Ok so I have carb motors but I’m running the 2 hose EFI style thermostat housing and a recirc pump. I have high pressure that’s rpm based. I can rev up in neutral and get the pressure to jump to 30+. I decided to try a bypass from plug in from of intake to a T on riser hose. (Gil exhaust). This worked. I’m going to do all 4 to get pressure back to normal.

Now my biggest question is should I need check valves on these bypasses. I did a test run with the first bypass in and things are certainly improved. Didn’t notice anything negative but just curious if these bypasses should have check valves or will it not matter?

https://cimg2.ibsrv.net/gimg/www.off...66dbbadc0.jpeg

The white line is where the bypass hose runs. T on the Gil riser hose. Barb fitting replacing plug in intake

1/2 inch hoses. I’m just curious if I’d need a check valve to keep manifold water from going into engine. But yes the first one is done and everything seemed ok on sea trial.

It’ll be a while before I get it post a pic. The easy numbers to remember were non bypassed 30+ over 5k. Bypassed on one side was less then 20. This was tied to dock in neutral. So the second bypass should relieve enough pressure so it’s back to speed pressure and not rpm based.

These are the Ts I’m gonna go with. I bought Ts and nipples but the kit is too big to look clean so gonna swap to these. Also just a nipple threaded in place of the plug with some 1/2 inch heater hose from auto parts store. Clean set up.

1 Inch x 1 Inch x 1/2 Inch PEX Tee, Brass Construction

let me know how it goes for you also.

oh. Yeah I’ll have mine done in a couple weeks. Doing new fairing as well. I also added the link to my previous post about the Ts I’m swapping too for a cleaner look. Good luck when you get to it. Lol

So does anyone think I’ll need check valves for this?

That’s what I was thinking. I’m sure at times some of the manifold to riser water will go intake but that would just warm up the engine faster. Only having one side done for first test proved very effective. So doing the other side should remedy all pressure issues.

that would work also. My Strainers have a pressure relief port I just want less hoses and rigging in the bilge. This is an easy add without drilling or anything. If I had pressure issues from pickups/speeds I might go that route but this is engine based pressure. Rpm builds pressure not speed

Not always. I can build over 30psi tied to the dock in neutral on throttle only. So mine is in the engine. Likely has to do with me using the newer FI style thermostat housing with no bypass from intake to water pump. Carb motors came with the old 4 hose style.

youre oversimplifying it. We have multiple pressure sources and not going into a closed box. It’s a flow through system and and restriction can raise pressure. I’m not debating how I’m relieving pressure. I know what I’m doing and it works. I was just curious if I would need a check valve to stop water from back flowing into intake. I didn’t think so but was checking to see if someone had a good reason I would need to.

Set up like this.

Genuine Mercury & Mercruiser parts. THERMOSTAT HOUSING(FUEL COOLED SYSTEM) SN 0K147349 & BELOW

The bypasses are working great for those interested. Pressures staying in the mid 20s. Only one side bypassed seems to be plenty.