Mercruiser 228 Thermostat plate/gaskets.

[mogfisher]

Hey folks,

So I'm putting a thermostat in as PM and the local merc dealer said that all the current literature show the gasket with the cut out (reference picture below). My boat had a metal plate and two gaskets without the cut out. The sleeve is brass and has no cut out in it. He did sell me a gasket like the one I had but he only had one. Seems like it should seal fine with one cut and one not but the question is, what is this? Which way do I assemble it? I'm just hoping that someone can shed some light on what this is because I'd really like to know. Clearly this is done for a reason. What is it?

 

[alldodge]

My guess is you need to use the solid one as in this pic


Reason being is because old one did not use one with a slot cutout. The installation sequence is here

 

[mogfisher]

Thats the thing. There IS a slot top and bottom. In the diagram that the dealer eventually found, it showed the block off plate with a gasket on each side. Looked just like that diagram but it showed the plate and 2 gaskets. It's odd. I mostly just want to know what the reason would be to block off this opening.

 

[Pete104]

This was the first attempt for center rise manifolds. And thanks to Mother Mercury, if you can't find it online you better know someone who has paper books.

The flow for the hsg you have gets water to risers & manifolds first as most do but yours is older than any diagram anybody find. The plate is there for water to flow OVER the top of the thermostat while the T-fitting with the checks are keeping exhaust from entering the cooling water. The plate is a block off, a plain old gasket wouldn't cut it!

My Dads boat is a 1983 with 260 hp and it never had this hsg.

 

[alldodge]

Going to center risers does change things with flow. As with another thread, it will depend on keeping warm manifolds or cold

 

[mogfisher]

So it looks like this plate keeps water from flowing past the thermostat unless its open? Without the plate, that hole bypasses the thermostat and allows water to hit the risers? Am I reading this correctly? Thanks for all the help, guys. This is great.

 

[alldodge]

Yes, your correct

 

[mogfisher]

And that is a good thing? Necessary? Why would we not want water on the risers constantly?

 

[alldodge]

Yes, you want water going to the risers all the time the motor is running. The gasket if covering the opening, is only restricting the water flow, it isn't cutting it off (no sealing surface on the other side). So the water has a harder time going around the gasket, and this can help make sure the block is full of water and there are no air bubbles. Removing that part of the gasket will allow more water to flow, and also allow the block to get a bit more cold water, which will increase the warm up time a bit.

Other thermostat housings have fixed smaller holes to restrict the water flow during warm up. They all work, and since the closed off one is harder to find, it could be Merc might have changed to keep it open more so.

I'm just making some assumptions based on my interpretation of what I'm seeing

 

[mogfisher]

I appreciate all the info. I think I have an idea of whats going on now. I see the point about warm up time. Upon looking further, I think the risers do get water always and this is not interfering with that. I think this has to do with the water to the manifolds themselves.

The scoop on this motor is that the boat was given to me and the boat itself is rotten wet bark mulch. I took it for the nice roller galvanized trailer. I'm trying to asses the viability of this motor to see if it is any good. I drained 2 gallons of water from the crank case. The motor was winterized, and the water was perfectly clear and I know the motor was not started with the water in it. My thought is that the boat filled up (uncovered) and the water went in the dipstick tube. It was last started 2 years ago with no water in it and then winterized. I have a total of 15 minutes of run time on it so far and it seems OK. Perhaps a bit noisy but there was still a fair amount of water in the oil. Now that I have the thermostat put together I'll be starting it on its second oil change. I think after this one I'll pull the plugs and check their condition and do a compression test. There was good oil pressure when I ran it last which is a good sign the bearings are OK. If the motor is good, I think I'll pull it, slap a transom floor and stringers in it and go boating!