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Thermostat Questions

Sep 7, 2018
7
Catalina 30 Fish Sticks Marina
I have a couple questions about the thermostat in my Universal M18.

1. It has a coolant bleed valve on top of the thermostat housing. When you turn it it will either go higher or lower. Which way is it supposed to be (up or down) when running the engine and which way when bleeding the coolant?

2. I'd like to remove the thermostat. Is there anything I need to do before removing the bolts on the housing? When I turned the bolt I heard some air coming out and decided I better check to see if there's something I need to do before removing those.

3. What do I need to do when reinstalling the thermostat housing? Any burping or bleeding of the coolant. If so how? Thanks!
 
Feb 5, 2004
3,933
Tartan 3800 Westport, MA
I'd like to remove the thermostat.
Why? You don't seem to know much at all about cooling systems, but you want to remove the thermostat. Not a good idea. It's there for a reason.
 
Sep 7, 2018
7
Catalina 30 Fish Sticks Marina
Why? You don't seem to know much at all about cooling systems, but you want to remove the thermostat. Not a good idea. It's there for a reason.
Thanks for the insult.

My engine is running hot and I'm not getting the water flow I want out the stern. When I go around 1300 to 1500 RPM the engine goes over 200 degrees. My engine is supposed to run at max 190 degrees at around 2200 to 2600 RPMs. The water comes out but it's not constant. I replaced the impeller (because it was recently destroyed) and flushed the heat exchanger (to flush out any bits of impeller) and it helped but it still runs hot.

I discussed this with another boater (who has a diesel engine) and a marine mechanic (who by the way knows a lot about cooling systems and works on marine engines daily) and they said to check the thermostat. The other boater did this on his boat and it fixed his overheating problem. So keep your insults to yourself and just answer the questions if you can.

Don't reply unless you can answer the questions smart guy.
 
Feb 5, 2004
3,933
Tartan 3800 Westport, MA
Is the engine coolant full?

My guess is insufficent raw water flow.

That is probably the most common cause of the symptoms you describe.

Are you sure there's no clog along the way? The heat exchanger is really clear? Any pieces of impeller in hoses or heat exchanger?

You can measure raw water flow by catching the exhaust water in a bucket, and timing it.
 
Feb 5, 2004
3,933
Tartan 3800 Westport, MA
On the thermostat housing vent, it's my recollection that it's a left hand thread, and screws down to the keft to open; but my recollection may be faulty.
 
Jan 5, 2017
1,299
Beneteau First 38 Lyall Harbour Saturna Island
Thermostats do fail. I’ve replaced mine. Drain some coolant from the heat exchanger then the two bolts that hold the thermostat housing, remove thermostat. You can check it by putting it in cold water and heating it and watch it open. My old one only opened part way so I replaced it. All is well now.
 
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May 20, 2016
2,804
Catalina 36 MK1 Everett, WA
If your flow is erratic it’s probably not the tstat. What condition is the pump cover in? If groved you won’t be moving enough water. You could still have impeller chunks impeding flow. How do the tubes in the HE look? Is it time to be rodded out?? Intake unobstructed??

Note the tstat does not effect the flow of raw water cooling if you have a heat exchanger. Go where the clues take you. Fix the flow problem first then if still having issues look at the antifreeze side.

Les