898 cooling questions

[redjmp]

After posting that 1 manifold was hotter than the other, it was suggested that my cooling system was installed improperly.
Originally all I had were the 2 hoses from the t-stat cover running to the bottom of the manifolds. The 4 inlet/outlets in the housing itself were just looped back to each other.

Now I have gone and installed a couple of brass fittings in the risers and ran the hoses from the cover to those.

I ran 2 new hoses from the outlets in the housing to the bottom of the manifolds and looped the 2 inlets together.

Now the risers are stone cold, the manifolds do get hot especially at the bottom but the motor never gets past 120 degrees.

Would it make a difference if I installed 2 more fittings on the manifold and ran return lines to the inlets on the housing?

My merc parts man sugested to do it like I have done but I am not sure.

My clymer book shows 6 lines for this motor but there are less lines on newer motors.
Now these are essentially all the same 305/350 blocks and the risers and manifolds are the same as well( well not really as mine have been replaced with center rise aqua power ones as opposed to the log style rear rise type that came stock) so why were there changes to the design along the way? Theoretically should not all of these configurations work?
I can only assume that the boat ran fine before with all 4 lines from the housing effectively plugged.
But I don't see how it was able to cool anything at all in that state as the t-stat would have blocked all flow going through the cover hoses to the manifold.

Maybe I should run the cover lines back to the manifolds as before and run the new lines from the outlets to the new fittings on the risers?

What do you guys think?
I don't think its running right the way it is now as the t-stat never gets to open.

1st pic is the newone. 2nd is the way it was before.

 

[Don S]

Re: 898 cooling questions

I finally figured this mess out. The way you have it in both of those photos is wrong.
Why you ask? Because you have a very early model thermostat housing for the log style manifolds that had seperate hoses going into and out of the stat housing and manifolds. Like in the first picture (click on it, it's too big to link to.)
The way you have the hoses in your second picture is much better that in your first.

The fist pic is just wrong.
Look at the diagram I posted below, and pay attention to the thermostat housing pictures at the top.

 

[Don S]

Re: 898 cooling questions

Here is a couple of pictures that shows the type system you are trying to get. Note the thermostat housing is different. There is a T in the front of it where your present housing only has a plug. Plus your present housing has 4 other openings that this one doesn't.
You either need to change thermostat housings, or go back to the old style manifolds and risers for your present thermostat housing.

 

[redjmp]

Re: 898 cooling questions

post deleted

 

[redjmp]

Re: 898 cooling questions

Ok I see now...

The 898 system routes water through the engine and then the manifolds before it gets to the thermostat.

Am I correct to think that excess water from the leg flows up unheated through the t-stat housing and out the cover bypassing the t-stat altogether?
This being the reason my risers are now stone cold?

Now I'm pretty sure I could make it work by adding 2 more fittings to the manifolds so it flows just like an 898 does, but is the newer t-stat housing design better?

Wasn't the way it was originally the way to run it so that the manifolds ran the coolest way possible?

Isn't that the objective?

I don't know if I would be better off to spend more cash on adding 2 more fittings, hose and clamps all to make the system run even hotter? ( by dumping the excess leg water to the risers instead of the manifolds) but what do I know hehehe.

 

[Bondo]

Re: 898 cooling questions

Ayuh,... Ya need the T-stat housing that Matches the style of exhaust manifolds ya got....
Change 1, or the Other....

A T-stat housing from about 83 to 90 would be Best...

Oh,... You also should be swappin' the manifold/ riser gaskets when ya change the plumbin' around,...
Some are restricted,+ some are Full flow,+ some don't flow, at All...

 

[redjmp]

Re: 898 cooling questions

Thanks!
After further reading, I see that my 898 has a "Warm Manifold" design that had been converted essentially to a "cold manifold" design.

I also now understand that the warm manifold design keeps the manifolds above 110 degrees to avoid accumulation of condensation.

But why had mine been switched around to the cool layout?

My manifolds have holes at either end for flow through so its not still a question of manifold design is it?

Perhaps its a safety thing with it maybe running too hot in the bilge?

Or maybe it has something to do with what the raw water temp is?

Not sure why there are any Cool Manifold systems if they promote condensation?

And now I am looking for the newer housing but they all have the raw water intake on the wrong side!

 

[redjmp]

Re: 898 cooling questions

OK after some trial and tribulation I have it conquered it without changing either the housing(which is NLA) or the manifolds (which are almost new).

I replaced the riser gaskets with solid ones and ran an intake fitting with drain plugs to the lower rear of the manifolds and an outlet at the top just in front of the riser.

It works great and cost with hose and clamps under $50.