Sea Trial Question

[SpilledBEERMayday]

Hello all,

I am getting ready to purchase a 1998 Maxum 2300 SC with a 5.7 Merc Magnum in it. This was upgraded from a 5.0 years ago. My surveyor told me that during my sea trial to put the boat in reverse and see where the RPM's limit to. He said the engine should limit in the 1800 to 2200 RPM range. I did exactly that and sure enough...it stopped climbing around 2000 RPMS....problem is that the engine temp alarm came on immediately after. We shut the motor off and put it in neutral and gave it some gas to circulate some water into the engine. Temps came back down and then we resumed the sea trial with no problems the rest of the ride. The guys were kinda scratching there head why my surveyor would want me to do that and what that would prove.

Before that we had been cruising at near top speed for 15 minutes with no issues and normal temps. After engine was cooled down...we got the boat underway again and no issues for rest of the ride at top speeds.

Any idea why the engine would overheat when putting it top speed in reverse so quickly? Any idea what this would prove from a surveyors perspective?

 

[tpenfield]

Going in reverse at those elevated RPM's most likely ventilated the prop causing an air pocket around the lower unit where the water inlet holes are. So, the engine did not get any water for what ever amount of time that was (presumably only 5-10 seconds :noidea: )

Was the temperature riding high to begin with? If you were running the boat at cruising speeds and then stopped to perform this 'back-up' test, keep in mind that the temperature within the engine surges a bit, due to the lower cooling flow at idle speed, so adding some air into the mix only made matters worse.

 

[aerobat]

i have a 2010 searay 240 sundancer with a 5.0 mpi and assume i would flood my cockpit via the entry door when going 2000 rpm in reverse - never tried this . i did not even knew there is a rev limiter in reverse !