Low Oil Pressure 350 Chevy

jddens · Post by **jddens** » Fri May 11, 2012 5:45 pm

I had the exact same symptoms on the engine I had rebuild last year. Fine pressure cold at idle, OK at any RPM over 1000 when warm.......next to nothing warm at idle......

Upon tear down we found that the #3 main bearing had spun. Before I pulled the engine I verified the pressure reading using a know good mechanical oil pressure gauge. It's easy to check on the 350, the sender is right by the distributor at the rear of the block.

I also had the oil analyzed and they found metal bearing material.........

I hope this isn't the case for you, it wasn't an inexpensive repair.............

Good luck........John

DAVIDLOFLAND · Post by **DAVIDLOFLAND** » Fri May 11, 2012 8:49 pm

Thanks Heiner,

Bid D's title is well-deserved by him, but thanks for your kind thoughts.

The main reason the engine came out so quickly is, when I installed them 8 years ago, I used anti-seize compound on everything. So, 8 years later when I had to pull an engine again, not a single frozen bolt. I swear by that suff.

Plus, I kept my lift frame / I-beam / trolley / chain-hoist set-up, so it took less than 10 minutes to put that back up, an hour and half disconnecting stuff, then up comes the engine. Slick.

EM63 · Post by **EM63** » Fri May 11, 2012 8:56 pm

David - do you have some more pictures ???
Please

--
Greetings - Heiner

Big D · Post by **Big D** » Fri May 11, 2012 9:07 pm

DAVIDLOFLAND wrote:....Bid D's title is well-deserved by him....

Thanks buddy. Thinking about you a lot today. Hope it all works out. Keeping my fingers crossed and eagerly awaiting the sea trial results.

DAVIDLOFLAND · Post by **DAVIDLOFLAND** » Fri May 11, 2012 9:47 pm

Thanks Big D,

Sea trials tomorrow, if the weather lays down.

Here's a picture of me and and the engine, when we were both 8 years younger. I think the engine is holding up better than me. I need to shave. Lost my razor while the wife's outta the country for a couple of months.

Picture shows the hoist set-up.

Big D · Post by **Big D** » Fri May 11, 2012 10:09 pm

Nice set up. We were all younger 8 years ago. That doesn't look like dryer vent hose

DAVIDLOFLAND · Post by **DAVIDLOFLAND** » Sun May 13, 2012 2:26 pm

Sea trial results...

New HV oil pump did not cure the hot idle pressure drop, but it did add some pressure. Now, returning to idle after fast cruise, I'm getting almost 10 psi, vs. near zero before the pump change.

If I'm careful, this should allow me to get through this season, and I have the summer to think about repowering this winter.

Gonna start a new post, for feedback on that subject.

Thanks again for all the replies to this subject.

prowlersfish · Post by **prowlersfish** » Sun May 13, 2012 5:41 pm

David what weight oil are you using ?

DAVIDLOFLAND · Post by **DAVIDLOFLAND** » Sun May 13, 2012 6:02 pm

Mercruiser 25-40. Expensive, but it took the original long blocks to over 3600 hours. Hard to complain about that.

Mid last summer, when the low pressure issue arose, I did add some Lucas Oil Additiive, which did help some. I will probably add some again, when I change the oil mid-summer.

mitch · Post by **mitch** » Sun May 13, 2012 6:12 pm

troll

prowlersfish · Post by **prowlersfish** » Sun May 13, 2012 6:26 pm

DAVIDLOFLAND wrote:Mercruiser 25-40. Expensive, but it took the original long blocks to over 3600 hours. Hard to complain about that.

Mid last summer, when the low pressure issue arose, I did add some Lucas Oil Additiive, which did help some. I will probably add some again, when I change the oil mid-summer.

that should be fine . I had a 305 that had no oil pressure at idle hot switched to 15w-40 ( from 10-30 ) and got about 10 psi hot at idel . ran it for 5 years and still had pressure at idle l .

mitch · Post by **mitch** » Sun May 13, 2012 6:34 pm

troll

Big D · Post by **Big D** » Sun May 13, 2012 10:51 pm

mitch wrote:Maybe 10 psi at the pump, but zero at the end of the oil line, failure of last bearing.....

Mitch, I'm trying to understand your statement, perhaps you can clarify;
- How would he be reading 10 psi at the pump when the sender is in the main oil gallery?

- Given that the bearings are fed from the main gallery, and that the pump will supply much more oil to the gallery than will be lost through a few high clearances, how would there be a "failure of the last bearing"?

Bearings fail for many reasons, but I haven't heard of one failing because it was last in line. There will be 10 psi at both ends of the gallery, not 10 at one end and "...zero at the end of the oil line..." (hydraulics). Pressure is a function of all the clearances in the circuit, which is last? Correct me if I'm wrong, but if a first or last bearing is worn, it's usually a function of loads, poor maintenance, mechnical, lubrication failure etc. Yes, No?

Dave, not what we were all hoping to hear but you now have your answer, and as Mitch pointed out, it is likely just the mains but while she's out, I'd go the extra step and replace rod and cam bearings; you're already in there. I'd be very careful this season, don't push her. Though you're reading higher pressures, the cause of the low pressure is still there; high clearances, and high loads will kill her faster. High pressure pump or not, those bearings started wearing progressively faster last year, and will continue to do so. If the cure were simply higher pressure pumps, that would be great, but it's not that simple. In some high oil pressure desiel apps, the worry is bearing errosion from high oil pressure.

If your app doesn't currently incorporate an engine oil cooler (like the tranny), I'd stick one in there. Do the same for the other engine.

DAVIDLOFLAND · Post by **DAVIDLOFLAND** » Sun May 13, 2012 10:55 pm

Thanks Big D,

Gonna shop new assemblies, and maybe have them on hand, in case the engine fails before end of season. I intended to do a major repower this coming winter, or next, even before the oil pressure issue.

Big D · Post by **Big D** » Sun May 13, 2012 11:23 pm

Don't know how handy you are, but when you're ready, install new bearings, and put both up for sale. I'm sure there will be others looking for a set up with a counter-rotator. That'll help offset the cost of the repower.