Over heating problem. need help

[tkms002]

I have a model year 2000 200 EFI Mercury outboard. This past August I was on Sturgeon bay and the water temp was in the low 70s. I was just cruising along a about 3000 RPM and the over heat warning horn came on. I looked at the temp gauge and sure enough it was at about 210 degrees. The motor was peeing well and the water pressure gauge was reading about 12 psi at that 3000 rpm.
I replaced the thermostats and the water pump and had it out on a local lake with a water temp of 57 degrees this past week to do some testing. Ran a mile or 2 at 3000 RPM and the temp gauge again read 210 degrees but the warning horn did not go off. Probably just short of tripping due to the colder water.
Running at ANY other RPM will cause the motor to cool off. I can run miles at 4000 RPM or at 2000 RPM and the engine stays cool(145 or so).
Looking for any ideas.
Thanks

 

[Chris1956]

So it overheats at 3000 RPM and not at 2000 RPM or 4000 RPM? Maybe the poppit valve is sticky, and the water pressure at 3000 RPM is not enough to open it? A guess....

 

[tkms002]

My understanding of the poppet valve function is to allow excess water pressure to be dumped directly to the exhaust. I imagine if it had a week spring and was opening too soon it could cause this problem. If I am wrong with this someone please correct me.

 

[racerone]

Wrong.-----It puts more water through the engine for cooling at higher RPM.

 

[Chris1956]

Replace the poppit valve with the exact one from your motor. They have changed over the years.

 

[tkms002]

Replace the poppit valve with the exact one from your motor. They have changed over the years.

I replaced the poppet valve and all its various parts. I have not had time yet to test it but the old poppet valve looked practically pristine. I dont think that is the problem but we will see when I get out to test it. Hopefully there will be a day before ice up. LOL

 

[tkms002]

one thing I have not mentioned. I have a water pressure gauge and it shows a constant 12 psi at 3000 rpm but at 4000 rpm the pressure varies wildly from as little as 5 psi to about 10 psi but it runs at about 145 degrees at 4000 rpm.

 

[racerone]

Check height of transom.----Perhaps motor is mounted too high.----Long shaft motor on a boat that needs extra long.

 

[Dukedog]

sometimes in tha poppet tha plastic disc will get slightly "warped".. you will not notice it unless ya lookin' for it.. we built our own from alum. stock ta replace tha plastic.. that can cause what your experiencing.. if ya put new parts in it maybe that was it???

 

[tkms002]

I will try to get it out on the water this week

 

[tkms002]

Well I got it on the water today. Water temp as 47 F. Ran the boat(after letting it warm up) at idle for a quarter mile and the temp topped out at about 150 ish then ran it up to 2000 RPM for 10 minutes or so and the temp topped out about 180 ish then ran it at 3000 rpm and them temp climbed to about 210 ish(no warning horn). Then I ran it at 4000 rpm and it cooled back down to 150 ish. I think of the water temp as near 80 it may have sounded the warning horn at 3000 rpm. So, this issue seems to persist after changing the poppet valve and all its parts.
Any thoughts are welcome.
Thanks

 

[Sea Rider]

Check the water pump, impeller, heat sensor, thermos and their housing condition if excessively salted/crusted. Proper time to install new ones in if found shot...

Happy Boating​

 

[tkms002]

Check the water pump, impeller, heat sensor, thermos and their housing condition if excessively salted/crusted. Proper time to install new ones in if found shot...

Happy Boating​

t-stats, impeller and poppet have all ben replaced and all the passages you can see when doing those chores look clean.

 

[Chris1956]

Water pressure should build as motor approaches 2000RPM, poppit should then open and water pressure will likely level off.

If that is what you are seeing, then I am not sure what your issue is.

However, If the water pressure drops at 3000RPM, then it sounds like something inherent to running at 3000RPM. Air being sucked into the engine, or a vacuum made by a keel or fishfinder transducer, at that RPM.

Not real helpful, I know.

 

[tkms002]

Water pressure should build as motor approaches 2000RPM, poppit should then open and water pressure will likely level off.

If that is what you are seeing, then I am not sure what your issue is.

However, If the water pressure drops at 3000RPM, then it sounds like something inherent to running at 3000RPM. Air being sucked into the engine, or a vacuum made by a keel or fishfinder transducer, at that RPM.

Not real helpful, I know.

ya I know its a tough one. water pressure is stable at 3000 RPM at about 12 psi but the temp builds to close to 210. Water pressure drops at higher RPMs but then the temp falls back to <180 and at some RPMs as low as 150.

 

[Chris1956]

Cylinder head gasket leaks can cause overheating. A compression test might show it. Of course, it would overheat at high RPM also.

 

[Dukedog]

jus sounds like it has something ta do with tha poppit???.. did ya check tha "staked" bushing in tha block.. its not supposed ta rotate at all.

 

[tkms002]

jus sounds like it has something ta do with tha poppit???.. did ya check tha "staked" bushing in tha block.. its not supposed ta rotate at all.

the bushing is tight. I could not pull it out so I did not replace it even though I had the part/

 

[Dukedog]

callin' computer "calf rope" with this problem!

 

[tkms002]

callin' computer "calf rope" with this problem!

say what??