Merc. 233hp running hot

[Quadruplecccc]

Hey everyone! I've been working with this motor for some time now workin out all the bugs.

Had timing and carb issues wich I've taken care of. Now have great acceleration, runs smooth. starts great and peaks out at about 4k rpms. (book says should be between 3800 and 4000rpms)

I discovered this problem last year and can't seem to get it staightened out.

Motor runs up to 180* under load and stops there. When not undr load motor cools to about 160* and stays there. Is this normal???

This is a 76 merc. 233hp that has been rebuilt and slightly cammed up.
Here is what has been done so far: changed water pump in out drive(last year), circulater pump (this year), checked and inspected manifolds/risers ,new t-stat, changed temp. sensor, checked for blockage in cooling passages in motor (clear), had heads redone by a pro, new head gaskets ( in correctly). Also changed temp guage.

While on muffs , lots of water evacuating motor at transom. Climbed inside and pulled hoses off one at a time to check flow. Great flow coming from each hose.

I'm starting to believe this motor just wants to run at this temp but from what everyone says here this should not be, so now I don't know if I'm chasing after a problem that doesn't exists.

What did I miss? I'm stuck! Had boat out this weekend and ran her 32mi total duing the day watching temp very closely. Never went over 180* Am I nutz??

 

[jerryjerry05]

Re: Merc. 233hp running hot

If the manifolds are original the risers are probably corroded.They can look good but need to be replaced.If it cools at slow speed but goes up at speed that's a classic sign of bad manifold/risers.Not enough flow.
They sell a heat gun at Home Depot.About $30 It will really tell the temp if needed.
Another thing,timing being off could do that.The max RPM should be about 4400RPM.If your prop is a 19 pitch then dropping to a 17p will raise the rpm and improve performance.Having the motor labor could do that too.
But I'd guess the manifolds/risers.J

 

[Bt Doctur]

Re: Merc. 233hp running hot

Thermostat housing could be clogging up some.

 

[haulnazz15]

Re: Merc. 233hp running hot

You should be between 3800-4200 rpm for that engine. I assume you still have the original log-style manifolds/risers? I pulled mine off (same engine/drive/year) this winter and literally dumped piles of soot and rust from the manifolds/risers. I would inspect the thermostat/housing as they are likely covered in rust if they haven't been pulled.

The good: the way they ran the cooling on the 233, there's no passage of water between the risers/manifolds so you don't have to worry much about that gasket failing. However, I did have an exhaust passage in the head that had corroded through which allowed water into a cylinder or two.

Your engine needs a tune up, so get a timing light and verify that base timing is set at 10BTDC, as incorrect timing could be an issue in addition to the prop size. I believe the stock thermostat was 160-degrees, but the thermostat that came with my new center-riser manifolds is a 140-degree.

 

[Quadruplecccc]

Re: Merc. 233hp running hot

Clymer book says I should be between 3800 and 4200 rpms at wot. I would think that 4600 rpms would be a bit much.

I have timing set at 10* btdc and runs great there.

Exhaust shutters changed last year and pulled motor this year to check on their condition. They are good.

Thermo. housing was off and cleaned during reassembly of motor. No major scale there.

Book calls for a 140* thermostat. (thats whats in)

Replaced manifolds and elbows about 7 yrs ago and they look great inside. Really I haven't used the boat in salt enough to even cause any sever rust. I hooked a hose up to them before reinstalling them to check flow coming out and all that did was get me soaked ha ha.

I'm currently running a 17 pitch prop , giving me 4000rpms. Comes upon plane quickly and overall performance seems to be where it should be

What are we missing?

 

[haulnazz15]

Re: Merc. 233hp running hot

Well my only suggestion would be to grab the IR temp gun and check for sure. If the temp never goes above 180, and you have good oil pressure, then go have fun. Nothing seems to be out of sorts really, and the performance cam you have may cause it to run a bit on the hot side.

 

[Quadruplecccc]

Re: Merc. 233hp running hot

Thanks for all your help, I'll go get a heat gun to confirm temp.