888 running cold

[atuomi]

I recently bought a boat with a 888 mercruiser (302) in it. It seems like it won't run above 100F. Figured the thermostat was stuck open, so I replaced that and it still runs cold. Pulled the thermostat and checked it in a pot of water and it starts to open at 140 like it is supposed to. Found that the previous owner had mixed up manifold return lines with the riser feed lines where they connect on the thermostat housing. Fixed that, it still won't go above 100. Doesn't seem to matter if it is running on the hose or in the lake. Not sure if it would matter but it is supposed to be an early 90's mustang block in it, with a marine cam. Right before I got it, the waterpump impeller failed, I was expecting to find a chunk of rubber stuck in the thermostat, but I haven't seen any pieces of it anywhere. I would expect it to run too hot if rubber debris was jammed in a cooling port somewhere. Any thoughts?

 

[Scott Danforth]

first, welcome aboard

are you relying on the dash gauge, or are you verifying with an IR thermometer?

 

[Scott06]

As mentioned would verify temp is accurate first

Any blockage from a spent impeller would raise temps not lower them

If it is low given your comment on cooling line mix up would verify that the cooling water flow is correct as to run too cool you would have to have water flow bypassing the thermostat

Using a former mustang engine is fine as long as it was marinized cam freeze plugs head gaskets and circulation pump need to be marine, plus all the accessories for fuel and electrical components

 

[atuomi]

Forgot to mention in the initial post that I did confirm temp with an IR thermometer. Triple checked cooling lines with pictures of other 888's and the system schematic that is online.

There isn't supposed to be a restrictor in the bleed hole in the thermostat housing? I wouldn't think you would want it too small as that would limit water getting dumped into the risers when the thermostat is closed. Unless I'm not understanding how it works.

 

[Scott Danforth]

the thermostat is used as a mixing valve. constant flow to exhaust, with cycling flow to the motor

make sure the spacer is in there

 

[kenny nunez]

If the by pass hole in the thermostat housing has been enlarged that could be the reason for running too cold.
There are several advertised on google search.
Do you know if the correct stainless plates are between the risers and manifold bodies?

 

[atuomi]

the thermostat is used as a mixing valve. constant flow to exhaust, with cycling flow to the motor

make sure the spacer is in there

I'm not sure that theres anywhere for a spacer to go in this housing. If you are referring to the plastic sleeve that sits on top of the thermostat? I have seen that before in a 3.0L merc but this one is different than that.

 

[atuomi]

If the by pass hole in the thermostat housing has been enlarged that could be the reason for running too cold.
There are several advertised on google search.
Do you know if the correct stainless plates are between the risers and manifold bodies?

The hole doesnt look like it has been drilled out. I'll see if I can find a spec for the size that it is supposed to be. Not sure which plates are in the manifold/riser. Some of them let water flow between and some are blocked off correct?

 

[kenny nunez]

The stainless plates are supposed to have a small bleed hole to keep air pockets from collecting in the manifolds. Just look closely at the mounting area and if a stainless plate is there, if so then there will be 2 gaskets on either side of the plate.
If my memory is correct the bleed hole in the housing will be 1/4”-5/16”.

 

[atuomi]

Looks like there is no stainless plate between the manifold and riser. I just see 1 gasket, about 1/16" thick. Without the stainless restrictor plate, is water from the manifold going straight into the riser and then dumping into the exhaust?

 

[atuomi]

Ordered restrictor plates and new gaskets. Installed and it runs at 140 now. Thanks everyone for your help.