engine overheating

[coolchange]

Big block Mercruiser w/FWC

Just started for the first time after: winterizing, replacing exhaust flappers on both sides, flapper change caused replacement of the gaskets on the riser. ( I was careful to get the blocking gasket back where it came from I think) Impeller was changed last year and has 75 hrs.

New anti-freeze (50/50) put in 2 gallons for the engine and a cabin heater

manifolds hot, riser elbows barely warm, water coming out of the exhaust and further up on the drive (toward transom). Hoses to the risers slightly warm. I planned to top off the anti-freeze...is it poss that there was just not enough? (always looking for the simple solution ...and it doesnt always turn out that way)

Since the boat ran fine going into winter, there is no anti-freeze in the bilge, temp has always been steady at 175 but today hit 250

Engine did not smelll burnt,or even hot

So: what diagnosis can you guys offer? What information is needed to track this down? I plan to start with topping off the antifreeze (is it poss that 2 gal just didnt get it full enough??

[SomeSailor]

Bob changed his manifolds last year and had a heck of a time getting all the air out of the system. Where is the blank-off plate located on your risers? (above or below the blocks?)

He cured the air problem by installing a simple lever-type radiator cap of the same pressure rating. This allows to "burb" the bubbles out of the system as it's purging.

You might also has gotten some plumbing crossed? Get two hoses swapped and you lose proper coolant flow. Does it overheat on the muffs as well?

[3788sam]

Had a similar problem with air in the system on a crate engine install. it took us 3 times bleeding the system until we got the air out. Pressure raises the boiling point. Any air in the system won't allow the pressure to build and it will get hot fast!

[coolchange]

I think (and hope) you two are on the right track...I did find out at the dealership that this setup should take about 4 gallons of coolant and as mentioned I had only slightly over 2...a significant air bubble eh? I picked up a new thermostate for just incase this one is frozen..

SS: I forget which was the blocking gasket but was pretty carefull about what went where....as to switched hoses probably not likely as these are all formed and would be really hard to mess-up (I only removed one end of the hoses..)

More tomorrow.

[beyond kelp]

I think you guys have helped me figure out why my temp is a bit high also. Ill try the automotive cap and see if it helps- This forum is cool 8) ! Thanks Mike for your efforts on IBNW!

[coolchange]

OK I will have a trip down the Columbia this week....it seems that the big ol merc with a water heater and cabin heater hooked to FWC takes a little over 5 gal of coolant and 2 beano tablets. I believe all air is out, temp on the muffs is 165 (idle) seems that being 60% short on coolant aint right.

I have to finish loading, put the two side windows back on and probably a few minor details (ha!) :D