overheating while off idle

[tide me over]

I have a 1985 Regal 200XL with a 1986 3.7L 170hp merc with Alpha 1. If I'm at idle or just above boating 5mph(no wake) she runs cool but when I try and cruise or WOT my temp gauge climbs up until I come back down to idle or no wake and then it cools off in a few minutes. Any suggestions before I throw parts into it. I had my boat idling in my slip for approx 20-25 minutes the other day in mid 90 degree ambient temps and the temp was cool as a cucumber but, as I pulled away it only took 2-3 minutes to start climbing. Any thoughts would be appreciated.

 

[xxxflhrci]

Re: overheating while off idle

I'd make a guess that your lower unit's water pump impellor needs replacing. You can get just the impellor or the whole service kit from NAPA.

 

[tide me over]

Re: overheating while off idle

Do you know if there is any difference with that water pump job on the Pre Alpha sterndrive. I had an older Searay with a Pre Alpha drive and had replaced that waterpump several times over the years. However, when I wrapped a bag in the water or whatever to ruin the pump I ran hot always, not like this problem.

 

[SpinnerBait_Nut]

Re: overheating while off idle

Mercruiser/Volvo/OMC I/O and Inboard forum.

 

[Bondo]

Re: overheating while off idle

Do you know if there is any difference with that water pump job on the Pre Alpha sterndrive.

Ayuh,.... They are essentially the Same....

 

[tide me over]

Re: overheating while off idle

anyone have any other ideas? I changed the waterpump today and have the same problem. Still running hot when I plane and cruise but she runs very cool while I'm idling or in a no wake area. I also changed the Coolant before the season and replaced the radiator cap but, did not replace the T-stat. I would think if it were the t-stat it would get hot as it warms up and stay hot???

 

[chiefalen]

Re: overheating while off idle

clogged riser,manifold.engine mounted water pump vanes gone.

 

[bomar76]

Re: overheating while off idle

Also being the dreaded 470, it could be a clogged heat exchanger.

 

[chiefalen]

Re: overheating while off idle

u got power steering?

 

[tide me over]

Re: overheating while off idle

Yes this boat does have Power Steering.