White dirty sludge in thermostat housing

D

ddclapp

Cadet
Joined
Jun 8, 2010
Messages
28
Hi all,

1984 Mercruiser 260, FWC.

I was having some overheating problems and decided I needed to replace the thermostat. When I opened it up, it was almost completely clogged with a white clumpy (almost crystal) like substance. I chalked this up to not having replace the thermostat for going on 5 years (if it ain't broke, don't fix it). So I cleaned it out, completely flushed the system and filled with fresh coolant.

A week later, I decided to add a overtemp temp switch into the thermostat problem (I wanted to do this for a while, not related to the issue) - I had to remove the thermostat housing again and noticed there was already considerable build up of this same substance. Bits and pieces were coating the inside lower portion of the housing.

I have only replace the thermostat once before and do not remember a build up like this. Is this at all normal or it indicative of another problem?
I am worried that maybe I am getting saltwater into the FWC system through the heat exchanger or elsewhere (i.e. engine block).

Thanks in advance for any advice.

Dan
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,745
ddclapp said:
Hi all,

1984 Mercruiser 260, FWC.

I was having some overheating problems and decided I needed to replace the thermostat. When I opened it up, it was almost completely clogged with a white clumpy (almost crystal) like substance. I chalked this up to not having replace the thermostat for going on 5 years (if it ain't broke, don't fix it). So I cleaned it out, completely flushed the system and filled with fresh coolant.

A week later, I decided to add a overtemp temp switch into the thermostat problem (I wanted to do this for a while, not related to the issue) - I had to remove the thermostat housing again and noticed there was already considerable build up of this same substance. Bits and pieces were coating the inside lower portion of the housing.

I have only replace the thermostat once before and do not remember a build up like this. Is this at all normal or it indicative of another problem?
I am worried that maybe I am getting saltwater into the FWC system through the heat exchanger or elsewhere (i.e. engine block).

Thanks in advance for any advice.

Dan
Click to expand...

At the start of your post you used FWC and I would take this as fresh water cooled. Then you go on and say you filled it with fresh coolant. I'm now going to figure you have a closed cooling system which uses antifreeze. With closed cooling it sounds like your mixing regular ethylene glycol (green stuff) with Dex-cool (orange stuff), or the other way around. You can't mix the stuff, it will clog everything up.
 
Last edited:
Fun Times

Fun Times

Moderator
Staff member
Joined
May 16, 2009
Messages
9,150
D

ddclapp

Cadet
Joined
Jun 8, 2010
Messages
28
Thanks for the suggestions. Yes, a cooling system with antifreeze. I had not changed the coolant for probably 4 years. This time, I completely flushed (pulled drain plugs on both sides of the engine, ran the hose from thermostat housing out the plugs. Hopefully then it is just sludge from old coolant. I did not mix brands, but used the same green coolant I have always used. One note: this all started with boiling over from the heat exchange, which was an indicator that the thermostat needed fixing.
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,745
Probably just crud, so your flushing should help take care of it.
 
You must log in or register to reply here.
Top