Still running hot

[Quadruplecccc]

I have a 1976 merc. 233hp (351 windsor).Standard cooling. Was remanufactured 2yrs ago for previous owner. Said owner put larger cam in motor. Constantly ran hot and got to work on it but quickly got stumped as to why it ran so hot. Timing was off by quite a bit. Adj. made and runs great. Thought this would fix it but didn't. Pulled the heads and had them rebuilt by reputable engine builder. (He did find some problems that he fixed) New water pump in outdrive, circulating pump good, lots of flow coming through manifolds, elbows luke warm at full temp. 190* to 200* Here's the big question: Is it possible that the cam and the tight motor generate enough heat to make it run this hot? My last stock motor ran at 140* to 150*. Does beefing up a motor raise internal temps this much. I'm reluctant to run this thing on the lake under load although it seems to top out at 200* on the garden hose @ 2500rpms. All the cooling lines are where they need to be. Thought temp. sensor might be bad so I changed that , Had same results. I'm stumped ?????

 

[havasuboatman]

Re: Still running hot

When it's running, can you put your hand in the water as it exits the boat? You said the risers were luke warm. Can you lay your hand on them?
If you said yes to either question, the motor is NOT running at 200 degrees.
Your guage may be faulty.

 

[Quadruplecccc]

Re: Still running hot

I pulled the hose off the front of the manifold while it was running. Water shot up about six inches and flowed over my hands. It was hot but tolerable. I can keep my hand on elbow for as long as I want. The manifold starts to get a bit uncomfortable after about 15 sec though.

 

[havasuboatman]

Re: Still running hot

I pulled the hose off the front of the manifold while it was running. Water shot up about six inches and flowed over my hands. It was hot but tolerable. I can keep my hand on elbow for as long as I want. The manifold starts to get a bit uncomfortable after about 15 sec though.

Your boat isn't running at 200 degrees then. Replace the gauge and sender with some that are matched. All gauges don't use the same ohm's range, the gauge and sender have to be matched.
The P/O may have used the incorrect sender when he rebuilt the motor, or the gauge may just be toast.
The fact that you can touch the exhaust manifold at all says your boat temp is just fine. With the block temp at 200 degrees the exhaust manifold would be so hot it burned the skin of your hand.

 

[madurodave]

Re: Still running hot

my gauge is off by about 25 degrees. Thought was running around 180 but tested with thermo gun and found out the gaueg was wrong.

 

[Quadruplecccc]

Re: Still running hot

I had hooked my old guage up to it last year and it read the same as the one in the boat.To day I put my old sending unit in the intake and hooked up the boat gauge to it and had same results . I may have to hook up the old guage to the old sending unit to make a matching pair. After that I may have to borrow a heat gun.

 

[Quadruplecccc]

Re: Still running hot

Got out today and wired my old temp guage back at motor. Ran at 145* when other said 190* .Pulled other guage out of dash and found a short in the wire. Fixed short and now both work. Thanx for all of the input on that . Unfortunately , as I was checking the linkage and making sure it would go into gear propperly I heard and felt a slight knock or thump asthe outdrive was spinning. Went away when in neutral. Prop spins ok , what else might cause this to happen?? Thanx!