Still Overheating

[SteveG]

I have an 89 wellcraft Nova Spyder twin 454/330's with 400 hrs on the motors and the starboard motor is over heating. Bravo outdrives/ no pump in the lower unit. When I start them the one it always rises to tempature faster than the other and it is by 10 deg while ideling. When I plane off and run the temp difference is by 40 deg, as soon as I come off plane the motor temp drops in about 5 minutes. The alarm system never sounds and it has been up above 200 deg. I have replaced the impellar, replaced the thermostat, cleaned the risers, changed the temp sending unit, swapped the gauges on the panel and still can not figure out the problem. I have flip flopped the thermostats and sending units, no luck. I have pulled hoses to see if the pump is pulling water and the flow looks good. I have no clue on what to do next, I have the mechanical ability to fix it myself if I knew what the problem is. Experience and knowledge required from someone that has dealt with this problem, thanks! <br /><br />All that took place last year. I pulled the Risers and exhausts and was told that they were wasted, rotted away and the Mechanic I have been questioning says that I' extreamly lucky I don't have a wasted engine....never the less I still have a strong motor with a heating problem!!!! <br />I bought new Risers and manifolds, replaced last week. Prior to that I had the outdrives serviced and there was no obstruction that he could see. I have no clue on what the hell to do next. I have inspected the water circulating pump and all the interior parts to that are metal, looks good to my eye. The motor gets hot but not as hot, and it doesn't get as hot as fast. Once again at plane and running is when the heat rises. It use to get up above 200 and no alarm, now it hits just below 200. When I come off plane and go into nuetral it cools back down to the 150 mark. The other motor runs a consistent 150/160 temp. 420 hours on the motor, Chesapeake bay/bush river water ways. Is there anyone out there that can tell me what the hell is the problem??????? Do these engine finally get to a point that they need rebuilt? Getting extreamly desperate!!!!<br />--------------------------------------------------------------------------------

 

[almost retired again]

Re: Still Overheating

Steve have you swapped the therostates from the cool engine to the hot one? It could be that you have a thermostat that is opening too late.<br />Another thought is a possible obstruction in the exaust system, flapper valves have a way of melting and can clog the exaust.<br />These are just thoughts, overheat problems can be a real problem.

 

[steelespike]

Re: Still Overheating

Steve Have you checked plug heat ranges,Checked timing and proper timing advance?Compare plugs cylinder to cylinder For a clue.<br />I like that back pressure idea.Maybe a rubber elbow or connector that is coming apart or collapseing.Check compression cylinder to cylinder<br />engine to engine.Maybe a pair of cylinders are leaking compression into one another.Any chance a water pickup is restricted, bent or sucking air<br /> from some unknown problem at the transom?<br /> Wow did I say all that?

 

[russellackland]

Re: Still Overheating

How old are the manifolds? I had a different motor (F302/Mer888) and did two things that fixed my o/heat prob. One; changed manifolds (big diff) and two; Fresh water supply hose had a narrowing due to a previous repair. I made sure it was the same diameter along the entire length by replacing it.

 

[clanton]

Re: Still Overheating

SteveG post this on www.boatered.com or search there board for overheating your engine and Bravo drive. You are not the only one to have this problem. You have to insure the thermostat housing has a good ground to block for gauges to work. Temp sensor is located in housing. Merc has special gasket with brass rivet for grounding.