454 Bravo 1 engine overheats on first run only then works fine
 

I have Mercruiser 454 with bravo 1 it's 1999 with only 55 hours on it, it was in storage for 6 years, last 2 times I took it out, the engine overheated to 210-220 then turned it off, I lifted the engine to check if the lower drive intake was plugged up but it was fine restarted and went back to 170 worked great for the next five days.

After 2 weeks I took the boat out and same thing happened, on the first run about 10 minutes the engine started to over heat I shut it off at 210 before the alarm went off. lifted the outdrive to check for blockage seems fine restarted the engine and went back down to 170.

Any ideas or advice what could be causing the overheating.

sam

replace the thermostat

Plan B , drill 4 , 1/8 inch holes in the stat.

Replace thermostat, it's sticking.

If replacing the stat doesn't help , it's likely an airpocket by the stat during intial warm up causing the over heating problem since the stat is NOT in water. 1/8 inch holes vent the air and allow water to hit the stat and the problem will disappear.

I've been having this problem too, with brand new t-stats. Gonna vent my stats and try it out this weekend...

But how do the engines get air pockets?

Plan C: remove the thermostat altogether. If it is a T-stat related problem, it will end with its removal.
Added bonus: you will run cooler temps.

If it's a fuel injected engine, it needs a thermostat. It's a 160 degree I think. If it's a carb engine, use a 140. Drilling vent holes is a good idea. Is your impeller fresh?

if you really believe the tstat needs a vent ( unlikely altho there are some factory ones that have a .090 hole w /a flapper in it ) drill ONE 1/8 hole. anything more than that both changes the temp calibration and often makes it not work at all.

not certain why people are so willing to believe that multi billion dollar companies with hundreds of REAL engineers that actually know what they are doing and turn out a trillion thermostats a year for the last hundred years might not have NOTICED that they have been making them wrong all this time... but i suppose thats just me being naive enough to think they might actually know what they are doing.

OHHHHH i forgot... this is MARINE stuff... so everything is MAGIC...

You hit the nail on the head:angry-smiley-044: