I posted this before just making sure I'm ok. got about 20 25 hours on a rebuilt 502. OP is 40-45 at idle and while running, sometimes running hard at 4600-5000 rpms it drops to 30-35 lbs, goes right back to 40 if I back off throttle. I was told this motor has a high volume oil pump, could that be the reason? It also has crane roller rockers if that matters. Is this anything that I should be concerned about? I realize the OP gauge is not 100% accurate, just being cautious.

other than that, the motor runs flawless.

What type of oil are you running?

 

Check it with a Mechanical gauge

 

You should have 10 psi of oil for every 1k rpm. How big of an oil pan are you running?

 

I'm running a high volume pump in my 500's (now 540's) I beleive the pumps are Mellings 10778"s. At idle I'm at 60-70.....running hard I can bury the needle on the 80 psi gauge. Sounds like yours is the stock pump.

I'm running Valvoline VR1 straight 40W oil in the stock oil pan.

 

Sounds like you are pumping the pan dry and sucking some air. As you slow down , your not pumping as much and giving the oil enough time to run back to the pan. Make sure the oil is full to the line. Low level will only worsten the situation.

 

I agree....not enough oil or pan is dry and to small...Once you have let it idle for about 10-15 seconds and build solid oil pressure it should remain fairly constant.

 

You say you back off the throttle....HOW LONG till the oil pressure comes back up?

What size of oil pan is it!!!!

Did you use the same oil pan as STOCK 502?

Do you have an oil cooler?

IF you are running hard and the oil pressure drops it can be caused by a few different things.

1. Oil does not have enough time to sit it the pan to get rid of the air introduced by windage and splashing around. Pumping foamy oil.

2. Oil is completely being pumped into the motor out of the pan and cavitating the pump. (runs out of oil)

3. Oil is over pressurizing and opening the pressure relief valve causing the drop in pressure.

 

Oil pressure is a combination of bearing clearances and pump capabilities.

Too high of oil pressure is not good but is better than too low.

Too high can mean the oil is not warm enough for the speeds ( RPM's) you are running. Over pressurizing the oil system and possibly causing pressure relief valve to unseat. Or the oil pressure bypass valve in the oil filter to unseat and causing dirty oil to go through engine.

 

Good info Opie! Thanks.

 

Oil pressure is a combination of bearing clearances and pump capabilities.

Too high of oil pressure is not good but is better than too low.

Too high can mean the oil is not warm enough for the speeds ( RPM's) you are running. Over pressurizing the oil system and possibly causing pressure relief valve to unseat. Or the oil pressure bypass valve in the oil filter to unseat and causing dirty oil to go through engine.

All great advice.

My guess is that you do not have enough oil in your crankcase. How many quarts did you put in ?

I bought a large oil pan for my Baja and was told it was 8 quart pan. I filled with 8 quarts and I experienced same problem - oil psi dropped off when running hard. I added 2 more quarts and everything was great.

 

Now I run stock 454 mag mpi's with 40W royal purple. And When I start them and the engines warm up oil pressure is around 40-45 at idle. And around 50psi running hard but after running hard and I come back down to an idle the pressure is around 25psi.

 

Now we are getting into a whole new topic within itself. How much oil to run per oil pan? It is a huge topic with many different opinions. There are guys that run 10 qts in a 14 qt pan, some that run 12, and some that run 14. Some will take into account the oil cooler and the hoses and try to compensate, some do not. Tough topic. :yak:

 

Now we are getting into a whole new topic within itself. How much oil to run per oil pan? It is a huge topic with many different opinions. There are guys that run 10 qts in a 14 qt pan, some that run 12, and some that run 14. Some will take into account the oil cooler and the hoses and try to compensate, some do not. Tough topic. :yak:

You are right but the amount of oil is the assumed source of his problem. I had an oil pick-up tube break off last summer. The engine would start up and build pressure for about 30 seconds...then it would drop to ZERO. The pump could pull the top layer of oil but once oil started filling the top of the motor the lack of a pickup tube wouldn't allow the pump to get the rest of the oil it needed.
BTW: I have the stock 8 qt pans.....takes over 11 qts to fill mine up on the dip stick. Between the oil coolers, remote oil filter mounts/hoses, prelubers/hoses they eat up another 3-3.5 qts per motor.

 

I posted this before just making sure I'm ok. got about 20 25 hours on a rebuilt 502. OP is 40-45 at idle and while running, sometimes running hard at 4600-5000 rpms it drops to 30-35 lbs, goes right back to 40 if I back off throttle. I was told this motor has a high volume oil pump, could that be the reason? It also has crane roller rockers if that matters. Is this anything that I should be concerned about? I realize the OP gauge is not 100% accurate, just being cautious.

other than that, the motor runs flawless.

I can tell you this, just because it's a High Volume pump, dos'nt mean you should have a sacrifice in oil pressure, that's determined by the spring in the pump, A HV pump just has Longer Rotors to flow more gpm than a stock pump, some engines Need the HV pump, depending on many things, large Connecting Rod Side clearances is a big reason, besides certain lifters gobble oil up, besides generally large bearing clearances. so all that being said, it's not because of the kind of pump you have, but could mean the pan needs more capacity, but maybe other reasons too., it could be a faulty pump OR bad installation.
But 1st,, make sure your not Over filled , it's just as bad to overfill, as it is to under-fill, when Overfilled, the oil gets Foamed from being beat by the rotating Assembly. So if your positive it's not overfilled, then try adding a QT, and do the same run as before, and see if it improves, whatever it is, I would'nt feel to good about running at 5000 rpm with only 30-35 psi.
Are you sure the dipstick has the correct oil level markings on it.??? Was it replaced on the rebuild.
If you had this engine built for you, I'd be on the phone with the re-builder, like pronto..and talk with them..

Just curious,, what kind of oil wt are you using and is it synthetic??

 

I agree with Fyre. The only time I had this problem it was due to windage in the pan. Reducing oil level will help but then you will run higher oil temps due to less oil. I would drain the oil, add 6 qts and run it. Assuming the pickup is in place and within 1/2" or the pan you won't suck it dry.

Make sure you don't see this drop too often before you fix it. My end result was mains out and complete rebuilds due to this cavitation of the pump due to foaming. Then I added proper windage trays and larger race pans to solve the problem.

 

Thanks all, it is a stock 502 pan, I changed the oil this spring,3 hrs, I put in 8 qts, manual says 7 for a 502, I used VR1 20/50 I couldnt find 40W VR1, I am using a Pure One filter.

It actually seems to only drop when I am in a little chop, the other day I was in flat water and it was a steady 40-45 at 4500-4700.

I'll check the dipstick tonight,

 

Mine was missing the windage trays. You could smell burning oil from the helm due to it spashing on the underside of the pistons. Any oil smell in yours when running hard?

 

dipstick was reused, I cant remember if the long block I bought came with an oil pan or we re-used my old pan. either way they should both be stock 502 pans

 

with the proper oil cooler the 6qt pan is fine. You just need to make sure it has the proper level that includes all your plumbing/coolers etc as mentioned above.
The stock 502 has a windage tray on it attached to the main cap bolts/studs.
I build a 502 in 96 that's still running with that 6qt pan. I changed to the 8 qt Merc pan when I added the ProCharger which was oil fed, but removed both when I sold the boat, reinstalling the stock 6qt.
And yes the stock 502 does come with a hi volume pump.

 

What happened to your original block? Chances are the replacement block didn't come with a windage tray or the right main cap bolts to mount it. Therefore you would have needed to transfer the main bolts and tray to the new block. That is how mine was minus a windage tray. The guy I bought the boat from blew an engine on my sea trial. Then he put a remanned longblock in it and returned the blown engine as a core (I think). Anyway, I ended up buying the boat without the one windage tray and was getting the same OP drop you describe.

 

Thanks, I'll check with the guy I bought the motor from and the installer today and ask about the windage tray.

I dont remember smelling oil. This motor doesnt burn any oil compared to my old motor. The oil is right at the full line.

I pulled back pretty much as soon as the OP was dropping so I dont think any damage was done.

 

Thanks all, it is a stock 502 pan, I changed the oil this spring,3 hrs, I put in 8 qts, manual says 7 for a 502, I used VR1 20/50 I couldnt find 40W VR1, I am using a Pure One filter.

It actually seems to only drop when I am in a little chop, the other day I was in flat water and it was a steady 40-45 at 4500-4700.

I'll check the dipstick tonight,

I had the same issue as you. went to 8 quarts as you did and it went away. this put it at 1 quart over on the stick.

first verify the gauge with a mechanical gauge

Get a different oil filter. Pure1 is garbage. use Fram HP series or the Wix Racing.

then try pulling one quart out of the motor, and see how pressure is (7 quarts)

then try adding an additional quart and see the pressure (9 quarts)

Lots of extra line, large cooler etc adds to the amount of oil you need total. There is no way that you should need 9 quarts, but for a test it won't hurt anything.

 

Thanks, I'll try all that this weekend.

 

with the proper oil cooler the 6qt pan is fine. You just need to make sure it has the proper level that includes all your plumbing/coolers etc as mentioned above.

I ran a "high performance- not stock" 6 Qt oil pan and had the exact same problem.

Oil starvation when run hard after about 1.5 minutes.

Pressure would drop and fluctuate. Let it sit at idle for a minute and oil pressure would recover.

In my personal experience there is a difference in a 502 and 540 when it comes to windage and oil control issues.

I had a 2 qt oil filter, 2 qt oil cooler, and all the external lines. Still ran out of oil after a hard run.

This info tells me that the 6Qt oil pan is marginal at best for good oil control.

 

going to replace my filter with a Wix or K/N, I read a long article on Valvoline's site, it said the straight weight oils will no longer be made because a multi grade will do the same task. The made a big deal not to call their oil, multi-viscosity oil.

When you say check with a mechanical gauge, how do a do that? screw a gauge into the block or replace my dash gauge with a mechanical one?

It would be pretty difficult to check a gauge on the block when running close to wide open,