Merc 5.7 will not get to normal opererating temp

[mr300z87]

Yesterday i took my boat out for what may be the last time of the season, despite my Bravo shifting issue (see my other Thread). Engine ran great all day at normal operating temp around 150 degrees on the gauge as it had all summer. The thermostat was replaced back in July with a Merc 140 degree as per the spec for my engine. Towards the end of the day
went through a shallow spot in the channel and churned up soom of the soft mud on the bottom. All continued normal until I stopped at the dock to drop passengers off. After ideling at the dock for a few min i noticed the engine temp was down near 120 degrees on the gauge where it stayed until i got out of the no wake and was back to cruising speed, 3000RPM 25 MPH when it went back to normal 150 degrees. Back to no wake speed temp dropped back down 120 degrees again all the way to the ramp. I got home and did my normal 10 min run on the hose to wash the salt water out and the temp gauge barely read 100 degrees and he thermostat housing was as cold as the well water coming from the hose. In my experience with cars this problem is usually the thermostat being stuck open. Has any body ever seen this happen before and could a piece of debris have gotten suck up and wedged in the thermostat? Going to pull the Thermostat housing later today and have a look. What else could cause a engine to run cool? All hoses are where the belong!!

 

[Levinz11]

Re: Merc 5.7 will not get to normal opererating temp

I think you have the right idea. I can't think of anything else that causes an engine to run cool.

 

[keith2k455]

Re: Merc 5.7 will not get to normal opererating temp

Same here

 

[mr300z87]

Re: Merc 5.7 will not get to normal opererating temp

I Pulled the thermostat housing off and the thermostat was wedge wide open with sand. I pushed it closed and rinsed now just need the top gasket to put it all back together. My local marine place has it but I don't think I can get there today and they are closed tomorrow Oh well got to work all week anyway so no boating fun!!!

 

[Bt Doctur]

Re: Merc 5.7 will not get to normal opererating temp

most times you can get away with standard chevy housing gaskets. 1 or 2 staples can supply the ground effect.sometimes the mounting bolts themselves supply the good ground for the gauge to work.

 

[mr300z87]

Re: Merc 5.7 will not get to normal opererating temp

Thanks for the reply, I already have the gasket with grounds for the bottom, as I used a Chevy housing gasket when I replaced the thermostat and was going to put the Merc part in when I winterized. The gasket I need goes under the flat plate that goes on top of my housing as I destroyed the new one I put in when the thermostat was done . The old one would probably seal just fine but I want to do it right and am in no rush. Think I will order a couple sets of these gaskets for future use.

 

[Don S]

Re: Merc 5.7 will not get to normal opererating temp

If your temp sender or alarm switch are not mounted in the thermostat housing itself, you don't need the grounding rivets in the gaskets at all. If they are there, only the bottom gasket needs the rivet, the top plate gasket doesn't require one, it's not needed for grounding.