...Risers running hot -- followup.

rpengr · **Posted:** Wed Nov 05, 2014 11:42 am

So I'm getting ready for our annual trip across southern Florida this weekend, and have completed my annual maintenance (except for the outdrive, which will wait a little longer):
Oil Change
Oil Filter
Fuel Filter
New Impeller
New Belts
3 new hoses
Remove, clean, paint manifolds and risers (Osco brand, new last year)
Replace with Volvo Metal Gaskets, as the Osco gaskets had slight leakage.
Remove, paint and re-gasket the thermostat housing

Everything is running perfect, but the risers are running hotter than they should. After extended idle, they can be 135/160deg (degF). After cruising 20 min at 3500-4000 rpm, they were 175/205 deg. Not extreme, but too hot to keep you hand on. The top and sides of the manifolds are only 100/120deg, only the risers are that hot.

This weekend cruise will be 170 miles round trip with 7 adults and baggage, so I want to make sure it is cooling OK.

Hoses did not feel particularly pressurized. Since impeller is brand new (and the old one did not have any broken pieces), I am hoping it is just a restriction in the thermostat housing. This afternoon, I will take it off and drill out the openings, that do have some rust buildup in them.

--Does anyone know what size the ports are? I'm thinking at least 3/8" diameter for the two outlets, and 1/2" diameter for the raw water pump inlet...or are they bigger than that.

--Comments on the above temperatures?

--Do the Osco risers run hotter than the Volvo's?

--How much flow should I see if I pull a hose off (thermo housing to exhaust manifold) while engine is running? Like a full garden hose stream out each side?

I will be back to the boat this afternoon to further diagnose. I think the thermostat housing will fix it, but I appreciate your comments.

Ray

ps: Engine temp is perfect (temp gage is not numbered, but indicates 40% of scale once warmed up at idle or cruising)

LouC · **Posted:** Wed Nov 05, 2014 11:59 am

The only manifolds/risers that I've had on my old boat are the OMC one piece units and they run a good bit cooler if everything is right with the cooling system (idle 90-100, after coming off plane 135). How are the water exits on the end of the risers? You don't have flappers, right? Asked only because if the fall down they can block the exhaust. It is possible for rust to neck down the passages in the Thermo housing over time. How is your raw water output with the boat in the water? I had sucked up sand in a shallow area last summer. First sign was engine temp getting a little higher 160-->175 and when I checked the upper end of the manis (riser section) they were 160. Pulled boat replaced impeller and wear plate/cage and back to normal.

john55c · **Posted:** Thu Nov 06, 2014 7:40 am

LouC wrote:

Pulled boat replaced impeller and wear plate/cage and back to normal.

Which is a 10 minute job on the OMC Cobras...one of the great design features of that drive.

Love how simple it is to work on.

Keep us posted Ray on what you find when you open everything up.

rpengr · **Posted:** Thu Nov 06, 2014 8:24 am

Thanks Lou and John. Yes, I miss my OMC "Bat Wing" 1 piece manifolds on my old 4.3 ...and miss the OMC impeller location!

Here is the Update:
Last night I pulled the thermostat housing and tested it with garden hose. Flow was somewhat restricted out the exit holes. The exit holes were rusted down to about .28" or .30" diameter.

I drilled open the two exit holes to .421 diameter, which seamed larger than stock because I was removing some virgin cast iron, not just rust. Also cleared the inlet hole with a drill. Now the garden hose flowed better, but more water would come out one side (port) than the other unless I blocked it with my finger. Perhaps I should have stayed at about .375" diameter so they would flow more evenly.

Re-installed on the engine and test ran. Could not go above 900rpm to avoid complaints from the neighborhood, as it was 11:00pm. The port side riser, that was running 135deg before, is now down to 110deg. The Starboard side riser, that was running 160deg before, is now down to 135deg.

Big improvement, but not perfect. By drilling the holes to .421 diameter, I might have made it too easy for the water to go to port side. Hopefully the starboard side will get more water at higher RPM. I will bring a little clamp to restrict the port side hose to balance it out if needed.

I am "GO" for this weekends trip, and will see what temp they reach under heavy load. (Next step would be a new thermostat housing, which is currently the original).

Ray

ric · **Posted:** Thu Nov 06, 2014 9:24 am

Give it a month, it will rust back to it's correct size

LouC · **Posted:** Thu Nov 06, 2014 4:38 pm

I replaced the original one back in 2002, the one I put on then is still pretty good, I have rodded out the holes for the manifold water feeds with a coat hanger a few times. They do corrode inside, this is why when I winterize the engine n manifolds I fill em with -100 marine af for the long winter nap. It keeps out air (FE/O2=rust) which definitely reduces corrosion. In fact the original t stat housing was quite a bit more rusted than this one is, after close to the same # of years of use, because I've been filled the engine with AF every winter.

rpengr · **Posted:** Mon Nov 10, 2014 9:27 am

Followup:

Went on the 160 mile cruise this weekend, and the boat performed perfect. (It rained all day Sunday, but that's a different story). While cruising at 3600 rpm with 7 adults plus baggage, the risers measured about 130-145 degrees. Very happy with that.

Ray

.

Selfie.
Saturday was sunny and 75 deg. This pic was on Sunday...60deg and rained all day. Still better than being at work

LouC · **Posted:** Mon Nov 10, 2014 5:05 pm

Perfect, that's a good temp. Thanks for the follow up, that's how we all learn...

john55c · **Posted:** Tue Nov 11, 2014 8:30 am

That's awesome! Where is your trek to/from? How much gas did you end up using?

rpengr · **Posted:** Wed Nov 12, 2014 6:04 pm

john55c wrote:

That's awesome! Where is your trek to/from? How much gas did you end up using?

We launch in Belle Glade Florida (1 hour trailer west from West Palm Beach, FL). Then we cruise the Lake Okeechobee Rim Canal to Moore Haven, FL, then the Caloosahatchee River to Fort Myers Florida. 170 miles round trip took about 65 or 70 gals this time loaded up with 7 adults and quite a bit of stuff. Best Western Waterfront hotel in Ft Myers is only $82/night and free docking.

rpengr · **Posted:** Wed Nov 12, 2014 6:06 pm

LouC wrote:

Perfect, that's a good temp. Thanks for the follow up, that's how we all learn...

You can see in the background what a Floridian looks like when it gets down to 60deg. :lol:

LouC · **Posted:** Wed Nov 12, 2014 7:00 pm

LOL, we have had above normal temps for a while and I took advantage of it to do some boat jobs and tune up our old '98 Jeep Grand Cherokee which is now my son's vehicle. Its going to get cold and my old fingers don't do so great then. Last April I had to replace a starter in the same Jeep on a day when it was 24 degrees out. Yes got it done the things you do for your child. Its going down to 28 degrees Thurs nite and we might get some snow flurries Fri morning.

I love Long Island but gotta get a place warmer for the winter. If this place did not have winter it would be the perfect boating environment.

john55c · **Posted:** Thu Nov 13, 2014 6:54 pm

rpengr wrote:

john55c wrote:

That's awesome! Where is your trek to/from? How much gas did you end up using?

We launch in Belle Glade Florida (1 hour trailer west from West Palm Beach, FL). Then we cruise the Lake Okeechobee Rim Canal to Moore Haven, FL, then the Caloosahatchee River to Fort Myers Florida. 170 miles round trip took about 65 or 70 gals this time loaded up with 7 adults and quite a bit of stuff. Best Western Waterfront hotel in Ft Myers is only $82/night and free docking.

That'a pretty awesome! I would love to do a trip like that. At some point, I plan on circumnavigating Cape Cod by boat. Need the perfect tides, calm winds, and preparation. Sounds like a fun trip and waterfront with dock for that price? That's unheard of up here. The municipal docks charge $3-6/foot/night, let alone hotel!

www.iFourWinns.com

...Risers running hot -- followup.

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