Mercruiser overheating, please help.

[bawla47]

hi,hoping i could get some help, really a bit frustrated with this engine. it is a 1978 Mercruiser 470

ive had an overheating problem that i cant seem to fix.
reading extensively on here, ive done the following in the last few weeks.

installed
new lower unit water pump kit
160 degree thermostat
water temp gauge
upgraded 4" heat exchanger
electronic ignition(ditched the points)
timing was pretty advanced, so i turned it down to about 8-10 advanced now.



engine gets to over 210 idling at about 1500 rpms.
this cant be normal? i ruled out that my exhaust riser is clogged as i see plenty of water coming out of my propeller etc, but is this all that is left to check? where exactly do you pull this part from and will i need any new gaskets when putting it back?


thanks alot in advance for your response!
Jaymie

 

[Don S]

Re: Mercruiser overheating, please help.

Have you actually verified with one of those inexpensive IR temp guns that the engine is actually overheating????? At 210?, you wouldn't be able to keep your hands on the engine near the temp sender for more than a second without being burned. At 180, you could keep your hand there for about 5 seconds.

 

[bawla47]

Re: Mercruiser overheating, please help.

wow thanks for such a quick response Don.

i believe the sender is accurate. when shutting the motor off at that temp, my coolant overflow fills up real steamy and the coolant boils for a bit.

im a bit stumped. im not sure actually if what im getting out of my propeller is the full flow of what i need, but i can probably take alittle video and post it. it does seem like alot though. ive put the hose on full flow before, and it flows completely through the system and out the propeller. anything else i could check out maybe?

 

[jfl1959]

Re: Mercruiser overheating, please help.

Hello
The risers are right on top of the exhaust manifold, usually four bolts into the manifold. There are gaskets that will need to be replaced, they usually go on dry(no sealant)

If the system is FULL FWC as opposed to 1/2 FWC then the exhaust manifold is cooled by antifreeze as well and the antifreeze is blocked from the riser by a silver plate that prevents the flow from the manifold into the riser.

If the system is 1/2 FWC then the seawater goes through the manifold as well as the riser and goes overboard.

How can you tell you are getting plenty of water out the prop? If you are testing it on muffs then it is very possible that the flow of water is restricted and under force not enough water is flowing.

Any way good luck, keep us up to date.

 

[Don S]

Re: Mercruiser overheating, please help.

Before you do anything, When the engine cools down, raise the drive up and raise the bow of the boat up so the engine is sitting front of the engine higher than the back of the engine. Take the cap off the reservoir and fill it up.
My guess is that the front of the motor is low so you can have the drive down to run it and you probably filled the cooling system the same way. You then end up with a big air bubble in the back of the block. Till you fill it with antifreeze, it will overheat. You have to have solid coolant, no air bubbles.

 

[bawla47]

Re: Mercruiser overheating, please help.

tilted the bow up as much as i can, and filled it a bit more. same deal

when i first replaced the coolant, i didnt open every drain plug, i just pulled off the heat exchanger. i noticed a pasty goo come out of 1 of the hoses, i guess that happens after too long with antifreeze?


is it possible that the motor is blocked up somewhere else? i figured the cooling system was under high velocity, so itd be hard for somewhere in the block for this stuff to get stuck.

thanks!
Jaymie

 

[jfl1959]

Re: Mercruiser overheating, please help.

pasty goo is not good. water must circulate and not be restricted. What is the goo where did it come from. Is it in the tubes of the exchanger or anywhere else? Would it restrict water flow? Fix that before you waste time looking further