Odd overheating problem

[SCOTTDOMINE]

So to explain the situation a little, I just serviced the Bu (new impeller, cleaned screen, fuel filters, plugs, wires, cap, oil, trans fluid change, etc..) Just yesterday we started to get a little bit of an overheating issue only when up to speed? At idle and low speed cruising all was normal, but when half or a little more throttle the temp was rising to around 200-220. Figure it could may be the thermostat? Any help would be greatly appreciated.

[skier92]

When cleaning the trans cooler, did you take hoses of both ends and do a visual with a light? Easy to miss small stuff. Next, I'd check for leaks at the any of the hose connections or water pump and if still nothing, then I'd check the thermostat.

[dm1]

So to explain the situation a little, I just serviced the Bu (new impeller, cleaned screen, fuel filters, plugs, wires, cap, oil, trans fluid change, etc..) Just yesterday we started to get a little bit of an overheating issue only when up to speed? At idle and low speed cruising all was normal, but when half or a little more throttle the temp was rising to around 200-220. Figure it could may be the thermostat? Any help would be greatly appreciated.

Just wondering if you ever figured out the problem. I have the samething going on with my boat. (98 sportster) With the stat in temp will rise to roughly 220 (by my guage) then drop to 140, when I take the stat out temp will stay at 110 or so.

[nuttyskier2002]

So to explain the situation a little, I just serviced the Bu (new impeller, cleaned screen, fuel filters, plugs, wires, cap, oil, trans fluid change, etc..) Just yesterday we started to get a little bit of an overheating issue only when up to speed? At idle and low speed cruising all was normal, but when half or a little more throttle the temp was rising to around 200-220. Figure it could may be the thermostat? Any help would be greatly appreciated.

Just wondering if you ever figured out the problem. I have the samething going on with my boat. (98 sportster) With the stat in temp will rise to roughly 220 (by my guage) then drop to 140, when I take the stat out temp will stay at 110 or so.

On more than one occasion I have seen temps climb like this on the first run after a new stat install. After that they start to operate normally. Anyone else notice this?

[krich999]

Having a similar problem. Check out my thread. Have not yet solved the issue, but will let you know when I do.

Krich999

So to explain the situation a little, I just serviced the Bu (new impeller, cleaned screen, fuel filters, plugs, wires, cap, oil, trans fluid change, etc..) Just yesterday we started to get a little bit of an overheating issue only when up to speed? At idle and low speed cruising all was normal, but when half or a little more throttle the temp was rising to around 200-220. Figure it could may be the thermostat? Any help would be greatly appreciated.

[JasonK]

On my mercruiser, the 2 impeller pump hoses can get switched when you change the impeller. Gives symptoms described. I idled out for a while, all was good, but when I took off the temp shot up.

[Sunsetter95]

I would be absolutely sure that the raw water pump hoses are on correct. Double check, triple check if need be.

I have seen new thermostats stick or not operate correctly, but that is unusual.

I would also check the screen of the trans cooler visually as mentioned above.

If the issue continues, start looking at the hoses from the bottom of the boat to the exhaust. I had a hose that collapsed on the inside. The more water that needed for the engine (increased RPM) the more the hose restricted the flow. It was the raw water hose between the bottom screen and the raw water pump. That was a tough one to pin down.

[Woodski]

Might also be the type of stat you installed. A marine stat actually will constantly bleed some water past itself. If you installed an automotive stat, simply drill a couple of small holes on the outer edge of the stat to bleed water past until it opens.

[dm1]

eventually found the problem, it was the circ pump on the motor. The impeller snapped in two. I guess the raw water pump was enough to handle the heat load of the boat, which explains the wide range in temps (140-210) As a side note, this is an excellent site with very helpfull people, but most people post and run. If you read thru alot of the posts, it is rare that the op goes back and tells what the solution was. It would be greatly appreciated by many if people would tell the end result. Thanks...

[Woodski]

Was that a plastic impeller in the pump?

[dm1]

Was that a plastic impeller in the pump?

It was metal, it looked like brass.