Hello SB,

Yes, before registering to this forum that's exactly what I did over the course of the summer, was to search the site for boaters with crossover experience.
Some people had good results, while many others experienced the milkshake issue due to not having a bypass and/or pressure relief valve installed. (separate issue altogether)

There was one individual who pretty much described his lack of heating issue to be the same as mine. However, one day, he decided to remove his thermostat and reinstall it exactly the same, and for some unknown reason his temperature issue went away. He couldn't explain it, but the problem was resolved and he was able to maintain full operating temperature. In his case, regardless of what the issue was (Sticking thermostat, etc.) it sounds like a crossover setup can work properly. So, not all hope is lost.

One individual drilled additional holes into his thermostat and that apparently solved the lack of heating issue. Unless there's an anomaly that I'm unable to comprehend, that just make no sense to me. More holes = more cold water flowing through the block. How does that result in increased temps?

Then of course there's the option of replacing the crossover with a circulating pump. That will be my final option if I can't figure this out. I'm sure that most would just resort to doing this and be done with it. However, I'd like to understand what exactly is responsible for this issue.

Thank you all for your input.

Blair

Right in the intake manifold, about 2" to the left of the T-housing.

Essentially, it's the same as drilling a hole in the thermostat to allow circulation, but by installing the Y at the rear of the intake, you promote circulation from front to back, and of course the volume of water circulating through the block is governed by the size of valve you installed? In your case, I assume that tweaking of the valve is what influenced your overall temperature. Did you still run a thermostat as a contingency for overheating?

Correct. For people using t-stats, that's the beauty of the Merc 4 hose (total) t-stat housing. Recirculates a lot of the warm water back to recirculating pump when t-stat is closed. When t-stat opens it does so thru another (the upper) chamber and out the exhaust. The t-stat operates more smoothly this way to vs opening and closing a schitload of times per minute.

What you described is what I've been speculating to be the case. Just to confirm, you're saying that hot water from the block is exiting from one of the inlet ports and back into the crossover, then out the bypass. Correct?

How did you verify that?

I was thinking of replacing the rad hoses that connect to and from the crossover and to the bypass with transparent/clear rad hose. That would enable me to see the directional flow of water. If there's more volume entering one side of the block than the other, that could be creating a circulation effect, and as the hot water leaves the block it gets pushed out the bypass.

You have an IR Gun, check each leg of the cross over to see if you are experiencing unbalanced flow. I have the same setup and it works perfect, although I added a -10 line from the back of the intake to the front intake cross over to bleed off any steam and to insure good water flow to the heads. I have checked my temps with a good IR gun and my temps are within 1-2 degrees everywhere. What is the water temp you are running in? I was out last weekend in 55* water and idling down the river, I barely got to 115*. Once I got to the lake and pushed it hard it warmed right up. Water temp was 155* and oil temp was 250*. Yes I know my oil cooler is a little small.