This a great thread with a ton of good info. One thing that puzzles me is why the need for large oil lines to the filter block and cooler? The hole passage from the block is small. Currently i'm using the Merc 575 SCI set up on my 871 540's. I am also using the large style HP6 Wix filter. Anybody see any issue with this set up? Also anybody use the Kendall GT motor oil 20-50W?

there is no genuine need. the majority of the time people do it because they look zoomy and because of mythology and folklore. unless you are running extremely long lines the area of your lines need be only that of the largest internal oil galley of the block.

in a nominal set of conditions any good quality motor oil will do the job just fine. when you get into extreme duty like some of the big blower motors on here typical street grade oils might lack some of the additive components required to make them live a long time . like anything else there is no " one size fits all " answer. your oil line , oil, oil filter and everything else will be specific to your motor and what it needs. a box stock 502 mag will run for 20 years with the oil lines it comes with and your 20 =50 kendal but one of smittys monsters will require bigger , more and tougher everything else to live.

I think this has been brought up before but when I sized my lines at -12 vs -10 the main reason was the restriction in the fittings, I tried to keep every fitting's id at a minimum of 1/2", some of the -10 stuff although 1/2 inch or so on the hoses had smaller fittings when it came to 90's /and adapters that were neccesary for clearence. When I prep a block any time I assemble a motor I take a hard look at id of main oil passages too and how they line up with adapters. If I see a oil gallery that can be bored or blended to help with flow I go after it.
Kendall GT used to be considered a good racing oil years ago from what I have been told by the older racers but it was sorta green back then, had a ton of ZDDP, nowadays it isn't anything all too special but I wouldn't be afraid to run it, Smitty

thanks. The 575 SCI lines are only #8 AN. I have 871's but i guess with the big filter and large Canton pan, i've never had an issue with to high oil temps. 212 is about it. granted i don't run hard for very long.

So what if any of these relief valves will I need to change for a 1979 Mark3/4 engine. Not sure which it is. I think its a mark 3 454

Great, Great, Great, Great info here..... this should be a must read everybody......... I have a lowly 7.4L Gen 6 that has been bumped up with a magnum cam and ported oval port heads with big valves and a tune..... I notice that every time I cruise over about 3,500 rpm, the oil pressure will steadily start to drop somewhat and i assume it is from the temp increasing. Normally idle psi is at 40 but hot is 18-20.... Running presure normal cruise is about 50-60 and hot it drops to 40-45......This is acceptable for sure and I am running a Melling HV oil pump. I am thinking about removing the center oil restrictor and hopefully I have a 30LB outer restrictor? I will get a larger (longer) oil cooler installed with an adapter to run -10 or -12 lines. I think this is cheap insurance and a must mod for just about any big block engine....... It is not expensive or complicated to do. I will also install an oil temp gauge and think a water pressure gauge is a good idea as well. I am all about preventive maintenance here after blowing my first rebuild so I want to do everything I can to increase the longevity of my engine...... TBF

I know this posting is from 2005. What is the best artical/thread about this zz502 marine installation. I just bought a boat and it has the zz502 engine and he said its is marinized . just wanting to double check what i can and do upgrades if needed

I'm going to install the freeze plug on the recommendation of this thread but I can't find a 20 mm plug. The closest one is from napa and it is 20.29 mm. Will that work

tmbl52, I have linked my thread which addresses what plug will fit the bypass hole. A 13/16 plug will fit, but you will have to grind or turn down the height to get it to fit flush with the block.

http://www.offshoreonly.com/forums/g...ot-bypass.html

Thanks

Ok so I blocked the outside hole but couldn't get the center one out before it was time to head to the lake. I couldn't get a bolt to work on either bypass so I just popped the outside one out with a screwdriver but the center one is too deep for that. Taking just the one out helped my oil pressure problem out quite a bit, but not enough so I need to get center bypass out. Does anyone have any ideas for getting that one out? I tried different size bolts and lag bolts but nothing would grab a hold. I did not try metric however

I used a starter bolt and tapped it in with a hammer.

Just went through all this stuff, pulled out the valves, changed to a remote filter pad that blocks the relief hole in the pad. Did new thermostatic oil coolers with all -12 lines and fittings. Oil pressure now stays 60psi at idle and 80psi at speed regardless of temp, which with the new coolers does not go over 220. Definitely a big difference.

Never mind - did not see that you blocked the outside bypass. Center bypass just routes the oil through some extra passages for the external cooler. May or may not help your pressure to remove this.

feel like putting together a walk through for us non mechanical types?

Out of curiosity, what was your oil pressure before these modifications?

Bump as this seems relevant here lately.

Just clarifying the oil route so I don't get anything crossed up. The oil leaves the block adaptor from the offset nipple, to the remote oil filter, to the oil cooler, and then back to the center port on the block adaptor, correct?

Yes.

I currently have been using a moroso sandwich filter block adapter on a Merlin block however the outer o ring lands just barely on the edge of the block filter pad as this block pad is smaller than the ones on the GM blocks. I am concerned about it leaking a little there. I like the simple pluming with this setup and can just reach the filter to change it. Does anyone make a sandwich adapter with the double o ring seal for the Merlin blocks or do I need to either fabricate a special gasket for the adapter to block seal or go to the double o ring block adapter and set up a remote filter?

If it has two bolts that hold the block adapter to the filter pad (Mark iv) I have everything you need to mount the filter off the back of the port head with lines. Pm me if interested. If not interested in what I have everyone and there brother makes block adapters that will work.

It is just visible in this picture where the o ring is right at the edge of the block filter pad.

Just finding this thread. I have a pair of 502/502 crate engines that have spent their life in a boat (not mine).

I recently freshened one up that had been marinized before in the cam and valve train area but not sure in the block. Had a marine builder rebuild the short block and we did not check these by-passes. I do have higher than expected oil temp for a 525HP engine with top of the line remote filters and -10 lines. I see 200-210 at easy cruise, and 250 if I lean on it very long.

The second of the 2 is in my garage for a build. I just went out and removed both bypasses and suspect they are both still in the block I am running.

I'll be anxious to see what it looks like when I get it out this winter. Its run fine so far this summer, so it will probably get a few more hours on it as is.

Great thread showing what OSO should be!

I pretty much followed this thread as gospel when I was plumbing my oil system.

Having the bypasses in there isn't a big deal, but do you have the right bypass valves is the important question, and there's no way of telling just by looking at them. From what I understand if you have the 15# valve in there with a remote filter it's only a matter of hours before the bearings are toast so if it's lived this long you may be ok. I don't think the one under the nipple is a big deal until you start getting well above 600hp. -10 lines may still be too small and giving you higher temps. Have a look at this:
http://www.offshoreonly.com/forums/g...il-temp-7.html

Fwiw, I was able to get to my bypass valves with the motor still in the boat. It wasn't fun, but it is doable.

A great thread on oil hardware. Does anyone know if the 500 EFI oil cooling system has larger lines/cooler and would be a reasonable solution if a nice used one is located? Going on a 502 Mag with Whipplecharger.

When i rebuilt a 500 efi 2 years ago for a friend the oil lines were decent compared to the tiny holes in the gen 6 502 mag mpi 415 hp stuff. Keep in mind the problem with 502mpis and these tiny lines becomes s serious issue when guys open up rod and main clearances and install a high volume pump, THEN they become a huge restriction and block bypasses open and regulator bypass in pump is probably buzzing its ass off trying to let oil that cant flow relieve the outlet pressure thats backing up!!

Ttt. 😎

........it has 11lb bypass relief valves. If your motor has unknown origin,who knows what it could have. Buy a new 30lb bypass relief valve for the outside(the one near edge of block casting for filter adapter) or plug it off,they are available at your local chevy dealer part #25013759,they are under 5$. The middle valve directs oil to the cooler fittings...............

Where exactly are the above valves (on the engine) as described in the OP's original post?

They are on the block under the block adapter,the outside valve in the photo has been removed and pluged up

https://cimg0.ibsrv.net/gimg/www.off...b002b9106.jpeg

Thanks I'll have to check into the location of the block adapter. I'm guessing this is where the oil filter would be in an automotive application, bottom side?

I have low oil pressure on a OE 416 hr. '96 7.4 lx mpi. Aside from a bad dash mount oil pressure gauge I don't see why the pressure would be low. I'm hoping switching the valve would help with the pressure issue.

A 11 lb autiomotive valve can only open and allow unfiltered, uncooled oil to bypass the cooler and filter resulting in engine damage if its original with standard volume oil pump, unless bypass is hung open, i doubt its your problem though. Im of the understanding mercruiser used the stiffer bypass valves but not 100% sure. The lines, cooler and bypass were sized appropriately from factory for stock clearances and standard oil pump and usually work for hundreds of hours. Now, if someone put a high volume oil pump in, then it could be bypassing the cooler and filter, smitty

Gotcha, I'll check with another oil pressure gauge first as I'm lost as to what else could cause the low pressure, aside from what you mentioned.

Back to the top. Great thread! This saved me from going from a bad situation (not of my doing) to a much worse one. I remember reading this back when it was first posted and decided go over it again recently. My engine started life as an HP500 and I see it still has the bypass valve on the outer side of the oil filter pad. Being I'm now going with a Melling 10778 I will remove and block with a Melling 13/16 plug and go with a larger oil cooler as well as a high capacity filter pad, lines and filter mount from Hardin Marine thanks to the information found in this thread. One more question though, being I have a choice between an HP4 or HP6 style oil filter, which would be the better option for a blown 509 making 855hp. Sincere thank you to Articfriends and all who contributed here.

210-220°f is optimal...so it has enough thermal capacity to cool the engines parts...mainly the springs.

Standard HP4 is what I would use. We ran the HP6 on the race boat, but for a recreation boat I would just run the HP4. They are readily available anywhere. You never know when you might need to change the oil. Crack in the oil cooler, stuck injector, or bowl seat not shutting off.

Thank you Rookie. Much appreciated.

Don't forget you can run 2x oil filters in parallel. I'm not a fan of the 62 micron ultra flow racing filters. Maybe as a first state, but we don't tear down our engines every few runs.

Lots of good filtration options.

Having a personal experiemce of spinning a main bearing from oil bypass...I don't like it at all. Bypass to oilpan ok of course...but not bypass filtration.

Check out David Vizards newer vids on setting up the oil pump and cleanking up the oil flow path. Worth the watch..and would help you setup your new oil pump.

What would be the best option for a high flow/good filtration Hp4 style filter? I would imagine, like everything else, there is a reasonable compromise?

Just to clarify as I saw some conflicting information in this long thread.

The 30psi bypass valve is part# 25161284.
The 11psi bypass valve is part# 25013759