Thermostat issues ?? never got above 120 degrees

Mark T · **Posted:** Mon May 21, 2012 12:12 pm

Ran the boat on Lake Michigan, water temp about 55-60. thermostate never got above 120 ?? is it not functioning, or is it because the water is too damn cold ?

ric · **Posted:** Mon May 21, 2012 12:32 pm

Marine thermostats are cheapo junk. When they "break" they break closed and overheat the engine. Well, like 99% of thermostats on the market for cars and boats do. They don't make safety thermostats for boats that I've seen.

Are you sure you have one in there? I ran without one for a quick minute and yep... 120 was about all she saw. Rides around 170 with one.

Sanmiam · **Joined:** Sat Mar 24, 2012 9:05 pm **Posts:** 84

Possible the thermostat is stuck open. Would do pretty much the same thing as not having one at all.

Walt · **Posted:** Mon May 21, 2012 4:08 pm

ric wrote:

Marine thermostats are cheapo junk. When they "break" they break closed and overheat the engine. Well, like 99% of thermostats on the market for cars and boats do. They don't make safety thermostats for boats that I've seen..

?????
I've only replaced the thermostat in about 80% of my cars and boats in 20 years of boating, but they ALL failed open, and 120F was the temp that told me it was stuck open.

Now, you can try running it on the muffs and see if it clears. I've had success 2 or 3 times with that (guessing silt/sediment blocking). Otherwise, the T-stat is easy to replace, just make sure you get the right gasket too, and be ready to break some bolts if it's been in a corrosive environment.... can you say anti-sieze?

Sanmiam · **Joined:** Sat Mar 24, 2012 9:05 pm **Posts:** 84

Walt wrote:

ric wrote:

be ready to break some bolts if it's been in a corrosive environment.... can you say anti-sieze?

On that note - if the bolts don't come out w/o too much effort I would soak with PB Blaster a couple times a day for a few days before trying to really wrench them out (or even better - hit it with an impact rather than just a wrench if possible)

Mark T · **Posted:** Mon May 21, 2012 5:18 pm

Perhaps the sandbar we ran aground on, was the culprit for something stuck in there. Bolts look ok, but will hit it with the PB just in case. Thanks for the suggestions

298VISTA2000 · **Posted:** Mon May 21, 2012 5:56 pm

Yep, stuck open.

LouC · **Posted:** Mon May 21, 2012 6:18 pm

I've had this problem every other year or so in salt water. A piece of rust gets inbetween the seat and the stat and it won't close all the way. Even when you run on plane and it gets up to normal temp, sometimes the piece of rust or bit of sand sticks in there. Sometimes when you take em and boil em in a pot of water you can get it to close all the way. I change em every 2 years. Put OMC gasket sealer on the gasket and on the bolts, never any leaks and the bolts always come out even in salt water.

Mark T · **Posted:** Tue May 29, 2012 1:16 pm

Napa dealer across the street from my office had one to me in less than 24 hours from one of their other ware houses. Kind of a pain to change, but not too bad. Should have thought about changing all the hoses, but will do that in the fall since they were not too bad looking.

Thanks for your help

Surface Interval · **Posted:** Thu May 31, 2012 6:11 pm

You may be picking up sand or other particles from the lake water and having that hold the thermostat partially open. I found that with mine. I opened mine up 2 or 3 times and found a grain of sand holding the thermostat open. I finally gave up on it. It doesn't take much to keep the engine from warming up. The 302 EFI Ford/OMC(Volvo) has a 145deg thermostat. I have noticed that if I work the boat like pulling kids on tubes and then shut it down for a few minutes to load kids the engine will "heat soak" and sometimes the thermostat will work correctly again. This may or may not last. While normal operating temp would be nice, mine rarely warms up to that temp.

Technologic80 · **Posted:** Fri Jun 01, 2012 12:49 pm

Surface Interval wrote:

You may be picking up sand or other particles from the lake water and having that hold the thermostat partially open. I found that with mine. I opened mine up 2 or 3 times and found a grain of sand holding the thermostat open. I finally gave up on it. It doesn't take much to keep the engine from warming up. The 302 EFI Ford/OMC(Volvo) has a 145deg thermostat. I have noticed that if I work the boat like pulling kids on tubes and then shut it down for a few minutes to load kids the engine will "heat soak" and sometimes the thermostat will work correctly again. This may or may not last. While normal operating temp would be nice, mine rarely warms up to that temp.

+1

I have twin volvo 4.3's and both of them ALWAYS clog the thermostat open. Usually its particles a little larger than a grain of sand but also pieces of rust from the engine block. I removed the t-stats 3-4x and cleaned the seat of it, just to have it do it again the next ride out. :evil:

Borchik · **Posted:** Fri Jun 01, 2012 1:04 pm

Maybe one time in my 19 years of working on boats have a seen a marine thermostat stick closed...and 90% of them have bypasses in them anyways to allow some flow even if it did stick closed. I would bet for sure it needs to be replaced.

LouC · **Posted:** Fri Jun 01, 2012 3:28 pm

Not only have I never seen one stuck closed, I have never had to replace a thermostat on any of my vehicles that I have owned for the last 35 years or so. I've had to replace water pumps, radiators, but thermostats have not been a trouble spot for me. Some of these vehicles were owned as long as 14 years with over 140000 miles on them. So thermostat failure is pretty rare. The sticking issue is a by-product of raw water cooling. I bet if you had the same engine with closed cooling it would be a non-issue. If and when I re-power this boat it will for sure get at least a half system. Easier to winterize, engine will last even longer (this one is going on 25 years old) and then the engine can run closer to its designed temperature. Honestly I am surprised that raw water cooled cast iron engines last as long as they do. When I replaced the over 20 year old water pump on my 4.3, I was surprised to see that the cooling passages in the block were not really corroded at all and the fact that the pump itself lasted 22 years before the bearing started howling was also a surprise.

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Thermostat issues ?? never got above 120 degrees

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