overheating at high speed/rpms

[vinnimon]

I have a 140(3ltr) mercruiser, I have done a total rebuild on this engine. you name it, it has been done. Between 15 to 38 mph my temp gaugegoesto the max almost immediately, at 3mph it is running cool. Is there any chance that,frequenting diferent bodies of water that my waterpump in the stern drive my be plugged, or failing at higher speeds.I want to replace it myself, but im not what I might be getting into.

 

[Bifflefan]

Re: overheating at high speed/rpms

sonds like the impeller.
Never hurts to change it.

 

[TowRoper]

Re: overheating at high speed/rpms

i would start by looking for blockages in the cooling system and if its clean change the impeller

 

[vinnimon]

Re: overheating at high speed/rpms

I was told about the impeller, I was under the assumption that it had been replaced.I know for a fact that everything above(engine wise) is perfect. I am a truck mechanic by trade, I have done a lot of overhauls, I have also tinkered with lower units in old outboards(i.e replacing a waterpump in a 35 chrysler outboard). Now to replace this impeller,or to clear up any blockage, is this something I should attempt on my own, or am I best to send it in.thanks V

 

[TowRoper]

Re: overheating at high speed/rpms

trust me being an old trucker my self you can handle this. same stuff just looks different lol

 

[vinnimon]

Re: overheating at high speed/rpms

do you know anything to be aware of when replacing the the impeller,cant find my manual. Or anything to watch out for.

 

[TowRoper]

Re: overheating at high speed/rpms

cant think of anything special to look out for other then making sure your seals are in properly

 

[vinnimon]

Re: overheating at high speed/rpms

That is obviously a given, I thank you for your input it was a great help. hope to chat again. P.s. If your a fisherman like me I found a little trick for pickerel/walleye that you may want to try. A powerbait lemon/lime sented 2in jig thin tail, put a slit on the top, and imbedit with the native forage fish of the lake your fishing. Its worked wonders for me. V hamilton, ontario.

 

[TowRoper]

Re: overheating at high speed/rpms

love the walleye! i will give it a shot! good luck with your boat too there will be other replies to your thread here with allot more great input

 

[vinnimon]

Re: overheating at high speed/rpms

The l/l jig was luck, the rest was from watching the locals. I will keep an eye out on any replies to me. bye the way, thank you very much for help/input. I feel a lunker hitting your line right now. thanks V

 

[Bt Doctur]

Re: overheating at high speed/rpms

http://www.boatfix.com/merc/Servmanl/6/6covr3.pdf
Do the full kit to rule out a warped pump base that couold be sucking hot exaust gas.

 

[vinnimon]

Re: overheating at high speed/rpms

the full pump kit? that is strickly in the stern(lower unit).