Overheating 3.0 Merc..

[DayCruiser]

3.0 Merc Cruiser 1989 engine. On top of my other problem. After about 30 minutes of the maiden voyage of the new season, the boat started runner hotter than usual. The first 30 minutes it would reach the thermostat 160 degree temp and then drop back to 158. So I could see the thermostat was working properly. After the 30 minutes, it started climbing to 180 for short idles. I didn't waite to see if it would go higher and it was pretty consistant at going toward 180 for the last 30 minutes of the trip. Then at WOT, it would drop back down to 158. How hot is too hot? I think last year it ran like this on the first trip out too and then went back to normal
Impeller and thermostat were changed 3 years ago and it hasn't been ran out of water

 

[rndn]

Re: Overheating 3.0 Merc..

Sounds like it's time for an impeller replacement.

 

[DayCruiser]

Re: Overheating 3.0 Merc..

Ya I agree. Looks like the impeller only had 30 more minutes of life lol grrrrrrrr

 

[chiefalen]

Re: Overheating 3.0 Merc..

change out the thermostat 3 years is about the life in saltwater.impeller might be bad but the engine mounted water pump could be bad if never changed out thats where my money is that its bad.

 

[chiefalen]

Re: Overheating 3.0 Merc..

have you ever had the riser off? sometimes there is an obstruction in the exhaust.could be a flapper broke loose?could be rust in the thermostat housing.alot off people change out the thermastat every year.good luck

 

[DayCruiser]

Re: Overheating 3.0 Merc..

I had the riser off when the block cracked a few years ago. I will start off by changing the thermostat and then go from there. Thanks for the suggestions!

 

[wkb2460]

Re: Overheating 3.0 Merc..

I just sold my 1987 3.0 Merc. Owned it for six years and had the exact same problem for every maiden voyage of the season. I'm no expert, but I chalked it up to rust.

 

[DayCruiser]

Re: Overheating 3.0 Merc..

Well it kept going up to 180 so I took it to the shop Friday. Also he is going to repair the upper reverse throttle cable(connects to the command shifter). Should have it back late next week. Like pulling a tooth for me to take it back out so soon