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Fired The New Motor Tonight (Long)

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Old 04-17-2002, 11:51 AM
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The part number for the 30 psi bypass valve is 25161284. It is installed in the round off center hole. It is much harder to open. The egg-shaped off center hole is the oil from the pump. Since you are using a remote filter with cooler in line, the center hole should not have a valve in it. This is for your return line from the filter and cooler. Mr Gadget's memory is not that bad!

If you are using a Mercury or similar adapter on the block's oil filter pad, then these instructions will work. If you happen to be using a GM or aftermarket blockoff plate on the block's oil filter pad, then you would actually plug the center hole and return the oil to the block through the 3/8 hole located just above the filter pad. This would allow you replace the sharp 90 in the block with a smooth curved line outside the block.

If you have the Mercury adapter like I do, then don't worry about this last little bit of oil pressure optimisation. It's the 90 degree elbows that are the worst. I use the Aeroquip blue lines, FC332-10, 5/8, with brass fittings that are drilled 1/2".

I have installed my oil temperature senders in the 3/8 hole just above the filter pad to measure the temperature returning from the cooler just before it enters the main oil gallery. Funny thing though, in this position I never got a high temperature at WOT. But after returning to idle, my oil pressure would drop greatly. After a few minutes of fast idle, the pressure would come back up. My oil pressure senders are in the remote oil filter adapter, after the filter.

I figure that the oil was just bypassing the filter, cooler and temperature sender and going back to the engine, overheating, and losing viscosity. At high RPM there was still lots of pressure, but most of the oil was taking the easy way back to the engine through the bypass. Back at idle, the hot oil couldn't make any pressure, even though the bypass was now closed and oil was flowing through the remote lines.

I'm not in the water yet this year, so I can't report the results, but not only did I change the oil bypass setup, eliminating three 90s in the block, I removed three brass 90s in the remote lines. Just never thought about them before!

Good luck with your setup and keep us posted.
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Old 04-17-2002, 11:08 PM
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Hi Mr. G., Gotta Hav it, High Priority and tomcat. Thanks for your input.

First off, I think I should be OK with the 24 B1 based on my previous try out of one last fall. I actually like the extra stern lift that it gives on this boat. My 260 porpoises a little with the three blade when trimmed out. The 4 blade eliminated that. I could turn the 24 at 4300 rpm with the old motor so I should be in the ballpark with the extra 100 hp or so from the 502. Time will tell, of course.

I am using the stock Merc remote filter and oil cooler from the 7.4L. The oil comes out of the adapter (which flows out and back in just like a filter on the engine would) through a straight hose to the remote filter pad. The opposite end of the remote pad is where I have the temp sender. It seems to me that monitoring the oil temp as soon as it comes out of the engine would give you the actual reading of the oil in the engine, maybe only a degree or two less due to cooling in the hose. The hot oil then flows through the filter and out through a straight fitting through the hose, to a 45* swivel fitting into the cooler, out another 45* swivel fitting, through the hose with a straight fitting into the center of the of the adapter and back into the engine. The cooler is only 2 1/4" X 4". Probably too small but I will have to try it and see.

I am going to try this setup for reference and see how it works before I change anything. Who knows, it just might be OK. If the oil is getting too hot, the first thing I will try is the 30psi bypass valve in the filter pad and block off the one in the block or maybe put a 30 psi one in there, too. They're only about 4 bucks each. That way I will get more oil through the cooler. If that doesn't work I think the next step will be either a larger cooler or larger lines or both.

I'll keep you posted as I find out.

tomcat, thanks for part # on the 30 psi valve. I went to the Chevy dealer today and the GM Performance book only lists one valve and that is a different #. The one I bought is the same as the one in the book.

See ya, Doug

Last edited by MACDAD260; 04-17-2002 at 11:13 PM.
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Old 04-17-2002, 11:28 PM
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If you just ordered a bypass from Chev it is probably the 11 or 7 psi one. I had to dig up the part number because dealer could not find the 30 psi part number in any of his books or computer search.

The only way the 3/8" cooler lines can be used in any gen v or VI block is with the chev cooler kit. It has a special adapter that goes in the 3/8 hole. If this special adapter is not used oil will not be forced thru the cooler.
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Old 04-17-2002, 11:55 PM
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Hi Turbojack,

The original stock 7.4L has two bypass valves, one in the filter pad and one up in the block above the threaded part that the filter would screw onto. The external cooler line holes in the block are plugged on both engines as these are never used on a marine application. The 502 came without a valve in the filter pad. It has one up in the block like the 7.4L. The engine had been setting around for some time so I don't know if they just aren't used on a 502 or if it was robbed out of the engine. My engine builder didn't seem to think it was needed but I put one in there anyway just so it would be the same as the 7.4L since I am using all of those parts. I was surprised that the Chevy dealer had them in stock. I can't imagine that there would be much of a demand. My good luck I guess.

Thanks, Doug
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