Do I need a new Thermostat

[Bigplumbs]

Had a nice day out today in the Fletcher GTS but the engine temp seemed to be odd. This is only my second outing so I don't know what to expect. The engine as most of you know is a mercruiser 3 ltr. When I was just pootleing along at very low revs the temp was at the bottom of the gauge (This makes me think the stat is jammed open) Then after a while at about 4500 revs (Sort of flat out) it got to about 180 degrees. The impeller is good I think. DO you think I should replace the Thermostat or are these sort of temps normal

Dennis

[ColinR]

Doesn't sound normal to me. If it was a car I would say thermostat for sure. I'm sure an engine techy will be along shortly

[Gazjen]

Yea sounds like a stuck open stat, or removed and if it's been removed you need to figure out why.

[Bigplumbs]

I don't think it is removed because I am sure the first few times I ran the engine on water it held at about 140 degrees. I will get one from repower marine. Provided the sleeve that holds it in place is is not seized in I don't think it is too bad a job to replace

Dennis

[betty boop]

easy job, mine took a few outings to settle down and show a constant temp after i changed it. Not sure if thats normal but it did cause a few phone calls and investigations that proved fruitless when it all went 'normal' a few weeks later.

[BruceK]

Are you raw water cooled?

[Bigplumbs]

Are you raw water cooled?

Yes indeed

Dennis

[BruceK]

In that case, it is my experience that they do tend to run cool at low power output but hotter on higher power than those with intercoolers. Why this should be so is a matter of lengthy debate and you'd think it would all be controlled by the thermostat, but it just isn't. Particularly if the boat has been used in salt water and has a few years on the clock. By all means change the thermostat, it's a simple quick job, but don't be distraught if it doesn't cure it. My 3.0 GL worried be endlessly at first, but she never boiled over.

Some argue that salt water corrosion builds up in the cooling ducts creating slower flow and insulation. This may be true, but cast iron doesn't rust through (just look at all the Victorian piers, they have a self galvanising effect). Running hotter causes some owners to have a knee jerk reaction and remove the thermostat altogether. This isn't really advisable. So long as the water isn't boiling the engines prefer it hotter.

[Bigplumbs]

Many thanks Bruce. I have ordered a new stat but will give it a few more tests to see if it needs it yet

Dennis

[mlines]

Our 3.0 mercruiser would get up to a working temp of around 180 and would fluctuate around this going to 195 when pressed if I recall correctly

Sent from my Nexus 6P using Tapatalk