Merc 470 over heating at WOT HELP

[pop pop]

First off I have a 1986 Merc 470 That the temp runs at 165 % at idle as soon as I give it full throttle the temp shoots right up to over 200 % and blows its top. I have been lucky not to hurt the motor. I have replaced the impeller checked the thermastat witch was bad.It did not open, thought that was the problem and was wrong . Checked the compression it was also fine. Runs great right up until it overheats. I also pulled the exhaust elbow and found alot of rust in the port where the oil cooler connects and the flapper is completly gone. Could this be my problem and do I need the flapper. I realy do not want to overheat again. I should also tell you that I have good water flow through the heatexchanger and no tell tale leak at the motor water pump.PLEASE HELP I DO NOT KNOW WHAT ELSE TO DO!!!!!!!!!!!!

 

[stonyloam]

Re: Merc 470 over heating at WOT HELP

Have you pulled the outdrive? The shutter (flapper) parts could be in there, partly blocking the exhaust. Check the hose from the impeller to make sure it is not leaking or kinked. You might want to pull the end caps off of the exchanger to make sure they are clear. It would be a good idea to replace the shutter. Good luck.

 

[pop pop]

Re: Merc 470 over heating at WOT HELP

Thanks for the info. Just a thought; can you reach the flapper parts from the exhaust on the inside of the engine compartment? If not is the drive hard to pull?

 

[stonyloam]

Re: Merc 470 over heating at WOT HELP

Just a thought; can you reach the flapper parts from the exhaust on the inside of the engine compartment? If not is the drive hard to pull?

No, you have to pull the drive. Pretty easy. Remove the trim cylinders (at the back of the drive) and 6 nuts. Need an alignment tool to put it back on (e-bay). Manual #6 should cover your outdrive. You can download it from "adults only), #9. You can check the gimbal bearing and lube the u-joints while yo are at it. Good luck.

 

[oilydogg]

Re: Merc 470 over heating at WOT HELP

check your riser and exhaust manifold. sounds like a high speed overheat. and idling at 165 degrees is still running pretty hot.

 

[jt2004]

Re: Merc 470 over heating at WOT HELP

Your shutters are suppose to go right after the second exhaust bellow (off the back of the motor there is the bell shaped, a piece of cast pipe, and then the next rubber sleeve in to top of that pipe leading to the outdrive) so your going to have to get in there anyways so you might as well get started. 160 Should be the temp we run at if you have an alum exhaust manifold (it has a 160 thermostat) unlike the cast iron manifolds they have a 140 thermo. wot overheat involves the cooling system inside usually not sea water pump and system. Ever run a jug of system flush through it?

 

[jt2004]

Re: Merc 470 over heating at WOT HELP

and yes you need your shutters, you never know when you are going to get a surge up the riser