Plug filter bypass?
 

Everyone agree? Should I remove the filter bypass in the remote adaptor (Mark 4, 7.4) and plug it? Nows the time.

For sure !!

What he said

But, if for some reason your filter becomes plugged, motor will not get any oil. And while on this subject, will a filter alone flow enough cold oil until oil is warmed up? I gotta believe that GM and Merc have alot more testing involved and at stake on this item.
enlighten me.

I am running mine just the way it was from Merc. My crazy theory is that Merc knew what they were doing and a good flowing 10w40 oil will easily make it through the filter and cooler with minimal pressure drop if the lines are sized properly. Most boat guys change their oil and filter long before it is plugged with dirt. If you plan on running straight 50 wt. it may be a good idea to plug the bypass.

US1
If the oil bypass pressure is reached the engine will still get oil, but the filter and oil cooler will be bypassed. The bypass is to protect you from blowing the filter if it gets plugged. I believe it is set at around 15 PSI and from my hydraulics engineering days I am here to tell you that 15 PSI would be a pretty dirty filter and/or way to many 90 degree fittings. Bottom line is I really don't think you will ever notice a difference either way. Just my 02.

Not sure I am the one to enlighten you as you have a very good point. GM and Merc have to worry about idiots tha refuse to warm up there motors and warranty though. I have been running plugged by-pass for many years. YOU MUST GET SOME HEAT in the oil before runniing hard if you plug the by-pass. You should anyway! I have never had an oil related problem. I like ALL my oil filtered. There are others on the board with way more expertise than I have but that is just my opinion. :)

What would you gain by doing this?

Heres a quote form Merc's Manual 90-14499-1 887. Page 3B-68
"IMPORTANT. Production-performance engines do not use an oil filter by-pass valve. On these engines, by-pass valve is removed from the adaptor and oil by-pass hole is welded shut. Do not install an adaptor with a by-pass valve incorporated as inadequate oil filtration will result."

No don't plug it...
 

There is a big misconception about the oil filter bypass. Most people believe that it opens at 15 pounds of pressure. It doesn't, it opens when the pressure difference is 15 pounds. In other words, when there is 15 pounds of restriction in the filter.

If the engine has 50 pounds of oil pressure going into the filter, the bypass wouldn't open until the pressure coming out of the filter dropped to less than 35 pounds. The bypass seldom opens and bypasses the filter.

I wouldn't trust Mercruisers expertise on this matter, every Merc HP engine I have ever worked on has the oil filter bypass, I don't care what the manual says! (plenty of errors in those manuals!)

Leave it in there!
Sincerely
Dennis Moore

I hear ya, but, with the thermostat, oil cooler, hoses to the remote filter, and the filter, I wouldnt be surprised if there is a 15lb drop through all that stuff, especially when the oil is cold. Lets rephrase that question. Assuming I change oil filters frequently, which I do, would there be any downside to plugging the relief valve. Especially considering the pump has its own relief valve.