Overheating - Was It The Thermostat?

TinBoats.net

Help Support TinBoats.net:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

minuteman62-64

Well-known member
Joined
Sep 5, 2014
Messages
110
Reaction score
0
I've got a 1982 30 HP Mariner. Took a run in San Diego Bay this a.m. All seemed normal. Good flow from tell-tale. Didn't notice the exact head temperature, but didn't recall it being excessive (normally shows in the 145-150 degree range, again, on my home made head gauge). Shut the motor down to do some fishing, and, a few seconds later my home made overheat alarm went off. Since the motor was shut down, I figured the thermistor had crapped out so I pulled the fuse to shut it off.

Started the motor and began running at low speed to change location. Noticed the head temperature reading was about 180, but, still strong flow from tell-tale. When I speeded up, the temperature began to drop and got back to the 145-150 degree range.

We fished some more, then decided to cruise by the Spanish Landing area, about 1/2 mile down bay. Same thing with the head temperature, except after a few minutes it wouldn't drop even going at a higher speed. Still strong flow through tell-tale.

Limped back to the launch ramp with a run/shut down/run shut down sequence. Got to the dock with head temperature showing about 200. Running OK, no steam or smoke, still good flow from tell-tale, but definitely way too hot. Let it cool for awhile, then pulled the thermostat. Housing was bone dry, and thermostat was wide open.

Buttoned it up w/o thermostat. Head temperature was still showing 140 degrees, but dropped like a rock as soon as the water started pumping with out the thermostat.

Ran OK to put back on trailer and to flush back home.

Any ideas on problem? New thermostat, last I looked, was about $140. Cheap for peace of mind, but, I'd like to make sure I've zero'd in on the problem.
 
Sounds like you already did that investigation pretty well. If you yanked the thermostat and the temp plummeted when running the motor, then the t-stat was causing a restriction.

It's POSSIBLE that you may have a weak water pump, but I'd guess you're on target with the t-stat. The price you found seems awfully expensive for a t-stat. I did a quick check on MarineEngine.com and the t-stat for a 30 hp mariner is $25. Cheaper if you go for a Sierra brand. And I'm sure you'd be in the teens if you go to Ebay.

Honestly, I'd swap out both the impeller and t-stat and not worry about it from there.

Good luck!
 
I ended up getting one at Boats.net for $62. There is a new replacement part (99080M) that apparently replaces the $140 version I looked a couple of years ago.

I went with Boats.net because I could locate the part based on my motor serial #. Most other sites, for some reason, I can't do this.
 

Latest posts

Top