502 losing oil pressure
 

Got a 502 that seems to be running well but is losing oil pressure. At start up it has 40 psi. Then after about a minute 20 psi. Idle in gear dropping to nothing at all changed the sender and it got worse. No noises from the motor though.

Any ideas???

What kind of oil and how many hours on the oil?

I believe the oil is 20w 50. There is about a half hour on the oil.

I have same motor and fought same problem all season. However my temp was rising as well....

Did you get it straightened out?

No. Without writing you a book, I changed oil 3x. Tried straight 50 w/no change. Back flushed oil coolers which seemed to temporarily work, then removed cooler and inspected, replaced, still same deal. 340 hours on motor. Other motor, runs perfect. Chased it all year and no fix yet. Pulling motors and repower this winter... Sorry man

Rule of Thumb is 10 psi per 1,000 rpm,is this since You changed the oil?did You try a manual gauge yet?If You have a Fram or AC filter that could be the problem,first I would change the oil filter then screw in a manual gauge and see where Your at,The oil would take more than a minute to heat up and lose viscosity,another reason could be if You are getting fuel in the oil,You can tell by smelling it or if the oil level is rising.

It has a mercruiser hi performance long filter on it. How could you get fuel in the oil?

Yes, i agree, it is not heating up enough to thin out. I am hoping that the gauge is bad.

Cut open the oil filter and check it out. Also try a mechanical oil pressure gauge.

cut oil filter open .... first
Mechanical gauge....second
do you have oil temp gauge? that tells everything, if temps are getting hot its usually not a good thing (bearing failure)

then check sender after mech gauge test good...

I don't agree with 10PSI per 1000 rpm, I like 60-80 when over 3000 rpm, I run 75 running hot, 30-40 at idle hot... depends on clearances but I have had issues with low oil pressures on boat engines that run oil thru coolers and such, also make sure you have a 30lb bypass or none at all, and always run hp series filter with no bypass...

good luck!

I had the same problem and it was spun crank bearing. Motor ran fine believe it or not and it finally blew after a complete summer of running it. The temp ran kinda hot a little over 200 °. I would get it checked out.

I think I figured it out. I now have 45-50 psi at 900-1000 rpm idle. And yes, it was something really really stupid. I don't think I can elaborate further. It is just plain embarrassing!!!! :fear:

On a motor with clearances set right ,10# per thousand is what gm used to say (bbc) .That being said ,I don't want to idle under 20#'s and the way pumps work , the pressure will rise faster than 10#'s per 1000 throttling up, until you reach the pump blow off pressure. Usually 60 + #'s with the blue spring. Running too much pressure cost power and wears pump / distributor gears faster than necessary.

Shim pump for more pressure, that was advice years ago of Gellner..... hes not new to boat engines... I never wore anything out doing this, ...

You expect to get off that easy around here?? spill it!!

Enquiring minds want to know. You have to tell us. Believe me, no one on here will judge.

You could save a life with your information & think of the children my good man, think of the children!

I have only 15 - 20 psi at idle (750), maybe I have your problem also? Please elaborate, or at least PM.

Come on - spill it !! :whistle:

Trust me no one has this problem

Gee thanks....now I feel even worse!!! :whistle:

Ok ok ok......this is the dumbest thing I have done in a while. I trusted the word of someone else instead of following up on my own, like it would have been so hard to just look at the dipstick.

Yeah, that's right, I just plain trusted someone else that there was oil in the motor, checked it and it was 4 1/2 quarts from full....:eekdrop:

Ugh!!!!!

Holy Yit!!

That will do it...bummer. At least you know whats up now. Hopefully it wasn't run too long that low, thats a lot of oil!

It held pressure I'm sure it's fine. If it was run offshore at 5500 for 45 min yeah it would be bad but in a small single run on the bay I'm pretty sure enough oil stayed in the pan to keep the pick up covered.

my guess is you are not the first guy to run an engine low on oil,nor will you be the last one.it sounds like you got lucky and did not tear anything up.:party-smiley-048:

Not trying to bust balls, but where did the oil go? 4.5 quarts low? How did that happen?

Many years ago, I had a 1978 F250 work truck. It had a 400 Ford engine. My mom called me one evening, and said she has a flat tire, and she was at the shopping mall about 20 miles away. It was getting late, and she was all alone in a dark parking lot. So I hopped in the old work truck with my floor jack and headed to get her, trying to hurry because that area wasn't the greatest. So I get on the hwy, and all of a sudden, my lifters are clattering quite loudly. I carried on, zipping down the hwy. I got off at the exit for the mall, and sitting at a red light, I saw the oil psi gauge going from 30-0psi, back to 30, etc. Pulled in the nearest gas station, and figured id check the oil. Pulled the dipstick and fukin thing coulda melted solder. WOW that's hot I thought. Nothing registered on the dipstick, so I went in and bought 2 quarts, put them in, rechecked. SOB, still nothing. Went back in, bought 3 more qts. it took all 3 and still showed a qt low. At that point, I had to get moving. Fired it back up, lifters continued to rattle for 4-5 seconds, and back to quiet as normal. After that, drove the truck 2 more years and sold it still running fine. Basically, drove 15+ miles with probably 1qt of oil in the thing!

Must have been 1qt of Amsoil Dominator ! :party-smiley-004:

The person who filled it seemed to think that was enough I guess, or they were distracted or something. They told me it was full. And it was far from it.