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View Full Version : Thermostat replacement 351 Indmar


mjdavis
09-01-2012, 09:32 PM
Hi guys,

My old thermostat was periodically sticking so I ordered a new one from Skidim. I installed it today and the first time I started the engine the temperature slowly rose all the way up to the alarm point at around 220 or so. I was puzzled and thought maybe I put it in wrong so I pulled it out, flipped it over and reinstalled it. The same thing happened.

What am I doing wrong? Is the pointy side of the thermostat supposed to go up or down? It's a 143 degree unit.

Any ideas?

jfw432
09-01-2012, 10:25 PM
Are you sure it's the thermostat that was sticking? It's really easy to confuse a thermostat problem with a failing raw water impeller problem. Take a look at your impeller. My bet is it's toast.

Voodoo
09-01-2012, 10:28 PM
Was the cooling system behaving normally before the replacement?

If not, the impeller may be gone.

Was water exiting the exhaust pipes?

Every once in a great while I'll have to jack the throttle to initiate water flow while running the motor in the driveway.

Run it without the thermostat and verify it does not overheat.

Voodoo

mjdavis
09-02-2012, 12:54 AM
I've got good water coming out of both exhaust ports so I don't think its the impeller. Also, the system seemed to act normal with the exception of occasional sticking of the thermostat that allowed the temp alarm to go off maybe once or twice during a two to three hour period of skiing/boating time.

I'll try running it without the thermostat to see what happens to the temperature.

Is it possible that the new thermostat I got is bad? Will I be able to tell something if I put it in a pot of water that is heating up on the stove?

jfw432
09-03-2012, 02:17 PM
Yes you can test a thermostat by boiling it on the stove. Yes you can run the engine without a thermostat but I personally wouldn't unless I was stranded on the water. Those rubber impellers fail so frequently that everyone I know carries a spare in the boat, if that tells you anything... IMO, it would take the same amount of time to pull the thermostat and boil it as it would to pull the raw water impeller and look at it.

Part of the problem with worn impellers is they seem intermittent. If everything is working halfway and you're running the boat at cruising speeds (ie not WOT and not idling) a worn out impeller still works fine. If you flush your boat after using it and turn off the water and leave the engine running a few seconds longer, this partially or completely drains the water from the lines. The lack of water in the system makes it impossible for a worn impeller to achieve good primed lines so the engine doesn't get water.

Making things more complicated and intermittent... If you have a lot of people in your boat or start it on a steep ramp, you have effectively partially primed your cooling lines making the worn impeller work this time but maybe not next time.

mjdavis
09-06-2012, 04:48 PM
Quick summary... My thermostat was bad AND I needed a new raw water impeller. From observation it wasn't surprising the thermostat was sticking but the impeller looked fine and all vanes were intact. However, when I pulled it out for a thorough inspection I noticed that the rubber was quite soft. I put in a new impeller and the system now works perfectly!

Lesson learned (which has been posted in here many times) is to replace the raw water impeller annually whether you think it needs to be done or not!

mikeg205
09-06-2012, 05:53 PM
Quick summary... My thermostat was bad AND I needed a new raw water impeller. From observation it wasn't surprising the thermostat was sticking but the impeller looked fine and all vanes were intact. However, when I pulled it out for a thorough inspection I noticed that the rubber was quite soft. I put in a new impeller and the system now works perfectly!

Lesson learned (which has been posted in here many times) is to replace the raw water impeller annually whether you think it needs to be done or not!

Outstanding post!