3.0 thermostat issues

[tech62571]

hey,
im trying to replace the thermostat cause it started to run at 175F but i am seeing different things as to temp.

im reading some say 140F for salt water and 160F for fresh water.
official parts say 160F (part# 807252T2)

looking for some advise on which to use

also is there a trick to remove the plastic housing?

and does this black stuff look normal? it feels like dirt not grease (see pic)

[mmwjr]

Raw water cooled in salt water 140 F to stay below the crystallization point of salt. Not sure what the black stuff is.

[tech62571]

thx for the reply..
i figured out its small pieces of rust
there is some in the hose too
is that normal?

[donald]

I am thinking you have a large amount of rust scale in that engine and more than likely blocking exh elbows.
Don

[tech62571]

is that normal?
can i flush that out?

[mmwjr]

Yup rust scale. No easy way to clean it out. I had to replace the engine on my first boat due to this as it was causing overheating all the time. I did try removing the heads and scraping the water jackets and got one additional year out of it.

[tech62571]

ok thanks for the info.. appreciate it

[tech62571]

i cleaned and flushed everything but it still overheating.
looks like almost all the water is coming out of the prop.

any ideas why? or where to start looking?

[mmwjr]

The two ports on either side of the transom assembly are for idle and at higher rpms most of the water will come out the prop, what rpm are you at? Have you performed the flow test to verify the engine is getting the correct flow of water? See the Mercruiser manual.

[tech62571]

it was at idle
i dont know how to do a flow test

[mmwjr]

Idle being 650 rpm?

See the mercruiser manual for you engine under Documents

[tech62571]

yes about 650

[tech62571]

so i pulled the elbow and it doesnt look too bad.
i ran water through the manifold and its flowing good. doesnt look obstructed at all.
the elbow could be obstructed but i cant flow test it other then running the hose into it.

i ran water through the block and it flows good out of the head.

does this have a circulating pump? i cant think of anything else.

i put a new thermostat in but hard to tell if its working

[mmwjr]

I would consider that end of life. It’s near the point when failure will occur allowing water to get into the exhaust.

[donald]

I agree with Mike.
Time for new elbows and manifolds.
Don

[tech62571]

thanks guys

[tech62571]

i replaced the elbow and im still getting the same issue.
over heating but most (almost all) of the return exhaust water is coming out of the prop.

any ideas why?

i cant figure out how the water goes to the idle ports and prop or why it changes when underway

[tech62571]

after more troubleshooting.. i found out there is no water coming from the impeller.
is it possible the shaft that spins it has an issue?
is there a way to test that?

[tech62571]

can i run the engine briefly with the lower unit off the outdrive? to see if its spinning?

[mmwjr]

If you put the shifter into gear and the propeller spins the shaft that turns the impeller is turning. Missing key, bad collar in the impeller or just worn impeller.