Bypass Valve
 

Hello all. I have a ZZ502/502 crate motor. I installed an oil temp guage this summer and found that oil temps are way too high. I've tried a larger oil cooler. After trying that, along with a bunch of other stuff, nothing seems to help much. So through the process of elimination, along with research and asking lots of questions, I've come to the conclusion that the 11 lb. relief valve in the block needs to be changed.

I've been told that there are two bypass, or relief valves in the oil filter location {on the block}. My question is, do both of those valves get changed, or just one of them. If just one, which gets changed, the center valve, or the one on the side of the pad.

Thanks in advance.

Re: Bypass Valve
 

Been a while since I did mine, but here's more info...

Excerpt from Speed Reading written by Wade Hajek of GM Performance Parts

Gen V and Gen VI big-block crate engines come with two oil pressure bypass valves installed in the engine blocks. Both of these valves are rated at 11 psi pressure differential. One valve is for the oil filter and the other is for the production oil cooler. If you install an aftermarket oil cooler or remote oil filter that attaches to the oil filter pad on the engine block, you should be aware that you need to change the oil filter bypass valve in the engine block. The aftermarket oil lines add resistance which will cause the bypass valve to bypass the aftermarket oil cooler and/or oil filter all the time. Obviously, if the cooler and filter are bypassed the oil will be dirty and hot. Your engine could run hotter and could be damaged by dirt in the oil. If you choose to use an aftermarket cooler or remote oil filter that attaches to the pad, you should change the bypass valve to one with a higher differential pressure rating.
A good choice would be GM# 25161284 which is rated at 30 psi. Remove the valve that is closest to the crankshaft and replace it with the new valve. Press the new valve into the engine block and stake it in three places. You should note that the bypass valves don't need to be changed if you use a production oil cooler which uses the production holes in the engine block and you don't use a remote oil filter. Also, if you use an adapter that just angles the filter for clearance you don't need to change the bypass valves.

Re: Bypass Valve
 

So don't change the one in the center, just the one that is off to the side?? I ask because I was told that I needed two valves.

Re: Bypass Valve
 

My Gen V 502 only had the valve in the off center location. None in the center.

Re: Bypass Valve
 

Plug the oil cooler ports on the block. Unless you have the special GM adapter that goes in there you will be bypassing your cooler.

Install 30psi bypass on side one. You will not need any in the middle if you use a oil filter adapter to plumb out of.

Re: Bypass Valve
 

Thanks for the responses.

The way I read the GM text that Cignificant posted, there's a valve in the side of the oil filter location. And the 2nd valve must be located in one of the two ports that {I believe} are just in front of the oil pad. There are no oil lines comming from those ports. They are plugged.

We took a Merc 7.4 out of the boat and dropped in the ZZ502. All the marine bolt ons were taken off the 7.4 and put on the ZZ, including the remote filter pad. But the 11 lb. bypass valve in the block/oil filter location was not changed. I'm pretty sure that's the problem.

Thanks again for the information.

Bill

Re: Bypass Valve
 

If you look at oil filter pad on block you will have hole in middle, an oblong hole where oil comes from the oil pump & another hole (round) close to the side. That is the one that needs to be pluggd or the 30lbs bypass installed in. I think the center one is only needed if you are using the cooler holes on the side of the block

Re: Bypass Valve
 

If you remove the center valve the oil can return directly back to the engine. With the center valve installed the oil has to go through the passages to where the production cooler would be if one was installed. Removing the center valve removes an additional restriction in the system which will improve oil flow to the remote filter and cooler by a slight amount. In this case every little bit helps. I went through all of this myself when I swapped a 7.4 for a 502. I ended up with a 3" x 12" cooler and increased the oil line sizes to 10AN. I would recommend an even larger cooler if you have a ZZ502. More horsepower makes more heat. Good luck.

Re: Bypass Valve
 

MACDAD, I think you and I have kicked the oil cooler thing around before. How are your oil temps with the 3 x 12? I tried a 454 mag cooler, no good. I then went to a Hardin Marine 3 x 22 cooler with a tstat. It cools engine oil and power steering. Actually, about 3 x 15 or so is dedicated to the engine oil. It's supposed to be good up to 700 hp. I fugured with my hp at around 500, the Hardin would solve my problem. It's better than the mag cooler, but still not good enough. Process of elimination tells me it's likely the bypass in the block causing the oil temp problem. BTW, I think you mentioned before that the tstat in the oil cooler didn't seem to do much good. After taking a look at mine, I agree. I don't see where it would be of much use. Pretty poor design/fit. Lets lots of oil through open or closed.

Ok, leave the center hole empty, and put the 30 psi valve in the side hole.

I have a pic of what you guys are describing. The pic is on page 10 of Dennis Moore's book; BB Chevy Marine performance. Text under the pic notes the location of the valve.

I'll let you know how things go after valve replacement. Probably a week or two.

Thanks again!

Re: Bypass Valve
 

Just remember that the oil enters the filter on the outside and re enters the block up the center so if the filter was pluged it would re enter through the offset port,therefor it is the bypass port.With the added restiction of the remote filter/cooler this bypass valve needs to be a greater pressure.The bypass in the center is to direct oil over to the cooler port on the block,out to the cooler then back into the block above the valve.Since your ports are plugged the valve is in bypass mode(open) all the time so you might as well turf it.With the stock cooler/fiter being on the same circuit I think there is a fair amount of bypass at start up due to cold thick oil.I would like to try running the filter on the block and using the stock cooler line ports on the block.This would eliminate a lot of external plumbing.You could run a selenoid to stop the flow of oil to the cooler to aid warm up.Your filter would not go into bypass as easy because the oil would be hot at the filter and non restricted by the cooler.Once in the cooler circuit if its getting too thick it would just bypass the cooler only.The stock GM system is excelent as it separates the cooler and filter bypass circuits.The only thing that would improove it is larger cooler ports in the block,but if you increased the cooler capacity knowing only a percentage of the oil is going to the cooler it should still work.The stock marine setup realy is a downgrade on the stock setup.Some times you can't outsmart the general.I have a modified zz 502 that is plumbed in the original remote filter cooler fashion with the heavier bypass and I had to inrease my cooler size due to oil temp problems(270 plus).I have an Edie 3"x18" combo cooler and I never hit more than 240 with 30 wt.dino oil.The problem is it takes a long time to warm up the oil,and if I don't run it hard enough I wont hit 212.Even with the stock undersized cooler I was suprised how long it took for the oil to get warm.I am checking the temps at the filter pad so the oil going into the block will be cooler.The setup works OK if you warm it up slowly(get it on plane but don't bag on it).I would be carfull withh that zz motor if your not using dry exhaust as they suffer from bad reversion if precautions are not taken.I can expand on that if you like.

Re: Bypass Valve
 

To answer your question I would change the bypass and your problem should be solved.I had the same problem plumbing a truck with a remote pad kit.The oil would not go to the cooler due to the bypass valve.The cooler wouldn't even get warm.I ended up using the block ports to get it to flow to the cooler.Extreme heat can also be caused by detonation and other nasty things but I think your problem is the 5$ valve that requires engine removal to install.You should have got a memo when you got this motor from GM.

Re: Bypass Valve
 

I have been dealing with this issue, Changed the bypass in the block, put everything back together then found same problem. Turns out that some MERC screw on adapters for oil coolers also have a bypass built in. If you have higher than stock oil pressure this thing opens and stays open. Had to take engine back out because Cast Oil pan didn't allow removal of adapter. Decided to plug all bypass valves, block and adapter, put small mech oil guages before and after filter to watch filter condition. This gave dramatic reduction in oil temps. I also have the 3x22 combo oil cooler with 580HP it is apparently not enough for extended hard running. Am looking for economical upgrade for this piece.

Mark

Re: Bypass Valve
 

As Mark said that is a sure way to force oil through the cooler and filter by pluging the bypass.Just make sure you monitor pressure on both sides of the filter and use a high pressure filter.

Re: Bypass Valve
 

I beleive the Adapters with built in bypass were fitted to gen 4 motors. So this is something to watch out for if you install Gen5 or 6.

Mark

Re: Bypass Valve
 

HARRISON, Great explanation. I was surprised at how many engine guys are not aware of this problem. A respected local guru offered this; usually marine mechs do a rebuild with an existing damaged marine BB like a 454 or 502. Or if they start from scratch to build a monster they'll buy a new Merlin or Bow Tie block, and go from there. So not many builders run in to the bypass valve situation. Makes sense, but it still sucks.

About the only thing I haven't done yet in relation to the oil temp dilemma is change the impeller in the sea pump. Never a problem with engine water temp, so I assume the impeller is still good, and is therefore pushing enough water through the oil cooler. But to be safe/sure, the impeller will get changed when the valve gets changed.

I'm aware of possible reversion issues with the ZZ cam. To help avoid reversion I replaced the stock Merc exhaust system with Revolution Marine exhaust, and added a 3 inch spacer between the manifolds and risers. With the Rev system as is, the pitch from the riser to the tips is pretty steep. I would guess about 30 degrees. Also, the Rev's have a small "reversion dam" built into the risers just after where the water dumps. Plus, I try and remember to keep the idle up to or over 800 rpm's. Lower when shifting. And I rev the ZZ up a few times before shutting down after low idle times and or docking. If you can offer more on the subject I'm all ears!

Thanks for the input!

Re: Bypass Valve
 

Mark, I've read/heard that the Gen IV had a bypass in the oil pad adapter that screws on to the block. My boat is a 1995 and I'm sure the 7.4 that was taken out was the original. So, I think that would make it a Gen V. But thanks, I'll be sure and check for a valve in the screw on, and up at the filter.

Oil pressure at idle is about 45. OP at WOT is about 55 or so. I would consider that to be good oil pressure, but not high. What do you guys think?

Bill

Re: Bypass Valve
 

This has had me wondering about a friend of mines problem.
He just purchased a boat that needed to have one motor rebuilt with a new block.
These are HP500EFIs and when starting out and the motors are cool he has 65 lbs in both motors. When the temp comes up stabilizes the original motor drops to 45 lbs at cruise and the new one drops to 25 lbs. The 25 lbs is abnormal and I’m wondering if they could have made an error when or if they installed the bypass.
I’m not familiar with the 500EFIs oil thermostat or if they even have one but what would be the symptoms be if no bypasses (or maybe the wrong one) were installed in the new block?

Dave

Re: Bypass Valve
 

I can't answer that question, however, rebuilt blocks often are baked with the bypass valve in place, this can dramaticly weaken them. Do you have oil temp info?

Mark

Re: Bypass Valve
 

Heat, I installed my oil temp gauge this spring. I went through last season without a guage, and had a stock 7.4 oil cooler on the ZZ502. After a hard run oil pressure back at idle would sometimes drop to +,-20 lbs. which I've heard is not uncommon. But I'm sure the low oil pressure at idle was due to the oil being too hot. After installing the oil temp gauge and now being able to monitor the oil temp, I back off the throttle when the oil temp gets to 260* or so. And oil pressure at idle is now around 45 lbs. I use synthetic oil. I think the synthetic being better at high temps is what has saved the ZZ from damage. At least any known damage.

Most, or at least allot of people don't have oil temp gauges in their boats. Might be that some would be surprised at their oil temps if they did.

I had a guy tell me "the oil temp gauge is the best $ you will spend on your boat". I believe he was right.

Re: Bypass Valve
 

Many Boat and Harley owners would be suprised by their oil temps. Hope you have looked at M-1 20w50 thread and all the great oil info by Hydrocruiser.

Mark

Re: Bypass Valve
 

mhawkins48,
the block was a new block and they come bare (no valves).
Good point though.
KidNova,
the pressure drops to 25 and 45 on each motor at cruise speeds of 3500-4000 rpm once temps come up.
Thanks,
Dave

Re: Bypass Valve
 

I lurk on OSO often and have been watching that thread. Very interesting to say the least.

My Harley days are over. "back in the day" mine had fresh oil all the time. Just kept on filling the crank case as they leaked it out ;o).

On a more serious note, those back cylinders had to take a beat'n from the heat.

Re: Bypass Valve
 

Dave, maybe you could suggest to your bud that he install oil temp gauges. They are cheap insurance.

Bill

Re: Bypass Valve
 

Kidnova, My oil temp with the 3"x12" cooler has not gone above 240*. Most of the time it is about 220* at a 3600 rpm cruise. Not bad. I might pull it back out next winter and replace the only 2 90* fittings with sweep 90's just to see if it unrestricts the flow a little more. I am glad I went with the 10AN lines and fittings. I think that helped, too. Good luck.

Here is another question for a Merc Engineer type. We are always told to plumb an oil filter/cooler system with large (at least 10AN) lines and to avoid any 90* fittings. How does the oil cooler on a HP525 and HP575 do it's job when they are plumbed with only 8AN line and 4 90* fittings? I can't figure that one out but, it obviously works.

Re: Bypass Valve
 

Before I changed from the stock cooler to the eddie marine 3" with thermostat I had problem of oil pressure dropping & dropping until I slowed down. Once I put bigger cooler on pressure never goes below 60 now.

Re: Bypass Valve
 

Been serching for cooler to meet my needs and fit availiable space and found this site
http://i-netmarine.com/oil_coolers/s...il_coolers.htm

Made by SeaKamp they will build custom sizes also.

I also found that Hardin says that chrone finished coolers are up to 40% less efficient than painted!! :stupid: Could be big part of my problem.

Mark

Re: Bypass Valve
 

Interesting, you can get the length and diameter you want. But you'd have to run a separate power steering cooler. Wonder if SeaKamp would incoropate one into an oil cooler?

I read about the chrome coolers being less efficient before buying the Hardin. I ended up painting mine purple...matches the graffics on the boat.

Re: Bypass Valve
 

Kidnova,

I wish I had known that before buying the Eddie Marine 3x22 combo unit. It would probably be plenty for less than 500HP they claim up to 600 I think. Having done everything else to ensure good water and oil flow, I have decided that this piece is not enough for Texas temps, with 580HP.

I tried to find SeaKamp on the web to see if they build combo. But thinking further I have decided to run separate steering cooler. That will allow me to run bigger oil cooler where the present one is. Steering coolers are so small they can fit just about anywhere. More HP inevitably calls for more cooling/air/fuel and stronger everything else.

Mark