05 gravity strange overheating

[jeff 05 gravity]

runs fine first few hours (180 degrees). 2 or 3 hours into the day temp climbs slightly (190?), this happens in just seconds. No alarm sounds, the throttle is still in a forward position but the engine goes back to idle. After 10 to 15 seconds when the throttle is re-engaged, temp drops back to 180 and boat runs great.....for 10 to 15 min. And on and on.

I had this problem at the end of last year and my dealership said they fixed it. I don't remember what, if anything, they said the did.

Just took it out today for the first trip of the year. 3 Hours into the day same problem. Only this time the temp climbed higher(220?). When I put it back in gear the temp dropped back again. The faster I went the more the temp dropped....All the way to 100. Then in a few minutes shot back up to 220 and went to idle.

Anyone have any ideas?

[RED WINE ROCKER]

.....sounds like a thermosat sticking.......when you rev it up, that cracks open the spring....running slow, makes it "unwilling" to open ....they are cheap.

You could pull it out untill you get a new one but all engines are made to run best a certain temp..(...yours 180?)....pulling it out will make it run at a lower than desired temp but......better than frying it.


OR......when is the last time you changed the impeller?

[jeff 05 gravity]

not the thermostat. It will overheat and drop to an idle at ANY speed. The symptom only appears after 2 hours of operation. Then, when it does appear, the frequency between this gets shorter. After the first time it doesn't happen again for 20 min. Then 15, then 10. The next day it runs great for 2-3 hours then starts again.
?????

[wake beater]

I'm having a similar problem with my 1991 Mariah classic (454).If I sit and idle the temp will go to 220 +,but if I drive around at 20 mph or faster it will sit around 130-140.What is the best temp for a 454 to run at?local shop here said the impeller is probably breaking down.

[saltare inverts]

It should run under 150. If it is getting hotter than 200 you can melt exhaust pipes etc. I have done it. If it gets that hot shut her down. My trouble was worn impellar. I replace mine every year now just to be sure.

[wake beater]

It should run under 150. If it is getting hotter than 200 you can melt exhaust pipes etc. I have done it. If it gets that hot shut her down. My trouble was worn impellar. I replace mine every year now just to be sure.

thats what it was 1/2 of 1 fin left out 12 on impellar