the moisture is kept out by the consistant heat. Short heating and cooling cycles is very hard on engine oil. Synthetics are better for that, but still not perfect.
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Old 03-06-2008, 00:09   #4
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What I'm reading so far is "no the 15PSI drop since you did your first ever oil change isn't something to worry about too much".... actually I like the fact that now my engine is operating on the gauge rather than off the top of it provided when we next go out it doesn't drop further.

I like Hawk180's "back up to about 75% of that time" idea as it provides a yard stick that has some relation to the environment the diesel operates in (unlike "err just do it every 50 hours mate"). However is it safe to assume that the pressure will rise when the oil needs changing on *my* diesel?
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Old 03-06-2008, 01:37   #5
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My first question would be how old was the oil??
Hawk180, by the way, water actually does the opposite to viscosity. Yeah I know that it goes all gungy and waxy and so on, but the EP strength breaks down and the oil no longer has any "strength". Of course, that waxy gunge that can occur may block things like filter and/or other oil galleries.
Old oil can become very gummy and will take a lot more effort to get through filters and galleries and most importantly, the Relief Valve. This results in the pressure going high like you have seen.
If you take a look in the "Study Hall" at the start of this topic forum, you will read some good info on service intervals and why.
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Old 03-06-2008, 01:59   #6
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One good thing you can assume is that you are not getting excess diesel washdown into your crankcase which would dilute the oil and lower your oil pressure. Sounds like the old oil had thickened which can happen over time if not changed for a looong time. I think you solved your over pressure problem. Watching your oil and having an hour meter to change the oil at regular intervals will keep that from happening again. I use 100 hours as my change interval time. This has served me well on a wide variety of land based and marine based diesel engines over the last 30 years.
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Old 03-06-2008, 18:49   #7
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Quote:
Originally Posted by Alan Wheeler View Post
My first question would be how old was the oil??.... Old oil can become very gummy and will take a lot more effort to get through...
Hey Wheels I don't have any reference points beyond what I took out and what I put in - the difference being night and day. What I took out was black, gooey and nearly opaque. Pumping it out was noticably difficult despite the fact that I had run the motor for a few minutes to slick things up. If I were a betting man I'd say it was in the "pretty old" bracket.

Will be interesting to see how the new oil changes over the next hundred hours or so.
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Old 03-06-2008, 20:32   #8
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I would suggest that you run the engine hard for several hours under load and then change the oil/filter again. If the oil was that thick then there was probably quite a bit left that will mix with your new oil. Flushing that out could save your engine a lot of wear.
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Old 04-06-2008, 02:06   #9
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I agree. There are also some oil flush products available that could be worth shoving one through. The big danger is the the gum can block oil galleries and especially the ones to the cam shafts. This can result in scoring of the cam surface. the other area of concern is the piston rings. However, if it as a very old engine with very high hrs, sometimes that gum around the rings can be all that is holding the engine together. My view is that if the engine is that bad it's best to have the rings fail now than when you are out to sea and really need the engine.
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Old 16-06-2008, 15:10   #10
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Taking the advice to run the engine hard I opened up to 2500rpm yesterday (normally cruise at about 2000-2200) and within a few minutes the the temp had risen to 180f and the temp alarm went off (actually I wouldn't have noticed the alarm if I hadn't been watching the temp - note to self - replace!).

180f is within my operating range so either the temp alarm sender is miscalibrated or the temperature gauge. If the engine is overheating then I suspect the crimped elbow in the water heater extension to the coolant system as plenty of water was coming out of the exhaust. The alarm continued to go off even after backing off though the temperature gauge returned to normal pretty quickly. Kept me checking the old girl every five minutes...

Not really looking for answers here, just wanted to share the joys of being a noob with a new old boat One little operation leads to suspicious sender behvaior, alarm behavior, coolant behavior, perhaps gauge behavior and a slightly nervous GF - good thing I like this stuff! Other than the small alarm issue we had a great little nose around some potential weekending anchorages and a glorious sunny sail!
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