Overheating problem Mercury 200 EFI

[pro220]

Has anyone had any overheating problems with 2003 mercury EFI, that you couldn't find the problem. Flushed engine and replaced thermostats. Doesn't do it all the time. Just when you troll for long time and then try to take off. The warning alarm will sound and if you let it idle for a minute it will do fine after that. May not do it again all day or it may do it the next time.

 

[gss036]

Re: Overheating problem Mercury 200 EFI

Could be your poppet valve, but more than likely the impeller needs replacing.

 

[Texasmark]

Re: Overheating problem Mercury 200 EFI

The senario is that the stats open and close to keep the head (at least) slightly above the 143 degree opening temp of the stats. The stats are small and do not allow a great deal of water to pass.

Upon passing through 2500 rpm (I'm told that's the number) or as the ram water pressure enters the lower unit from the boat getting underway the increased water pressure forces the popoff valve off it's seat and the stats are essentially bypassed.

If your poppet it is slow to unseat, that could happen, but it does unseat or you would have a continuous high speed alarm.

I don't know how you get on plane and come out of the "long trolling senario" but it takes time for the water to get from 143F to 195F which is where the OT alarm switch is supposed to close.

Could be the impeller also like gss mentioned.

Poppet is easier to inspect than dropping the lower unit to replace the impeller so I'd start there.

Could be other things, but this is a place to start looking.

Mark

 

[pro220]

Re: Overheating problem Mercury 200 EFI

The impeller has been replaced. The poppet has been checked it to is ok. Just found out that it maybe a oiling problem. Was told that the alarm could also mean low oil level or oil pump problem.

 

[gss036]

Re: Overheating problem Mercury 200 EFI

What does the alarm sound like? BEEP-BEEP-BEEP or constant BEEEEEEEEEEp?
Constant is overheat, beep-beep-beep is oil warning.

 

[pro220]

Re: Overheating problem Mercury 200 EFI

It makes a BEEEEEEEEEEp. Mercury says it could be either one on 2000 and up EFI engines. But they are not much help. Mercury emailed say it could be:1 Cooling system problem :2 Oil level is critically low :3 Oil pump failure :4 Engine over speed or sensor out of range. The EFI uses a Guardian System. I'm going to check the oil system and see what I come up with. Thanks for the help and any other help you can offer. I'll let you know what I come up with.