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wats218
07-14-2011, 07:24 AM
Took the boat out last night (96 prostar 190 with GM 350). Got her up to 4000 rpm and then rpms quickly dropped to 1000. Slowly increased rpm again, got to 2000 then it quickly dropped back to 1000 again. Couldn't get it past 2000 at this point. Engine seemed to be running hot, around 200. What is the normal running temp? I have a 160 deg thermostat. Is there a temperature safety cutoff that could be dropping the rpms to protect the engine? I also felt the hoses coming out of the thermostat housing. The house from the raw water pump to the thermostat was hot and the hoses from the thermostat to the exhaust manifolds were cool. Could this just be my thermostat isn't opening fully? Took the thermostat out and it was only partially opened, temp sensor still read 200 at this point.

Looked at the impeller, looked fine. Checked for blockage from water intake to external pump, everything ok. Ran garden house in hoses from thermostat to exhaust manifolds and water poured out of exhausts. Seams like water flow is ok, thats why i'm focusing on the thermostat.

ntidsl
07-14-2011, 07:56 AM
Sure seems like you are on the right track to me. Glad to see you are watching your guages closely. Well done...as long as you havent done any other recent work on your boat I'd say thermostat. But then again you know that already sounds like.

rhsprostar
07-14-2011, 09:48 AM
Sounds like the thermostat. Cheap and easy fix, buy a new one and toss it in. That way you will know.....

wats218
07-14-2011, 10:13 AM
Going to try to run it with a new thermostat Friday. Just wanted to see if dropping rpms made sense with an over heating engine. Thanks guys.

wats218
07-14-2011, 12:58 PM
What temp does your boat normally run at?

xbot50000
07-14-2011, 01:14 PM
160 - 03 Mcx

rhsprostar
07-14-2011, 01:17 PM
just a tad over 160......

woodrowskis
07-14-2011, 01:32 PM
boat should run about 160-165. If you are running pretty hard and then drop to idle, the sudden decrease in water flow will let the temp jump from 160 up to about 180 for a couple minutes as the higher rpm heat was not fully dissipated yet. But then it should creep back to 160 at idle as well. Anything higher than that, something is off.

wats218
07-17-2011, 03:53 PM
Ran the boat Friday without a thermostat. Ran great. Temperature never went above 120, but alteast I know the overheating was what was causing me to drop rpms. Going to throw a new thermostat in it and we should be good. Thanks for your help.

Jerseydave
07-17-2011, 04:32 PM
Ran the boat Friday without a thermostat. Ran great. Temperature never went above 120, but alteast I know the overheating was what was causing me to drop rpms. Going to throw a new thermostat in it and we should be good. Thanks for your help.

Hey where have you been running? Hope to catch up with you sometime on the river.

Anyway, your engine protected itself by going into limp-home mode since it was reading a high temp. Do you have the LT-1 engine? If so, I think I read on here that you may have 2 thermostats? If you don't have the LT-1 then only 1 thermostat.

Glad to hear you found your problem.

wats218
07-17-2011, 04:41 PM
Hey Dave. We actually just started running in the Mullica River near Sweetwater. Starts out as brackish water then turns to salt. I'm hoping that this thermostat issue is the last of our problems. We're on vacation in 2 weeks so we'll definitely find out then.

We don't have the LT1, but thanks for the heads up.

Jerseydave
07-17-2011, 05:33 PM
Hey Dave. We actually just started running in the Mullica River near Sweetwater. Starts out as brackish water then turns to salt. I'm hoping that this thermostat issue is the last of our problems. We're on vacation in 2 weeks so we'll definitely find out then.

We don't have the LT1, but thanks for the heads up.

I ran that river for 2 years, but it gets too crowded on the weekends and the green heads are killers! Drag that boat to Florence sometime and hit the river with us! I'd be glad to show you any trouble spots (not many BTW)