Low Oil Pressure 350 Chevy

Mike Kulp · Post by **Mike Kulp** » Mon May 07, 2012 12:23 pm

I would remove sending unit and install good quality mechanical oil pressure gauge to verify 100% the actual oil pressure ( GM says 6psi at 1200 rpms is okay I think that is very low ), then I would drain the oil out of the drain plug to inspect quality of oil and for metal shavings, if no shavings may try high volume oil pump but it still could be bearing failure starting and oil pump may just cover it up for a year.

DAVIDLOFLAND · Post by **DAVIDLOFLAND** » Mon May 07, 2012 12:48 pm

Thanks guys,

The low oil pressure is confirmed by two seperate sending units.

All other engine performance indicators are normal.

Oil is changed twice per season, and is good and clean, however, I have not checked for metal particles.

Consensus is, there is a possibilty a weakening oil pump could cause the drop in pressure, so I'm gonna go ahead and change the pump to find out. It's just the start of our short boating season, so I don't want to start a re-power project right now, unless there is absolutely no choice. Gonna see if a new pump will let me limp through this season.

Thanks again for all the feedback,

Dave

Big D · Post by **Big D** » Mon May 07, 2012 8:28 pm

captainmaniac wrote:I am not really overly mechanically inclined, so I just look at symptoms to try to find patterns. Given that...

You say you have confirmed the problem is real - how? Are you dual station and pressure drop shows on both upper an lower gauges? Or have you used a manual pressure gauge? I am not trying to be a pita here... just to understand how you actually confirmed the problem.

Don't think you said what oil you are running (brand, viscosity), or what you are using for filters, or when the oil or filters were last changed, or how many hours since last oil/filer change.

I have seen people suffering from similar symptoms because of pickup tubes falling off, too much time between changes causing crud to block pickup tubes, too low a viscosity (though would have trouble seeing that on in Alaska!), too many additives, or overfilling causing foaming, without it being a problem with the oil pump itself.

Any other behaviour stuff - like is engine exhaust showing more smoke than normal, or more steam than usual? Sounds that weren't there before? The more info the real experts on this forum have, the better they are likely to be able to diagnose your underlying problem.

++1. I don't like the symptoms you're describing but proper diagnostics is needed before you start doing something that's not needed. Must most definitely confirm oil pressure with good test gauge at the engine. This will at the very least give you more accurate pressures. Remove any plumbing in place that your senders are hooked up to. If the switch and sender share the same plumbing ie off a â€œTâ€ fitting, they will both give a false reading if a problem exists in the fitting. I was ready to tear down an engine only to find a clogged fitting. The drops in pressure you describe though are pretty consistent with high pump component clearances and/or high bearing clearances. Do the above simple test, and have the oil analyzed as mentioned above, the analysis should confirm or eliminate the suspicion of wear. Lets cross our fingers.

mitch · Post by **mitch** » Fri May 11, 2012 1:29 am

mitch · Post by **mitch** » Fri May 11, 2012 3:09 am

akwalker · Post by **akwalker** » Fri May 11, 2012 5:28 am

mitch wrote:Low oil pressure after warm up.
1. bearings
2. bearings
3. bearings
Low oil pressure at all times
1. gears in oil pump bad
2. pressure relief spring in oil pump bad
3. bearings

++1

DAVIDLOFLAND · Post by **DAVIDLOFLAND** » Fri May 11, 2012 1:13 pm

'Hot idle' low oil pressure was confirmed with independent mechanical guage. No visible evidence of metal in oil or pan.

Agreed, oil pump is unlikley to be the cause (but some folks say there is a possibilty, as the spring can stick), but not the time of our short season to start a repower project. Willing to try anything short of a repower.

So, pulled the engine Tuesday, and removed the oil pump (2 hours), replaced the pump with a high volume pump, and re-installed the engine yesterday (5 hours). Started, warmed up, and pressure never dropped below 67 psi.

However, weather was 35 kts, gusting to 47 kts, in rain and snow, seas 4 ft (short, choppy four footers), so I did not take her out and really put her to the test, ie. run at fast cruise, then bring back to idle.

When the weather clears, I'll run her up, then let you guys know how she did. Good thing is, I'm in the repair less than 8 hours, and under $150. Now I just hope I did some good.

Mike Kulp · Post by **Mike Kulp** » Fri May 11, 2012 1:18 pm

Good luck I wish the best so you can get through the season.

mitch · Post by **mitch** » Fri May 11, 2012 1:22 pm

DAVIDLOFLAND · Post by **DAVIDLOFLAND** » Fri May 11, 2012 1:24 pm

I have not taken the old pump apart. I may do that, if indeed the new pump helps the oil pressure at hot idle.

mitch · Post by **mitch** » Fri May 11, 2012 1:24 pm

mitch · Post by **mitch** » Fri May 11, 2012 1:34 pm

hmc · Post by **hmc** » Fri May 11, 2012 3:52 pm

Mike Kulp wrote:Good luck I wish the best so you can get through the season.

x2

jefflaw35 · Post by **jefflaw35** » Fri May 11, 2012 4:14 pm

hmc wrote:
Mike Kulp wrote:Good luck I wish the best so you can get through the season.
x2

+3 cool picture too!!! good luck!!!

EM63 · Post by **EM63** » Fri May 11, 2012 5:29 pm

DAVIDLOFLAND wrote: So, pulled the engine Tuesday, and removed the oil pump (2 hours)

David - I love your strictly engagement

Some others of us are planning to move the engine about 3 weeks,
and you are doing this just in one sentence

THATS GREAT - my personal 'Trojan-boater-of-the-year'

--
Greetings - Heiner

PS: How did you get the engine out so quickly ???