Overheating above 3500 rpm 351w Omc 800

[Bryan_S]

hey folks got the engine in and outdrive lubed, took the boat out to lake washington... and it overheated at 2000..... figured out I installed the thermostat backwards.... ooops =]

so after installing my 160 degree thermostat, I took the boat out again to puget sound and it ran fantastic... other than overheating when i wanna go fast. above 3500 rpm brings the temp guage up fast.

Ive noticed a small .... very small restriction in the upper "radiator" hose..... like the bend in the hose is slighlty oval instead of being round. It's the only thing i can think of that would cause it to overheat only at high rpm.

I plan on taking care of this today as i have plans to be boating all weekend =]

if anyone might have an area of interest for me to check out, please post it.

Im a boat newb, although ive had boats in the past, this is the first I/O.

thanks for reading, and replies

~Bryan S

 

[jerryjerry05]

Re: Overheating above 3500 rpm 351w Omc 800

Sounds like it could be clogged risers.Or maybe the manifolds AND the risers.
How old are they??? Is the impeller new?? J

 

[Bryan_S]

Re: Overheating above 3500 rpm 351w Omc 800

the manifolds and risers are brand new.. so that rules them out. Also the exhaust stays nice and cool. This is a closed cooling system.

~Bryan S

 

[Bryan_S]

Re: Overheating above 3500 rpm 351w Omc 800

no other opinions? ahh shucks!

 

[Howard Sterndrive]

Re: Overheating above 3500 rpm 351w Omc 800

plugged heat exchanger and or p/s cooler if you have p/s

 

[bruceb58]

Re: Overheating above 3500 rpm 351w Omc 800

If your manifolds and risers stay cool, that is usually a good indication that your raw water flow is good and you impeller is working properly. You must have an aftermarket cooling system. Many of those can be marginal if the water is warm but since you are running in pretty cool water, I would look for clogging in the heat exchanger like Howard mentioned.

What closed water system do you have? Since your manifolds stay cool am I assuming correctly that you only have a half system(means no coolant in the manifolds)?

 

[Bryan_S]

Re: Overheating above 3500 rpm 351w Omc 800

yes its a san juan heat exchanger.

When i replaced the engine, i hosed it out pretty good, seemed to flow from every hole i put the hose in.

What should i look for as far as clogs?

no coolant through the manifolds

 

[bruceb58]

Re: Overheating above 3500 rpm 351w Omc 800

You may actually want to give them a call about your situation. I have called them before when i was thinking about installing a system. They were very helpful with me.

 

[Bryan_S]

Re: Overheating above 3500 rpm 351w Omc 800

umm heh

I think I may have finally figured this out...... why i didnt look a while ago... i dunno.

turns out my "fan belt" was so loose i could turn the water pump by hand

the alternator mount hole broke... so i had to jerry rig it to fix it.

gonna take it to a rebuilder, and have a new case put on it.

i sure hope this works!

thank you

~Bryan S

 

[WizeOne]

Re: Overheating above 3500 rpm 351w Omc 800

If the belt was that loose, you'd think it would have been sqealing like a stuck pig, but if the pump pulley was not turning, that would certainly do it.

 

[Bryan_S]

Re: Overheating above 3500 rpm 351w Omc 800

it did make alot of noise when i would say "stab" the throttle.

but my new engine is rated at 300hp, and Ive read these OMC drives can handle a max of 300hp, so i never just gun it, I usually ease into the throttle.

so i took the boat out this weekend. Launched at magnusson park in lake washington, then went through lake union, and out through the locks into puget sound.

the lake temp is 68-70 F the boat temps were fine for the most part, unless i went over 3300 rpms. I never stabbed the throttle, id always ease into it, so i did not notice the belt noise. While on the sound (52F) i decided to hit it a lil harder since the water was 16-18 degrees cooler, i figured it would take a little bit longer to heat up. When i gunned it i did hear alot of belt noise, and took the throttle down immediately, and eased it upto speed. This is when the lightbulb in my airy lil head went off

So not wanting to stress anyone out on the boat (boat full of first timers) i decided to just cruise at low rpms, and let them enjoy the sights of the city.'

When i got home yesterday, I took a peek at the belt tension......... and.... OH MY GOD.

I cannot believe that after all of that, it was the belt tension. I figured it was good this whole time and just was not thinking it was something so simple...... ya know what i mean, ya install it....... its a belt.... how hard is it?

so hard it stumped me for 3 trips!

feelin kinda stupid :redface:

thanks again,

Bryan S

 

[FLboat]

Re: Overheating above 3500 rpm 351w Omc 800

HI Bryan I was reading your post as I have the same problem just my engine is a volvo 4.3 , I did check the belts and found the alternator belt isn't tight enough . the other belt for the water pump is more or less ok . By your experience with the belts Do you think it matters... Thank you

it did make alot of noise when i would say "stab" the throttle.

but my new engine is rated at 300hp, and Ive read these OMC drives can handle a max of 300hp, so i never just gun it, I usually ease into the throttle.

so i took the boat out this weekend. Launched at magnusson park in lake washington, then went through lake union, and out through the locks into puget sound.

the lake temp is 68-70 F the boat temps were fine for the most part, unless i went over 3300 rpms. I never stabbed the throttle, id always ease into it, so i did not notice the belt noise. While on the sound (52F) i decided to hit it a lil harder since the water was 16-18 degrees cooler, i figured it would take a little bit longer to heat up. When i gunned it i did hear alot of belt noise, and took the throttle down immediately, and eased it upto speed. This is when the lightbulb in my airy lil head went off

So not wanting to stress anyone out on the boat (boat full of first timers) i decided to just cruise at low rpms, and let them enjoy the sights of the city.'

When i got home yesterday, I took a peek at the belt tension......... and.... OH MY GOD.

I cannot believe that after all of that, it was the belt tension. I figured it was good this whole time and just was not thinking it was something so simple...... ya know what i mean, ya install it....... its a belt.... how hard is it?

so hard it stumped me for 3 trips!

feelin kinda stupid :redface:

thanks again,

Bryan S