Overheating issue

[rhino4552]

Hello all, Ive got a 1990 omc 5.7 cobra. Since it came out of winterization, it has been having a strange temperature problem. With the boat at idle in the driveway (muffs on), it will climb to around 150, and stay there. At the lake, after running at speed for about 30 minutes the temp will still be around 150. After this point, the temp will slowly rise up to around 200. Then it will go back down to 150 randomly. Then climb back up to 200. The highest it has gone is about 210. The gauge goes to 240. It seems like it goes down when giving it more throttle, but it very difficult to tell. It will continue to move the entire time. The thermostat was replaced a year ago, and impeller replaced two weeks ago. The needle is not jumping, it is slowly rising and falling.

Suggestions?

 

[DBreskin]

Re: Overheating issue

Maybe your thermostat is not working properly?

 

[Stanp1]

Re: Overheating issue

Hello all, Ive got a 1990 omc 5.7 cobra. Since it came out of winterization, it has been having a strange temperature problem. With the boat at idle in the driveway (muffs on), it will climb to around 150, and stay there. At the lake, after running at speed for about 30 minutes the temp will still be around 150. After this point, the temp will slowly rise up to around 200. Then it will go back down to 150 randomly. Then climb back up to 200. The highest it has gone is about 210. The gauge goes to 240. It seems like it goes down when giving it more throttle, but it very difficult to tell. It will continue to move the entire time. The thermostat was replaced a year ago, and impeller replaced two weeks ago. The needle is not jumping, it is slowly rising and falling.

Suggestions?

Couple things to start with, buy an infrared temp gun from an auto parts store. Never trust your gauges. if the temp holds stead on the Infered gun, then you have a bad sending unit or guage(or both)

If the gun is showing the same thing as your temp gauge, you have a water flow issue. Start with inspecting your impeller. if chucks are ripped off, or it hasn't be changed in a while, replace it. Be sure to clean out the raw water hoses and oil coolers along the way. How old are the exhaust mainfolds? they might be brittle inside and not alowing heat to disapate fast enough.

That aught to keep ya bussy for a while.

 

[cr2k]

Re: Overheating issue

2 GAUGES that are unreliable in a boat are the fuel gauge and the temp gauge. But this doesn't mean you don't have other problems.